A .338 Federal AR-10 Rifle Named Thumper

By Nathan S.

Thumper - A .338Federal AR-10
Thumper – A .338Federal AR-10
AmmoLand Gun News
AmmoLand Gun News

USA –  -(Ammoland.com)- Thumper is my pride and joy, and now one of my all-time favorite rifles, named on its maiden hunt: an over-the-counter NM Black Bear license (I had to hunt something in 2015!)

The average black bear harvested in NM is between 150-225 lbs. I was over-gunned on this hunt. In dramatic fashion I witnessed Thumper earning its name.

Thumper started as a Christmas gift in 2014 when my brother gave me a stripped X-10 AR-10 receiver from VDC Armory LLC, and said we would build it however I wanted and with whatever parts I wanted to put on it. (Full disclosure – he owns VDC Armory and designs custom AR Rifles).

I thought on it a while and researched a caliber I thought would be something different and fun. I decided on building it as a .338 Federal. I called him up and told him my plan. There was a long pause on the other end. When he spoke he asked me if I was sure that could be put into an AR-10 platform and he would ask the Gun Smith details about that caliber.

They had not yet built anything chambered in .338 Federal, and why the heck did I want that? Well, just prepping for a dream if I ever make it to Alaska hunting.

.338 Fusion MSR
.338 Fusion MSR : http://goo.gl/Cp2bDn
Thumper - A .338Federal AR-10
Thumper – A .338Federal AR-10

After a couple months of casual searching I found an in-stock quality 18” .338 Federal barrel from JP Enterprise.

My brother called in a favor to Witt Machine & Tool and had a custom sized muzzle break (their Muzzle Rise Eliminator – MRE) made to fit the barrel.

We decided on a 15” Slim Quad style hand guard and Mission First Tactical furniture.

Soon Thumper was born (they use in-house “Birth Certificates” to describe a custom build. So it’s only natural to say Thumper was born.)

Next we discussed what hunting optic I needed. It is clear that the .338 Federal caliber is NOT a long distance caliber, so a high powered optic would probably be a waste of effort and money.

As my brother describes this caliber: “…within 400 yards its Thor’s Hammer. After that it is like calling in artillery…”

Thumper - A .338Federal AR-10
Thumper – A .338Federal AR-10 Rifle

Leupold & Stevens has been VERY supportive of our initial efforts with ARHunters.com and so we decided to try the Leupold 1x4x HOG Plex and their one piece scope mount. He told me their Armorer did NOT like test firing Thumper and described it kicking like a 12ga. I didn’t think a 12ga kicked that bad.

When I got it I thought the recoil was more of a push than a kick, and is rather enjoyable. I told you this is now one of my all-time favorite rifles. I broke in the barrel, got it zeroed, and was very happy with it. I was obliterating milk jugs of water at 300 yards in dramatic fashion.

Thumper - A .338Federal AR-10
Thumper – A .338 Federal AR-10

I plan on having Thumper with me on many hunts. I just need to get within 400yds.

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Read my Sheep Adventure with the Same Rifle

About the Author:

Nathan S. is an avid DIY Hunter, Massage Therapist & Healer, and Husband & Father. A Colorado Native who has lived and explored in AZ, AK, and NM. The wondering spirit has taken him across a lot of the western US; from winters in the desserts around Tucson AZ to the summers of the wide open Alaska. He is a top of his field Licensed Massage Therapist who has worked in some of the very best destination spas in the world. This has placed him between two very different world views and clarified his love of hunting. Nathan astutely studies the best odds for good Do-It-Yourself (DIY) Hunts in NM & CO. He has tagged a NM trophy bull elk with a Muzzle Loader from a unit that doesn’t always grow them to trophy class. His “The first priority is to fill the freezer” attitude is also laced with goals related to hard DIY hunts. He has taken deer, elk, pronghorn, & bear in CO and NM over his hunting career. The lessor known species he has taken are NM Javelina, a NM Ibex with a Muzzle Loader, and also chased NM Oryx that ended in tag soup. He continues to apply for tags of species he has not taken in NM and CO. You can find him with his family in tow often times with his daughter keeping pace with his hunting record (more about her soon). We expect Nathan to share some great DIY tips for ARHunters.com and keep Thumper working.

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I have a very ancient Winchester M94 30-30 I bought used in the early 60’s. I decided to buy a new M94 earlier this year. I suffered from extreme sticker shock! I decided to use an AR platform to replace it. I have built up a .458 SOCOM with a Vortex Spitfire AR 3X prism scope. I am very happy with the handling and accuracy out to 300yds. I will be hunting for Mule Deer in Central Arizona in heavy brush country.

Nick luneau

Any word on what his 338 fed cost minus optics?


We appreciate you all reading and commenting on the article.
I JUST got word that “Thumper” and ARHunters.com Staff Hunter Nathan S. just met some very well earned success on an Off Range NM Public Lands Oryx hunt in the July heat. It is a smaller broken horned Bull but when you work that hard to catch up with these Oryx you take what gets presented to you. I am sure we will get details of the hunt soon.

For the those interested in “other” AR Caliber choices of ARs please read the article we submitted here on the 243WSSM

Terry Davis

I didn’t know ‘thumper’ was trademarked. I built my THUMPER from a DPMS 338 lower that I got cheap and just couldn’t stand to put some other caliber upper on it (plus I wanted to test drive the 338 fed). I found an unused DPMS .338 federal barrel and installed it on a SAA upper (couldn’t find a DPMS at the time plus the SSA is an immaculate piece of gunmetal). I added a DPMS LR 308 floating tube and a Magpul ACS stock (cheekweld). All the other piece parts (except the Timmney modular fcg) are DPMS. For optics I… Read more »

Jim in Conroe

Well, it’s not exactly a trademark issue, but if you Google “Thumper Rifle” this comes up on Wikipedia: “The .450 Bushmaster is descended from the “Thumper” concept popularized by gun writer Jeff Cooper. Cooper was dissatisfied with the small-diameter 5.56×45mm NATO (.223 Remington) of the AR-15, and envisioned a need for a large bore (.44 cal or greater) cartridge in a semi-automatic rifle to provide one-shot kills on big-game animals at 250 yards. Inspired by this, LeGendre developed his .45 Professional cartridge,[when?] and later[when?] built and delivered an AR-15 in .45 Professional to Cooper. Bushmaster requested[when?] the ammunition manufacturer Hornady… Read more »

Terry Davis

I will yield to the grandmiester Cooper and totally agree with the inadequacy of the 5.56 round. I carried one for Mr Nixon many years ago. And I also hold all of the members of 450bushmaster.net in the highest esteem. (I have a 450 and it is INDEED a thumper). This being said, if Mr. Nathan S. wants to call his weapon of choice “el badassero de la gunnero” or anything else, I feel he should be allowed to without being ‘thumped”. Not saying, just saying!

Jim in Conroe

I yield as well.

I have decided to name my Thumper “Der Donnerschlagerblitzenmacher.”

Terry Davis

“The ThunderBatLightningDoer” Excellent Jim! Come on people – name your smokepole!

Jim in Conroe

Sorry, but Thumper is reserved for an entire class of AR platform guns, the Bushmaster 450.


Larry in Loomis

Thumper is good like my DPMS LR10 in 338 Federal with Larue quick release mounts and a Bushnell Elite 6500
4-30x50mm with mil dot. Shoots great and makes a big hole in White Tail. Got it for brush and larger game as you have said out to 400 yards. I am loading the Barnes TTSX 160gr bullet to try to reach 3000fps in the AR. Barnes list there max load for AA2230 at 53grs to 3095 fps. Will be testing them soon.