Experimental IMR Enduron Powder Loads – Discussion & Results

Editors Note : Caution, Reloading is dangerous, read our “Reloading Disclaimer“. The IMR Enduron Powder load data published by this website is intended discussion purposes only. As with all data collection, mistakes are possible. You have been warned.**

New IMR Powders
New IMR Enduron Powders
Bob Shell
Bob Shell

U.S.A.-(Ammoland.com)- It seems every day new items including guns, ammo, bullets, new calibers, scopes and various other shooter related items are released.

Another new item is gun powders that have characteristics not present in the older propellants. Over the last few years, there have been some novel improvements. Bright spots include gun powders that have chemicals in them that are used to reduce copper fouling.

In addition, the new powders are not heat sensitive a problem that has been around for years.

Hodgdon – The Gun Powder People ( www.hodgdon.com ) has the rights to the IMR line of gun powders so I have been dealing with Chris Hodgdon in regards to these powders in various rifles. The Hodgdon folks have done a lot of development with the modern and common rifles so with Chris' feedback, I have done some work on them as well

I am focusing on new IMR powder loads for rifles that are obsolete but can deal with a modern type of smokeless powder loads.

Military surplus rifles are common and I have worked a lot on them, from the early smokeless powder loads through the WWll rifles. There are many of these guns still around and with the reasonable prices that they have, popularity is still good. These guns are well made, durable and unless they have been shot excessively or are abused, they are still well worth shooting. For those who like to hunt, they are powerful and accurate enough to get the job done. For the most part, brass and bullets are plentiful or at the worst can be made by the experienced handloader.

In this test, there were a few obsolete sporting rounds. With these powders, I am looking for good performance, which includes good accuracy and velocity with safety in mind. Trying to exceed the original ballistics is not my goal but some improvements did happen on some occasions. If this was achieved without excess pressure then that would be acceptable.

When working up loads with any powder, caution should always be exercised. Start on the low side and carefully work your way up until you get the safe load that you are seeking.

Since every rifle is an individual these loads should be used as guides. As you develop your own loads you will get different results with your rifles. All of these loads listed were tried out by me and not copied from another source.

I did not do much with modern magnum rifles because that data is available and with limited time and resources, I didn’t see the point. I did try a couple of loads in the 7 mm and 300 Win mags and the results are promising. If I ever go on another hunting trip and use a suitable rifle for one of these powders I will work up the loads and use them. At some point, I will work with the 8 mm Remington mag as the 7977 should really do well especially with a heavy bullet.

Recently IMR introduced four new powders. Pictured is the 7977 IMR Enduron Powder.
Recently IMR introduced four new powders. Pictured is the 7977 IMR Enduron Powder.

Recently IMR introduced four new powders. They have a feature known as Eduron technology. A couple of features of this technology is a reduction in copper fouling and it is insensitive to temperature changes.

It seems that every day a new powder is coming out. Most reloaders have favorite powder for their guns but with the supply problems having backup loading info on powder alternatives is always a good idea. Since data has been worked up for the common guns, I don’t see any point in duplicating someone else’s work.

Many of the WW l and WW ll guns are still around and the owners want to shoot them. Brass and bullets are still available, so as long as the gun is safe why not shoot it.

IMR Gun Powders used in this study Include:

Having worked with the new IMR Enduron powder I have observed some of the following characteristics. They are an extruded item resembling many of the other IMR powders. They don’t appear to be heat-sensitive per a couple of tests I did. In my powder measure tool, they are NOT very consistent. I may get several good throws then one will increase anywhere from ½ to a grain. With that observation, I measured each charge on the ones for serious work. Maybe it will meter better in another powder measure tool so the best advice it to try and observe it in yours.

I have listed virtually all of the loads including the ones that were too warm. The purpose is to inform the reader and to use caution when approaching the max loads, as they are listed as a study only. These are new powders and as with all handloading, each gun is an individual and what is ok in my weapon may be too warm in yours or the reverse can be true. In quite a few instances, the new powder gave some more velocity. More importantly, they gave good accuracy and consistency, meaning a low standard deviation from shot to shot. In some cases, you can take your rifle and improve on these loads if you take the time to research and observe your own results.

As for the brass used it was whatever I had available with no effort to sort it by brand or weight.

Contrary to some opinions brass with mixed headstamps can produce very consistent and accurate ammo. As long as the brass is in good shape, it will work.

You will note that some bullets were loaded backward. One reason is the flat point bullet wasn’t available therefore a boat tail bullet backward was used. That makes it safe in a tubular magazine rifle. Most of the time they were as accurate as the same bullet loaded in a normal manner. In addition, you might get more penetration as the back of the bullet is stronger and the info gathered makes it interesting to test a bullet this way. I have done this with various rifles and is seldom disappointed with the accuracy. As with all testing pay attention to pressure signs.

The IMR 4166 Powder may be on the slow side but will be interesting with heavier bullets. In modern type guns, 4166 IMR Enduron Powder is a viable powder.
The IMR 4166 Powder may be on the slow side but will be interesting with heavier bullets. In modern type guns, 4166 IMR Enduron Powder is a viable powder.

The 223 is the most common round being made, so we start with the assumption that IMR 4166 Powder should work well.

First tests indicate that 4166 doesn’t work well in the 223 as it is slow and produces a high es and the loads were compressed. Further testing produced better results.

The 100 grain was fired in a rifle with a 1 in 7” twist and a 16” barrel. We tested to see if they will stabilize in that twist. The 100-grain bullet stabilized at 100 yards showing some good accuracy potential. Looking at the tables it will become noticeable that with some loads adding 1 grain of powder causes a major increase in velocity. That is something to keep in mind when working up loads.

223 IMR Enduron Powder Loads

27 grains 416650 gr. Privi3237.83Good Load
27 grains 416653 gr. HP3193Good Load
26 grains 416650 gr. Privi2926High ES Slow
25 grains 416655 gr. FMJ2721-16" High ES Slow
26 grains 416655 gr. FMJ3221.59---20"Good Load
21.5 grains 416690 gr. Sierra BT HP2364WARM!
21 grains 4166100 gr. HP2269 16"Nice

The 22-250 Bullet is a top performer in the 22 centerfire class. It is my favorite 22. This cartridge has been around for many years as a wildcat before Remington adopted it in 1965. It is a very flexible round and I have put many pasture poodles to rest with it over the years. For that purpose, a 50 or 55 grain seems to be the best option.

22-250 IMR Enduron Powder Loads

36 grains 416650 gr. Privi3934.1High ES
35.5 grains 416653 gr. HP3700.87Fair
35 grains 416655 gr. FMJ3658.7Very High ES
35 grains 445177 gr. HP3196.59Decent Load
32.5 grains 4451100 gr. HP2792.2 High ES

The 243 Bullet should respond well to some of the new IMR powders.

The 243 Bullet is versatile and with the proper bullets is adequate for deer and similar size game. I have used it for groundhog hunting and it is slightly superior to a 22 if the wind is blowing. Most of the time I used an 85-grain Sierra, as it was the most accurate bullet in that particular rifle.

As always, keep in mind that different guns like different bullets and powders.

The 243 should respond well to some of the new IMR powders.
The 243 should respond well to some of the new IMR powders.

243 IMR Enduron Powder Loads

39 grains 416665 gr. Hornady3312Consistent
38 grains 4166 75 gr. Speer HP3158Mild
36 grains 416680 gr. Sierra BT SP3174.8Consistent
37 grains 416680 gr. Privi BT SP3212.6Nice Load
41 grains 4451100 gr. Sierra BT 2981.14OK

The 25-35 Bullet has been around for many years. Most are lever action, hence they need a round or flat nose bullet to prevent chain fires. Unfortunately most bullets won’t work & no one makes suitable bullets so I will be loading the bullets backward to produce a flat point.

In the past boat tail bullets have been used by me with success. Since the original bullet is 117 grains, a boat tail bullet should work fine.

**Bullet loaded backward. Boat tail bullets are used for loading backward because with their profile they feed better.

25-35 for testing
25-35 for testing

25-35 IMR Enduron Powder Loads

25 grains 416690gr. Sierra BT *2266Mild Not Consistent
24 grains 4166100 gr. Privi2258.7OK
22 grains 4166 117 gr. Hornady *2118Consistent

The 257 Roberts Bullet has been around for many years and I have a converted Mauser to test a few loads. The rifle is a converted Mexican Mauser which was originally a 7 X 57.

I can get more velocity out of a 257 but I didn’t fully trust that rifle with high performing loads and it also was not my gun. Therefore, I throttled back. Perhaps at a later date, I will be able to pick up another rifle and try again.

257 Roberts IMR Enduron Powder Loads

38 grains 416687 gr. Hornady2786.8Fair-Slow
43 grains 445187 gr. Hornady2623.38Slow
45 grains 4451100 gr. Privi2597.5OK
45 grains 4451100 gr. Privi2645.67Second Test
43 grains 4451117 gr. Horn2534Good Load
45 grains 4955117 gr. Hornady2662.67Nice

The 25-06 Bullet started out life as a wildcat but later on Remington adopted it. For long range on some deer and antelope it would be hard to beat. Later on I will do some more testing with this round.

25-06 IMR Enduron Powder Loads

52 grains 4955117 gr. Sierra3169.2OK=Accurate

The IMR 4451 has a burning rate close to 4350 which will make it versatile. Since many of the common rounds are covered I will go over some of the military such as the 30-40 Krag and similar rounds.

The 6.5 Jap came out to replace the 8 X 53 Murata.

The case is small but due to the strength of the action, loads can be made to compare to some of the other 6.5 caliber rifles. Like most of the 6.5 caliber military guns ammo used a 156-160 gr FMJ RN which gives some good penetration but lacks the stopping power of a larger round.

Lighter, soft point bullets are better for hunting as they possess more velocity and open up upon impact. The action is considered one of the very strongest in existence. It is almost impossible to blow one up as tests have shown that the barrel has been blown off but the action held. That doesn’t mean that you should try and make it a magnum round. There are other limits to consider.

How does it handle gas if there is a rupture? A well designed action such as the Mauser model 98 vents the gas away from the shooter’s face.

Also the case will give up before the action does. Barrel length is a very important factor with velocity. I have chronographed many long guns and handguns and almost without exception a longer barrel produces more velocity. When you take notes of your readings keep that in mind. That is especially true with large cases and max loads.

6.5 Jap IMR Enduron Powder Loads

34 grains 4166139 gr. Privi2468.18Nice
36 grains 4451160 gr. Hornady2284.28Consistent
The 6.5 Daudeteau was the military round used by Uruguay in the 1890’s. It is a conversion of the model 71 Mauser converted to fire this round.

The 6.5 Daudeteau was the military round used by Uruguay in the 1890’s.

It is a conversion of the model 71 Mauser converted to fire this round. France also used the round to a small amount during the same period.

There is no commercial brass or ammo available so it has to be made. The 7.62 X 54 Russian cases seem to be the best option. With a good selection of bullets and some common sense it can be a decent hunting round. While well-made it has only one locking lug so that should be remembered. The Daudeteau loads are right where they should be.

I used the slowest powder as the rifle has only one locking lug so trying to increase velocity a lot would be foolhardy. The long barrel does help increase the velocity.

Son Donald shooting the 6.5 Daudeteau rifle
Son Donald shooting the 6.5 Daudeteau rifle

6.5 Daudeteau IMR Enduron Powder Loads

47 grains 7977140 gr. Hornady2574OK
46 grains 7977160 gr. Hornady RN2400.44Nice

The 6.5 Dutch is the forerunner of the 6.5 X 54 Mannlicher. It is offered in the model 95 but is not available commercially in the United States although possibly could be found in Europe. The rifle is well made with a smooth action and with good loads it is a good hunting round for deer size game. The carbine is light and handy to carry with an 18” barrel. Cases have to be made from 303 British brass which is available. With a good selection of 6.5 bullets, it is a desirable round if you don’t mind a little extra work.

The 120-grain load was excessive and the load would have to be reduced by at least 3 grains or use the 4451 powder as it is slower. The Dutch has a short barrel so obtaining much more velocity would be difficult and unproductive. As a note, the extractor broke during the test but we just poked them out until I fix it.

6.5 Dutch IMR Enduron Powder Loads

37 grains 4166120 gr. Sierra 2631.12Nice Consistent
40 grains 4166120 gr. SierraxxxToo Hot!
40 grains 4451140 gr. Hornady2472.75Consistent
39 grains 4451160 gr. Hornady2308.5 Nice Load

The 6.5 Carcano was one of the earlier smokeless rounds introduced by the military powers. Italy brought it out to replace the 10.4 Vetterli and it served through WW ll.

The Carcano rifle is not highly regarded by collectors and shooters as it is considered inferior to most other period rifles.

However, for those in the know, it is a much better weapon than it is given credit for.

There is a good selection of bullets and, with a little common sense, it will give a very good performance. The Carcano loads can be increased somewhat, although common sense should apply. With this gun, I did start mild and worked up to the top loads listed. It has a short barrel which will put a limit on the velocity. The last 160-grain load is consistent and due to the very short barrel it will be difficult to get more velocity without excess pressure. A 24” barrel would increase velocities by 150 to 200 FPS. If I get a longer barrel Carcano then I may work with these loads some more.

6.5 Carcano IMR Enduron Powder Loads

40 grains 4451120 gr. Sierra2479Consistent
38 grains 4451139 gr. Privi2321.5Mild
36 grains 4451140 gr. Hornady2168.1Very Mild
37 grains 4451140 gr. Hornady2241.2 OK
35 grains 4451160 gr. Hornady RN1972.1 Very Mild
36 grains 4451160 gr. Hornady RN2012.33OK
37 grains 4451160 gr. Hornady RN2148.09Very Consistent

The 6.5 X 55 Mauser round along with the model 96 are highly regarded by shooters and collectors.

Due to the fairly large case capacity, I felt that the 4451 would work well with heavy bullets. The 4955 has a burning rate similar to H-4831 powder so it should work well in this round with heavy bullets. A couple of the velocities are higher than expected. There are no obvious signs of excess pressure but I would strongly recommend starting 2-3 grains below on the loads listed as warm. After some further examination and work, I found that they are a bit too hot for general use. There is no excessive swelling or difficulty in sizing which are signs of pressure. The cases were new Privi so measuring the head after firing might not be totally accurate. A few of the primers seated too easily which is a definite sign of excess pressure. The Mauser model 96 is a great, well-made gun and is the best Mauser action other than the 98.

As noted velocities were higher than normal which should raise a flag.

There are some legitimate reasons for that such as a long barrel or fast gun but any sign should be reviewed. This gun is 100 years old so that should be taken into consideration. Extra velocity may be desirable but not in all cases. The standard deviations (SD) on the warm loads are pretty low, easily within standards for such guns. In general, a high SD means that the load is too light though not always. Safety and caution should come before anything else especially when working with new and unknown powders. This applies to all guns especially the older ones that are tested in this piece.

6.5 x 55 Mauser IMR Enduron Powder Loads

44 grains 4451120 gr. Sierra2878.98OK
41 grains 4451139 gr. Privi2449High ES
43 grains 4451139 gr. Privi2756.2Better Load
45 grains 4451139 gr. Privi2839.17 Consistent
47 grains 4955139 gr. Privi2935.92Awesome=WARM!
41 grains 4451140 gr. Trophy2494More Consistent
44 grains 4451160 gr. Hornady2647.27Nice
46 grains 4955160 gr. Hornady 2754.5 Nice WARM!

The 270 Bullet has been around for a long time and is used by many hunters. The rifle used is a Remington 721. This is another round that has benefited from improved bullets and powders. These Enduron powders show a great deal of promise in this round. There is a good selection of bullet styles and weights.

270 IMR Enduron Powder Loads

60 grains 445190 gr. Sierra HP3656.25WARM!
60 grains 7977130 gr. Speer2876Slow
56 grains 7977130 gr. Speer2876Slow
59 grains 7977140 gr. Nosler2880Consistent
58 grains 7977150 gr. Hornady2761 Nice Load
60 grains 7977 150 gr. Hornady2965.33Very Consistent

The 7 mm-08 is a versatile round well worth having. I purposely left some of the loads sitting in the sun until they got so hot it was hard to load them. I wanted to see if there were any spikes in the loads and none were evident so the claim that it isn’t heat sensitive has some merit. I did that with some of the 30-06 loads also. Like any other rifle, loads should be approached from below and carefully worked up. Each rifle is unique and so are the loads.

7mm-08 IMR Enduron Powder Loads

45 grains 4166 100 gr. Sierra HP3156Good Load
41 grains 4166120 gr. Hornady Flex2943.27OK
45 grains 4451140 gr. Sierra BT2746.83OK
46 grains 4451154 gr. Hornady 2666Nice
44 grains 4451162 gr. Hornady2580.22Good Load
44 grains 4451162 gr. Hornady (backwards)2596.17Decent
45 grains 4451162 gr. Hornady2683.11WARM!
43 grains 4451175 gr. Hornady2546.78Nice Load

The 7 X 57 Mauser has been around for many years and is one great round with a strong gun and modern loads. There are some older rifles out there that should avoid max loads. The model 93 that has the rolling block, although a good gun, should not be used with max loads.

The gun used in this test is a model 98 that was re-barreled so heavy loads can be used. With top loads, it is capable of a lot of large game hunting and with the great selection of bullets that is enhanced. These loads should not be exceeded and in a weaker gun such as a 93 should be cut down by at least 2-3 grains.

The 175-grain load was way too hot and blew one primer and the rest shows definite signs of excess pressure. As odd as it might seem the load was outstanding in regards to consistency. ES of 43 and an SD of 16 which is really consistent.

Going through my records I have found that loads that may be too warm to use have a good es and sd though not always. The barrel on the test gun is 26” long which definitely adds to the velocity and should be factored in when determining how good the load is.

7 x 57 Mauser IMR Enduron Powder Loads

47 grains 4166120 gr. Sierra3073MAX - Consistent
45 grains 4166139 gr. Hornady2931Nice Load
48 grains 4451154 gr. Hornady2761WARM!
47 grains 4955160 gr. Sierra2712.75MAX - Nice
46 grains 4955175 gr. Hornady3578.3MAX - Very Consistent
49 grains 4955175 gr. Hornady 2671Too Hot!

The 7 mm Remington mag was tried with two of these powders.

The 7 mm Remington mag which came out in 1962 is the most popular belted case. There are a couple of reasons for that. Especially with the new and improved bullets, it can handle almost any hunting situation. Recoil isn’t excessive while accuracy is very good with most loads. Components are readily available which is another plus with this round.

At a later date, as time permits, I plan on some more work with this round as I feel that more performance can be realized. In addition, there is published data on this round.

Pair of 7 mm Rifles
Pair of 7 mm Rifles

7mm Remington Mag IMR Enduron Powder Loads

68.5 grains 4451100 gr. Sierra HP3396Fair
65 grains 4451120 gr. Hornady3322.22OK
71 grains 7977 140 gr. Privi3094.89Consistent
71 grains 7977145 gr. Speer3018.92OK
71 grains 7977154 gr. Hornady2971Mild
67 grains 7977174 gr. Privi2818.78OK
67 grains 7977175 gr. Hornady2794.62Consistent
68 grains 7977175 gr. Hornady2899.7Decent

7.35 Carcano was brought out in 1939 by Italy. Due to the start of WW-II, the Italians went back to the 6.5 and sold most of the 7.35 rifles to Norway. It takes an odd diameter bullet usually .298 and the 4166 seems to work well in it.

7.35 Carcano IMR Enduron Powder Loads

38 grains 4166122 gr. Milt2431High ES
39 grains 4166122 gr. Milt2453More Consistent
36 grains 4166150 gr. Speer RN2214High ES
37 grains 4166150 gr. Speer RN2223Better than 36

The 30-30 has been around forever and no test would be complete without it. So we used four different bullet weights with 4166. The 4166 is definitely a viable powder in this chambering. The 4166 is the fastest burning powder and along with the relatively small case they make a perfect match.

Note the difference that a single grain can increase results. That is why when working with a new powder it is prudent to be cautious.

30-30 (bottom) next to 7.62 x 39
30-30 (bottom) next to 7.62 x 39

30-30 IMR Enduron Powder Loads

35 grains 4166125 gr. Sierra2532.78Consistent
33 grains 4166 150 gr. Hornady RN2344.83OK
32 grains 4166160 gr. Flex Tip2284.36Decent Load
31 grains 4166170 gr. Speer2151.83Fair
32 grains 4166170 gr. Speer2238.79Nice Load
31 grains 4166 180 gr. Hornady RN2045Consistent
32 grains 4166180 gr. Hornady RN2251.18Nice Load

The 30-40 Krag was introduced in 1893 and continues to be used for hunting and target shooting. Since it has limited strength caution is advised when working with the top loads. A long barrel 28” was used for these tests.

30-40 Krag (bottom) and 303 British
30-40 Krag (bottom) and 303 British

30-40 Krag IMR Enduron Powder Loads

46 grains 4451180 gr. Sierra RN2401Very Consistent
46 grains 4451180 gr. Sierra BT BKS*2356Consistent
46 grains 4451 180 gr. Sierra BT2344High ES
48 grains 4955180 gr. Sierra RN2532.67Very Consistent
44 grains 4451 200 gr. Speer2159OK
42 grains 4451220 gr. Sierra RN2126Mild High ES
45 grains 4955220 gr. Sierra RN2286Nice

**The 180 grain Sierra BT soft point loaded backward was much more consistent then loaded normally. I have found that in a couple of other instances. I don’t have an explanation for that.

The 7.5 X 54 French Mas round was used during WWII as it replaced the 8 X 50 Lebel.

The bolt action rifle is well made though the locking lugs are located in the rear of the bolt, an uncommon feature. There is some military ammo available but it seldom goes off. All of it I have acquired ended up having the bullets pulled. Brass is available from Privi and it takes standard 30 caliber bullets. If you can’t find the brass then 6.5 X 55 Swedish can be necked up and shortened.

Power wise it is the equal of the 308 which makes it a very useful hunting round. These loads equal most 30-06 loads which would indicate excess pressure. However, there are no obvious signs of stress but I strongly recommend starting at least 2-3 grains below and carefully working up. Upon closer inspection and work it was found that the cases were harder than normal to size which can be an indication that the loads are too hot. That along with the excess velocity should give us pause. The primers were a little loose but not enough to throw away. Measuring cases show some expansion but since they were new cases it is an indication but along with the other signs caution should be the procedures used.

7.5 X 54 French Mas IMR Enduron Powder Loads

46 grains 4166150 gr. FMJ2788.92Nice
49 grains 4166150 gr. FMJ2947Consistent - WARM!
45 grains 4166165 gr. Privi2714Consistent
46 grains 4166180 gr. Hornady2763.91Nice - WARM!
46 grains 4451180 gr. Hornady2397.08Mild

The 7.5 X 55 Swiss is a good candidate for this powder and bullets.

Case capacity is very close to the Russian so the same loads will be used. These are high-quality rifles though they are a straight pull design. The earlier version came out known as the model 89. It has a slightly shorter case and loads are much lighter as the locking system isn’t as strong as the newer models. These loads are for the new models and shouldn’t be tried in the model 89. With the top loads work up carefully from below. The loads listed as hot are for information only and should not be used. That applies to all calibers.

7.5 x 55 Swiss IMR Enduron Powder Loads

45 grains 4166150 gr. FMJ2830Nice
47 grains 4166150 gr. FMJ2944Very Consistent
43 grains 4166 165 gr. Privi BT2614.37OK
46 grains 4166165 gr. Privi BT2838.5 Nice
50 grains 4451180 gr. Sierra2687.7Consistent
53 grains 4451 180 gr. Rem2668WARM!
52 grains 4955180 gr. Rem2678.36Consistent
52 grains 4451 200 gr. Speer2668Hot!
48 grains 4451200 gr. Speer2543.1Nice
50 grains 4451 220 gr. Sierra 2365Too Hot!

I would recommend that all of these loads be dropped at least 2 grains. All show signs of pressure and excess velocity. It was hot during testing which would be a factor but still dropping 2 grains would be a good idea. I hit the jackpot with the 150 and 165-grain loads using 4166. I have been finding that it is a top powder for these cases in regards to velocity and consistency. The 4451 is a great powder for the heavier bullets showing good results. Again do not use the loads that are listed as warm or hot. It isn’t necessary or safe and the loads are listed for information only. As much as I like 4895 the 4166 is as good or better in a lot of loads. No pressure signs were observed in the good load listings.

The 308 has been around since 1950 and we have two different semi rifles to test.

Both rifles were consistent with that load though they were near max. I have a Ruger model 77 which should enable us to get the most out of the 308.

*Bolt action rifle loads*

308 IMR Enduron Powder Loads

46 grains 4166150 gr. Sierra *2934Consistent
41 grains 4166150 gr. Privi2519 GarandOK
41 grains 4166150 gr. Privi2508 LAR 8 Consistent
41 grains 4166150 gr. Privi2479 FAL Consistent
42.5 grains 4166150 gr. Privi FMJ2752.4Rock River LAR-8
42.5 grains 4166150 gr. Privi FMJ2717.89M1-A Springfield
44 grains 4166165 gr. Hornady *2776.1 Consistent
43 grains 4166180 gr. Sierra2562.78Nice
42 grains 4166180 gr. Remington *2671.1High ES
41 grains 4166 200 gr. Speer2372.3Consistent

The 30-06 is the most versatile round in existence so there will be a lot of info as all four of the powders will work for something though may not be the ideal powder such as the 7977.

The slowest is 7977 which will be suitable for various large magnums. I am trying one load in the 30-06 but I suspect that it will be too slow to produce max velocities with a 220 grain. It would indicate that this powder is a bit slow in the 30-06 even with a heavy bullet. If you can drop tube in a couple of grains more that might help but it would be a time-consuming effort.

The Garand load is close to what I want. For the Garand, I used military brass. The ES was somewhat high in the Garand rifles but a little tweaking of the charge will resolve that. They fed and cycled perfectly with no signs of excess pressure. With the 165, 180, and 200-grain loads I used commercial brass but, it was once fired of various brands and I didn’t sort it out, just made sure it wasn’t too long. The loads are very promising as the velocities are really good and they are consistent. I didn’t see any signs of excess pressure and they extracted perfectly. I will test them in other rifles to verify the results. I am running a second test with the 165, 180, and 200-grain bullets in a different rifle but with the same brass to check for pressure signs. Two stars (**) indicates the second test.

The second rifle was a 03 Springfield with a 24” barrel. The results are similar to the first test and some loads showed signs of pressure and these loads should be approached with extreme caution. Start from 2 to 3 grains below and carefully work up. I did not have any problems with sticky extraction with any of the loads but in other rifles that may very well occur. I did not look at any data before I started this project with the thought that it would help me get a good idea on how these powders perform. Afterward, I checked some tables and my results were close to the book loads. In some instances, these powders will produce a little extra velocity.

**Caution Reloading is dangerous, read our “Reloading Disclaimer“. The load data published by this website is intended discussion purposes only. You have been warned.**

30-06 IMR Enduron Powder Loads

48 grains 4166150 gr. FMJ 2613.3 Tanker Garand 18"
48 grains 4166 150 gr. FMJ2623.67Garand 24"
48 grains 4166 150 gr. FMJ2727.09Nice
49 grains 4166150 gr. FMJ2854.3Consistent
50 grains 4166150 gr. Sierra3014.92Very WARM!
51 grains 4166150 gr. Sierra3055.75Hot!
57 grains 4451 165 gr. Hornady2901.7Nice Load
57 grains 4451165 gr. Hornady**2895.08Consistent M-12
56 grains 4451180 gr. Hornady2779.75Consistent
56 grains 4451180 gr. Sierra 2807.83Very Consistent
56 grains 4451180 gr. Hornady**2860.56Hot!
56 grains 4451180 gr. Sierra**2857.7Very WARM!
64.5 grains 7977180 gr. Remington2726.5Not what I expected
55 grains 4451200 gr. Speer2657.1Good Load
55 grains 4451200 gr. Speer **2737.89Nice - Max
61 grains 7977220 gr. Sierra2379High ES
54 grains 4955220 gr. Sierra2527Nice - Max
57 grains 4955220 gr. Sierra2639.42Still Too Hot!
61 grains 4955 220 gr. Sierra 2786Way Too Hot!

***The 4955 will probably be more suitable for the 220 and heavier bullets, rather than the 7977.The 61-grain load is much too hot and under no circumstances should be used. The primers were blown out and there are prominent ejector marks on the cases. The 54-grain load with the 220 is absolutely the max that should be used. It shows very slight pressure loads in the Blaser used so I would drop down a grain or so in another rifle. Over 2500 is definitely on the high side for a 220-grain bullet. With the 4955 and the 220-grain bullet, I would strongly recommend starting at 51 to 52 grains. As always each rifle will react differently to the same load.

The 300 Win mag has been around for over 50 years and continues to be popular and a couple of these powders should work well in it. Due to some published information, I did not spend a lot of time with this round though I have no doubt the the proper

Due to some published information, I did not spend a lot of time with this round though I have no doubt the the proper Enduron powders will perform very well.

300 Win mag IMR Enduron Powder Loads

81 grains 7977165 gr. 3084.09Consistent
76 grains 7977180 gr. 2882.18Mild

The 4166 is the fastest of the four new powders so will start there for loads of 7.62 x 39. I didn’t see it listed for this powder but I thought it may work with this load. I was surprised in the velocities as they were higher than I expected. Loads functioned action perfectly. I was skeptical of the results as they produced more velocity then I expected so I did them again and even used a different chronograph.

* Second test. So it appears that this powder would be a viable alternative with the heavier bullets.

7.62 x 39 IMR Enduron Powder Loads

27 grains 4166150 gr. Privi1949Workable
27 grains 4166150 gr. Privi1936*Consistent
26 grains 4166 174 gr. Hornady RN1896OK
26 grains 4166174 gr. Hornady RN1776*OK

The 30 Harrett is a cartridge for a single shot handgun. Since it has a capacity very similar to the 7.62 X 39, the thought was to try similar loads in it. Since it has a shorter barrel the velocities will be lower. Cases are formed from 30-30 brass, as there is no factory fodder available. The results were surprising and especially the 165 which has a SD of 8.96 which is exceptional. The velocities are very similar to the 7.62 X 39 considering the 39 has a longer barrel. Either would make a decent deer gun at closer ranges.

30 Harrett IMR Enduron Powder Loads

28 grains 4166150 gr. FMJ1881.38 Nice
27 grains 4166165 gr. Privi1850Very Consistent
27 grains 4166170 gr. Speer1793.22Fair
26 grains 4166180 gr. Hornady RN1745.62Real Consistent

The 7.7 Jap served during WW-II and is still fairly common today. With that thought tried some 4451 in it. It takes the same diameter bullet as the 303 British and 7.65 Mauser rounds. With good loads and bullets, it is close to the 30-06 in power and has a good enough bullet selection to make it versatile. If you want a heavier than normal bullet Hawke makes them in 190 and 220 grain RN types. These powders seem to bring out the best in the Jap round. Without much doubt, I can get a little more velocity but I don’t see the point in stressing an old rifle just to get a few feet per second more. These loads are adequate for most hunting situations. Note the difference in the 49 and 50-grain loads. They were done on different days but temps were similar so I would consider 50 grains to be a max load although there were no pressure signs.

7.7 Jap IMR Enduron Powder Loads

50 grains 4166123 gr. Hornady3239.78Nice
50 grains 4451150 gr. Sierra2711Good Load
50 grains 4451150 gr. Hornady2727.62Consistent
48 grains 4451174 gr. Hornady2376Mild High ES
49 grains 4451174 gr. Hornady RN2365Mild
50 grains 4451174 gr. Hornady RN2648.89Real Consistent

The 7.62 X 54 Russian has been around since 1891 replacing the Berdan round. It has the advantage of a plentiful supply of rifles at very reasonable prices. Many countries used them and they are still used in some of the backward countries. Ammo and brass are relatively easy to obtain so you are in luck. It has approximately the same power as a top end 308 and is capable of good accuracy. It might not be a bad idea to slug the barrel as I have seen some go from .308 to .316 so in order to get the best accuracy use the correct diameter bullet. Factory ammo usually has a .310 diameter slug. I would not recommend increasing the top loads.

7.62 X 54 Russian IMR Enduron Powder Loads

51 grains 4451180 gr. Speer RN2372 Consistent - Mild
53 grains 4451180 gr. Speer RN2455Nice Load
52 grains 4451 200 gr. Speer2416Good Load
50 grains 4451 220 gr. Sierra 2317 Very Consistent
The 303 British round with a 150 gr Barnes a winning combination.
The 303 British round with a 150 gr Barnes a winning combination.

The 303 British is one of the most widely known military rounds so the 4166 should be a good powder in it. The 303 came out in 1888 with a compressed load of black powder and a 215-gr FMJ RN bullet. In a few years, however, they went to Cordite and a lighter spitzer bullet. Today the 303 is still widely used by collectors and in some backwoods countries, it still can be used.

The 303 British is one of the most widely known military rounds so the 4166 should be a good powder in it.
The 303 British is one of the most widely known military rounds so the 4166 should be a good powder in it.

303 British IMR Enduron Powder Loads

45 grains 4166123 gr. Lapua FMJ2856.44Consistent
45 grains 4166123 gr. Soft Point2836.67Consistent
43 grains 4166150 gr. Sierra2702.3Decent Load
40 grains 4166174 gr. Hornady FMJ2449.3Nice
40 grains 4166180 gr. Speer2450.08Consistent

The 7.65 Mauser is another fine round and one of the earlier smokeless powder rounds. It came out in 1889 and was used by various countries and the 91 Mauser was an early rifle that used it. Later the model 1909 came out with it. The 1909 is a model 98 Mauser and was considered one of the best Mausers ever made. It uses the same projectiles as the 303 British and the 7.7 Jap. The top loads with the 150 and 174 are very consistent but should not be exceeded. There was a big difference between the Hornady 174 grain RN and the FMJ. While that is a larger than normal spread between bullets of the same weight it reminds us to finalize a load with the exact bullet that will be used such as a serious hunting load. You can also observe the difference that a grain or two of powder can make. That is why there are cautionary notes all through this piece.

Mauser model 91 in 7.65 X 53 another good choice for Enduron powders
Mauser model 91 in 7.65 X 53 another good choice for Enduron powders

7.65 Mauser IMR Enduron Powder Loads

50 grains 4166123 gr. Flex Tip3079Consistent
46 grains 4166150 gr. Hornady 2478.09Mild
48 grains 4166150 gr. Hornady2891Nice - Max
44 grains 4166174 gr. FMJ Hornady2225.9Mild
44 grains 4166174 gr. Hornady RN2641.5Nice
46 grains 4166174 gr. FMJ Hornady2717Consistent - Max

Sometime between 1890 and 1900, Germany brought out the 8.15 X 46. It is a German version of the American 32-40 both in power and use. It was popular for 200-yard matches because of it good accuracy and low recoil. Bullet diameter is usually .318 though slugging the bore might not be a bad idea. I have made ammo for several of them including one that I owned. Cases are made from a 30-30 or 32-40 brass that needs to be trimmed and sized. Some of the older guns were originally designed for black powder and caution should always be used. Some 98 Mausers were rebarreled to this round and can safely utilize modern type loads. Due to the small case power being limited it would barely be adequate for deer with the best loads at close range. It is however, an enjoyable round to shoot due to its light recoil and good accuracy. For the Mauser, I had to dress down the rim in order to make them fit. It was only a small amount but, using a drill and file was time-consuming.

German 8.15 x 46 IMR Enduron Powder Loads

32 grains 4166125 gr. Hornady2397.2Decent
30 grains 4166150 gr. Hornady2296.27Fair
28 grains 4166 170 gr. Hornady .3182029Nice Load

The 8 X 50 Lebel can benefit from mild loads especially the model 86 used in this test. It has a tubular magazine which prohibits using pointed bullets so I have loaded one backward. With bullets loaded backward you can’t use compressed loads as the bullets go in crooked so that is a limitation we have to live with. That applies to all of the rifles I have tried. A little shopping can produce bullets from 125 to 220 grains so almost everything is covered.

8 x 50 Lebel IMR Enduron Powder Loads

52 grains 4166150 gr. Hornady2951.4Consistent
51 grains 4166170 gr. Hornady RN2159Very Mild
48 grains 4166175 gr. Privi backwards2687.55Very Consistent
45 grains 4166174 gr. Privi backwards2140Mild
45 grains of 4166198 gr. Privi FMJ2491.09Fair

The 8 X 52 Siamese Mauser came out in the 1920’s to replace the older 8 X 50. A modified Mauser 98 was used for this round. Since it is a large rimmed round the action had to be modified to accommodate this chambering. There is no ammo or brass available so 45-70 cases or 8 X 56 cases which I used. They have to be modified to be usable. There are a couple of commercial ammo makers who will make the brass or sell loaded ammo. Once you have the brass and dies loading is typical and it uses a standard 8 mm bullet. Since it is a 98 action good loads can be developed giving it adequate power for hunting.

8 x 52 Siamese
8 x 52 Siamese

8 X 52 Siamese Mauser IMR Enduron Powder Loads

45 grains 4166150 gr. Hornady2654Mild - Consistent
47 grains 4166150 gr. Hornady2731.5Nice Load
45 grains 4166175 gr. Privi2540.4Very Consistent
45 grains 4451198 gr. Privi FMJ2193.33Mild
Ammo for the 8 x 56 Straight Pull
Ammo for the 8 x 56 Straight Pull

The 8 X 56 straight pull came out to replace the older 8 X 50 both use the model 95 straight pull rifle.

For some reason, they use a .330 diameter bullet instead of the regular .323 bullets. That makes it more difficult to get bullets though they are available. Privi does make the brass, so with a set of dyes you are in business. The round has enough power for most hunting and the rifle is well made. Personally, I don’t care for straight pulls but they function well and gives the owner an opportunity to build up their arms. Like some of the other military guns tested the velocities seem higher than normal. That may indicate excess pressure but none were present during testing. I would strongly advise starting 2-3 grains below and carefully working up. The barrel is short 18” so velocity would drop some as a result.

8 x 56 Straight Pull IMR Enduron Powder Loads

52 grains 4166150 gr.2717.18Consistent
50 grains 4166175 gr. 2563Nice Load
48 grains 4166205 gr.2395.27Nice - WARM!

The 8 X 57 Mauser is one of the most common military rounds which came out in 1888 in the Commission rifle. The model 88 isn’t a Mauser action and is inferior to the 98 action. It also uses a .318 diameter bullet so if this data is used start at least 10% below the listed loads. I have a Commission rifle and at a later date will develop some loads for it. In 1904, the Mauser went to the .323 diameter bullet which is used today. Components are plentiful and easy to get. In a model 98 loads can be developed that will get the most out of this round. With top loads, it is close to a 30-06 in power. These loads should not be used in a Commission rifle. These loads should be reduced from 10 to 15% at least for use in a Commission or other weaker rifle.

8 X 57 Mauser IMR Enduron Powder Loads

52 grains 4166 125 gr. Hornady3245.45Nice
50 grains 4166150 gr. Hornady2955.75Real Consistent
47 grains 4166175 gr. Privi2713.81Nice
46 grains 4166185 gr. Remington2575.7Good Load
44 grains 4166198 gr. FMJ2454.75Consistent
45 grains 4451220 gr. Sierra2304.91Consistent

The 32 special came out as a companion to the 30-30. The idea was it was supposed to be usable with black powder, which was still common when the 32 was introduced. Unlike the 30-30, it never became very popular though it will do well in hunting deer in the woods. There are not very many bullets suitable for it though the 170 does just fine.

32 Special IMR Enduron Powder Loads

35 grains 4166170 gr. Speer2201Nice Load

The 358 Winchester has been around since 1955. In spite of the fact that it is a terrific hunting round it has never been really popular. During various time frames, a couple of companies made rifles. For this test, a Browning lever rifle is being used. It was bought in 1977 and has harvested many deer through the years. Like the 35 Whalen, it is flexible with the ability to use 38 caliber handgun bullets at reduced velocities. Later on, when I get a bolt action rifle in this caliber will resume testing as this is a much better round than sales figures indicate.

Testing the 358 Winchester
Testing the 358 Winchester

358 Winchester IMR Enduron Powder Loads

50 grains 4166180 gr. Speer2536.51Nice
48 grains 4166 200 gr. Hornady SP2132Surprise Slow

The 35 Whalen has been around and should do well with a couple of these powders. With good loads, the Whalen would be adequate for almost any large game. If you don’t like belted cases but want some serious punch this might just be the round that you are looking for. For light loads, 357 bullets are just the ticket. It is an extremely flexible round especially for the handloader.

35 Whalen IMR Enduron Powder Loads

58 grains 4166180 gr. Speer3000.36Nice
60 grains 4451200 gr. Hornady2610.8Mild
58 grains 4451250 gr. Hornady2436Mild

The 38-55 is an old round originally loaded with black powder. Happily, they have made some modern strength guns that can take advantage of the round. I have an H & R single shot, which allows the use of bullets not suitable for a lever gun and modern loads. The IMR 4166 may be on the slow side but will be interesting with heavier bullets. In modern type guns, 4166 is a viable powder.

38-55 IMR Enduron Powder Loads

38 grains 4166 200 gr. Sierra2073Nice
38 grains 4166200 gr. Sierra (2nd test)2113Consistent
37 grains 4166220 gr. Hornady2094.11Consistent
36 grains 4166235 gr. Speer1947Nice Load
35 grains 4166245 gr. Cast1925OK
34 grains 4166250 gr. Hornady1963.7 WARM!
I have an H & R single shot, which allows the use of bullets not suitable for a lever gun and modern loads.
I have an H & R single shot, which allows the use of bullets not suitable for a lever gun and modern loads.

**Caution Reloading is dangerous, read our “Reloading Disclaimer“. The load data published by this website is intended discussion purposes only. You have been warned.**

About Bob Shell:

A Custom Reloader of Obsolete and Antique Ammo, Bob Shell, writes about the subject of Guns, Ammo, Shooting and Related Subjects. Visit: www.bobshellsblog.blogspot.com.

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So I just finished working my loads up for my 7.5 swiss, but I used 4451 with the lighter bullets. Now I’ll have to give it a go with the 4166 and see which one works best as far as accuracy. I’d seen 53gr of 4350 as a published max for 150gr bullets in the swiss but had no problems getting there with 4451. All things equal, id get 15ish more rounds per pound with the 4166. I’m not sure what good is yet, but I was beating the PPU ammo so it couldn’t be that bad.


It would be nice to see want the new IMR powders would do for the 375 WBY MAG.

Willard Walker
Willard Walker

Sorry about the misspelled words Siri went back to original interpretations it was not supposed to be Dovehunt it was supposed to be to hunt with and crown oh was supposed to be crono other corrections doubled up at times I apologize for the errors and the hard reading.

Willard Walker
Willard Walker

My name is Willard Walker and I am trying to find some good loads for .300 Savage with monolithic bullets for hunting in California. I am relatively new to re-loading Doing so for only the last two years. I have a copy of the Lee modern reloading manual that I have used as a guide to reload. I have not experimenter much beyond the published info but am beginning to as I become more confident in my abilities. I measure each powder charge religiously and keep data on The data I can obtain. I do not have a crown oh… Read more »


I use baking soda, makes for a nice cloud similar to what old black powder is like.


When’d Duron quit selling that ‘other powder’? Was that after Obama commuted his sentence?


Why go from 55 to 90 grain bullets in 223? Most are loading the 69 and 77 grain now. Would have been nice to see results with those weights.

Jim Macklin
Jim Macklin

DO NOT, stuff foam rubber into a cartridge case as a filler unless you want to blow up the gun.
The old school filler to use in straight walled cases was cream of wheat, or kapok from an old dried life preserver. Modern use would be a few fibers of dacron fiber [pillow stuffing].

Best thing is to use a proven and tested powder that fills the case to 80% volume.

Wild Bill
Wild Bill

@Sailboatbum and Jim Machlin, Ok, negative on the foam rubber. Find some kapok! Roger that. Out


Great article. Just be careful with many of these loads. When loading with reduced loads I always use a filler to keep the powder on top of the primer. In a straight walled case I use a thin disk of heavy paper but in bottle neck rounds I use pillow stuffing. This keeps the powder from lying in the case with an air gap on top. This keeps the primer from igniting all the powder at once and increasing pressure. Just my own little safety precaution. Enjoy, Sounds like some great powder.

Wild Bill
Wild Bill

@Sailboatbun, Pillow stuffing! Do you mean foam rubber? What a great idea.


Kapok is what I was talking about. Sorry I am from the old school.
well over70. Used to buy it at the dry goods store. One bag would last
many years.

Willard Walker
Willard Walker

I always wondered why my grandfather used a little bit a corn meal on top of a black powder charge some times in a old 44-40 thanks for the info.

Jim Macklin
Jim Macklin

Nice to see new powders with some data that is not generally included in most manuals. I did see one thing that bothered me. “Editors Note : Caution, Reloading is dangerous, read our “Reloading Disclaimer“. The IMR Enduron Powder load data published by this website is intended discussion purposes only. As with all data collection, mistakes are possible. You have been warned.**” Reloading CAN be dangerous, it can also be very safe. Wearing safety glasses is the first absolute safety measure. Having static control to prevent accumulation of static electricity can prevent problems. Static charges might also be a cause… Read more »