Tom schools us on how to install an M203 Grenade Launcher on your AR15 or M16 rifle.
USA – Did you know you can add your very own M203 Grenade Launcher to a rifle you already have? Here, we’ll show you mounting options and exactly how to do it.
The installation process shown here is for a standard M16A2 20-inch rifle barrel with a .625” outside diameter. If that’s not your rifle, no worries, there are additional mounting options for M4 carbine barrels using a GI-type barrel nut at the rear. You buy the LMT M203 unit separately and then choose the right mounting kit option from the following choices.
M203 20-inch Mounting Kit with Leaf Sight
The “standard” original mount replaces the triangular handguard with black polymer versions containing internal aluminum heat shields. This model installs completely behind the A2-style gas block and front sight housing assembly and requires a rifle with the standard mil-spec barrel nut. The replacement handguard comes with a leaf sight. We’ll walk through the installation steps in detail in a minute.
M203 Carbine-style Mounting Kit with Leaf Sight
If you have a more recent M4-type rifle that uses or has a circular front cap and the .625″ outer diameter cutout just ahead of the gas block, then a carbine-style mounting kit is what you need. Like the 20-inch barrel mounting kit, this one also comes with a leaf sight and replaces the whole handguard assembly.
M203 Quick-Detach Mounting Bracket
This component is not a complete mounting kit but rather an add-on to either of the rifle or carbine mounting kits that allows quick attach and detach of the launcher.
M203 Grenade Launcher Installation
I found that the installation of the M203 launcher on the Brownells BRN-601 was straightforward once I found the instructions. While a simple process, it did require a bit of muscle and brute force at times, so an extra pair of hands might help.
Since the launcher replaces the handguard, the first step (after making sure the rifle is unloaded!) is to remove the standard triangular handguard from the BRN-601 AR-15 rifle. Technically this doesn’t require tools, but a handguard removal tool will really help as the spring under the delta ring is under some pressure. I didn’t have one and relied on muscle power, so it’s doable either way. Just pull the delta ring towards the receiver enough so that you can rotate the base of the handguard out from underneath. Once you do that, the handguard simply pulls out of the triangular support behind the A2 gas block and sight housing.
Now that the barrel is exposed, you can slide the front mounting bracket into place. There’s a polymer collar that protects and insulates the barrel. It’s a bit tricky to seat the two halves of the spacer inside of the metal bracket when you get to attaching the M203 to the bracket, but persevere, the end result is worth it.
This “U” clamp provides the hard mount for the M203 Grenade Launcher at the forward end. At the rear, the launcher slides into the barrel nut.
The trigger guard on the M203 Grenade Launcher swivels around a forward mounting point but has no rear anchor. For that, the unit relies on the lip of the magazine well. The steel guard has a bit of flex, and you have to compress it slightly so that a notched area compresses against the lip of the magazine well. That’s what keeps the trigger guard closed. You’ll need to make sure the trigger guard is in place before completing the next step of bolting the M203 to that forward “U” clamp around the barrel.
As you insert the rear of the M203 Grenade Launcher into the barrel nut area, while taking care to make sure the trigger guard us positioned against the mag well properly, you’ll rotate the forward end of the M203 to mate with the barrel “U” clamp.
The M203 has a hard ledge that butts against the clamp, so you might have to apply some muscle to get everything seated. I had to bend the trigger guard ever-so-slightly to make everything fit properly, so be prepared for that.
The mounting kit comes with a section of steel wire. That’s the double-secret-mount insurance. The bolt that attaches the M203 to the forward “U” clamp has holes in the head and nut on the opposite side. Run the wire through the bolt head about half way and then start twisting the two wire ends together tightly against the bolt head. Continue this twisting until just enough of the wire is a two-strand “rope” to reach around the front of the M203 Grenade Launcher to the nut on the opposite side. Run one end of the wire through that nut and resume twisting on the far side for maybe another inch. Clip the excess and tuck it away around the back of the mount, so it’s out of the way. It sounds complicated so refer to the pictures here. All of this provides a bit of security against the bolt loosening and the forward section of the mount disconnecting.
At this point, you have a fully mounted launcher, but with no handguards. The replacement black handguards with aluminum heat shields install just like the originals you used in the first step. Insert the forward end of one handguard half into the front triangular mount while pulling the delta ring towards the receiver until you can seat the rear ledge of the handguard under the delta ring. Repeat for the other half. Again, you can do this by hand, but a handguard removal tool makes it a lot easier.
Last, install the leaf sight. This just screws into the top of the handguard. You can perform this step first if you like, I just found it easier to complete all the other steps without the leaf sight in the way. If you have to muscle any of the other parts, you don’t want to damage the leaf sight in the process.
The installation process for a carbine is virtually identical as the most significant differences are the length of the handguard and the circular front handguard mount. If you want to make an M203 a semi-permanent addition to your rifle, just use one of the standard mounting kits depending on whether you have the 20-inch rifle or a carbine. If you want quick-detach capability, be sure to order the M203 Quick-Detach Mounting Bracket.
About Tom McHale
Tom McHale is the author of the Practical Guides book series that guides new and experienced shooters alike in a fun, approachable, and practical way. His books are available in print and eBook format on Amazon. You can also find him on Facebook, Twitter, Instagram, and Pinterest.
Informative article! 40mm launchers aren’t illegal to buy, as long as you follow all NFA regulations and your state or local jurisdiction doesn’t ban them. I recently bought a M203 receiver which I will Form 1 into a registered Destructive Device. Non-explosive 40mm munitions (flare and smoke) can also be purchased and are not NFA regulated themselves, just the launcher.
Unless your with the cartels why? For the wannabes? I had one on my m16.
“The replacement black handguards with aluminum heat shields install just like the originals you used in the first step. Insert the forward end of one handguard half into the front triangular mount while pulling the delta ring towards the receiver until you can seat the rear ledge of the handguard under the delta ring. Repeat for the other half.”
.
What “other half?”
Interesting, I will never use the info, but it’s nice to know.
Just one silly little question: WHY?
Why not?
Why should a grenade launcher on an AR15 be made available to the general public in America? So you can blast glorious, shrapnel-filled grenades through the front doors of Muslim mosques and Jewish synagogues (and Catholic sanctuaries sheltering illegal Mexicans and AME churches brimming with Blacks), then, kneeling outside on a heretofore quiet neighborhood street, a safe distance back, empty your clips in a fiery spray of God’s breath raining down on any evil “survivors” who try to escape your dispensation of the wrath of the just and merciful Almighty God. With this wonderous addition, no longer is there the… Read more »
Quoting CNN doesn’t help your argument.
Most people buy the 37mm smoothbore replica grenade launcher which shoots flares, etc. A 40mm rifled real grenade launcher is listed by the NFA laws as a destructive device and is heavily regulated. moreover, you can not buy explosive shells for 40mm (or 37mm for that matter) at all.
You are an uninformed communist troll.
Zackley…. You can only get flares and smoke bombs, NEITHER work very well. More expensive novelty that anything. Gives the, as usual, misinformed leftist trolls a bitch point. Yeah, GeorgiePorgie has gone to the leftist creative writing center, guaranteed…
Leftists shouldn’t be allowed to own firearms, I mean they’ve been the shooters in all the mass shootings and muslims, they both have the same ideologies. They’re a danger to themselves and society, they really shouldn’t be allowed to vote since they can’t make responsible decisions.
@SG, He seems to be flying into a mental panic. I sure hope that he is not a danger to himself or others.
WB;
His head is so far up his ass it would take a team of proctologists a year to remove it.
I assume you’re kidding with that series of Hollywood/CNN iteration of ignorance. It is a flare launcher…no explosive grenades.
I think you’re over-exaggerating by a huge amount. These DO NOT use explosive rounds. Explosive rounds are illegal by law, and all 40mm launchers are also illegal to buy. These are 37mm launchers, and they aren’t used with explosives. I find it offensive you claim anyone who owns one of these, and possibly anyone who owns a gun in general, is a terrorist, and that everyone is a white supremacist that will shoot up mosques and synagogues. As I am an American Jew, it sickens me a ton to believe that someone thinks almost all Caucasians are terrorists.
“…and all 40mm launchers are also illegal to buy.”
Not true. 40mm M203 and M79 launchers and 40mm barrels registered under the NFA as Destructive Devices are legally transferable among civilians.
@GP, Why would you think those are the proper uses of those toys? Why do you hate your fellow Americans so much?
The source of leftists hate comes from their fear. Fear leads to anger… anger leads to hate… hate leads to suffering. I sense much fear in georgie.
P-L-E-A-S-E go back on your meds, PLEASE!!!
WOW. You gave us some good ideas we had not thought of. Thanks.
Sir, may I suggest you consider a dopamine receptor antagonist? Clozapine, asenapine, and olanzapine are all effective against delusional psychotic episodes and considered safe.
In the early 70s I carried the m16 with a an m203 grenade launcher. A devastating weapon.
@Darrell, We had M-79’s and I never touched one, but some guys were extremely accurate. But as Calvin above asked, why would anyone want one of these?
I never saw one of those in Vietnam. I came back in Jan 70. I’m just curious, were the rounds used in that the same as the ones used in the M79? I don’t see how the aluminium receiver of an M16 could take the punishment of the rounds we had for the 79. My shoulder is still hurting some 50 years later from shooting that thing.
As far as why, people like things that look like the real deal. My opinion.
While the M79s were common in the nam, the M203s were rare. Mostly special forces or combat trials. It was found that even though the M203 worked, every soldier doesn’t need to be a grenadier. The rank and file are better off with a lighter and easier to handle carbine. If grenades at range were needed, somebody in the platoon would have an M79 available anyway.
I guess their wasnt enough newsworthy material to publish so an instruction on mounting an M203 was added right before press time to fill up the pages. How many readers will benefit from this, 1% or less I would imagine. Why would any rifleman worthy of the title put this clunky forward weight on their AR and wreck the handling characteristics of their weapon just to fire an occasional flare or smoke round ? Im a practical guy. If I need a signal flare I use my flare pistol. If I need gobs of real smoke I pop a smoke… Read more »
We may be getting close to your scenario. That 203 is looking pretty good to me. As a company armorer. And using one in the military. It was not a noticeable obstruction for any rifleman worthy of the title as you say. Just another tool at your disposal. And quite effective if used properly. Added weight is always a trade off. Being a M1A1 Abrams tanker it was not so much a issue. Yes I was doing two different MOS at the time. A lot lighter than M240, M2HB. Being 21 yrs old & physically fit. The added weight was… Read more »
If the ATF hasn’t pounced on this yet, it will come soon especially if any of them are sold. Think bump stocks only worse.
I’d rather have an SBS under it..
a 3 round pump shottie is much easier to use tactically.