M4 Barrel Profiles and Forward Assists

40mm grenade launchers are NOT easy to get, they are classified as destructive devices and require an ATF Form 1.  Unless you talk to ABC news, you’ll find out that not too many people have them.

So why do so many companies make barrels with M4 profiles, if very few of us have M203 grenade launchers?

My theory is that a lot of people simply want their rifle to be very close to what the Military uses.   Whether or not they will be able to use aspects of the design is a moot point in their eyes.

Vuurwapen Blog has some great thoughts as usual (HERE)

Another good example of an aspect in design that few of us need, is the forward assist. Although I don’t shoot tens of thousands of rounds per year, I have never had to use it once and I’m sure most people can say the same.  Although I do occasionally see some n00bs at the range that repeatedly hit the forward assist with authority :roll: , after they seat a fresh mag and drive the bolt home.



Trent April 23, 2010 at 12:56 pm

I bought an M4 barrel profile because A) it was what S&W had, and B) I thought it looked “right”.

I realize it looks “right” because I see pictures of soldiers carrying real M4s all the time.

But I suppose it’s also possible to attach a 37MM canister launcher there, too, right?


Admin (Mike) April 24, 2010 at 12:41 pm

I think most of the 37mm launchers mount to a picatinny rail, not the way same as an m203.


Gun Nikhai April 23, 2010 at 01:18 pm

Well, I know why Californians do it. They have neutered, AR style rifles. If they want the goodies they have to go featureless. If they want a pistol grip, they have to compromise. When the only kind of black rifle you can own is a bastardized one, suffering the unending chortles from those owners living in more fortunate states….I can see the desire to have more ‘cool’ features to make up for it.

I suppose a better question might be…why do Californians need ‘bullet buttons’?


Admin (Mike) April 23, 2010 at 03:41 pm

ugh California gun laws make my head spin. Having to use a “tool” to drop the magazine is ridiculous. Glad that is stopping a majority of gangland shootings in the state though :roll:


Dixie April 23, 2010 at 10:02 pm

I have a forward assist, I don’t have a M4 profile barrel. To me, the M4 barrel looks like somebody let a guy on a three day bender work the barrel lathe. I’ve always wondered if the barrel heats and cools unevenly with all those different thicknesses.

The FA I like because it’s a little bit of insurance. Tap it with your thumb (once, with the thumb, not a dozen times with your palm) just to make sure the bolt’s locked.


Admin (Mike) April 24, 2010 at 12:46 pm

guy on a 3 day bender work the barrel lathe

Yea it almost looks like a ‘hold my beer and watch this’ type profile


cmblake6 April 24, 2010 at 01:52 am

Mall ninjas?


Admin (Mike) April 24, 2010 at 12:47 pm

The guys at the range? Yea most that do that seem to stereotypically wear 5.11 EVERYTHING.


Linoge April 24, 2010 at 08:03 am

I have a forward assist because when I was shopping around for uppers, slab-sides cost so much more than their FA counterparts that it was simply ludicrous to spend the money for nothing better than aesthetics – not that there is anything wrong with aesthetics, I just have a budget on it :).

As for the barrel, it is unlikely that the BATFE will ever permit me to own something in the 40mm range, so why bother?


Admin (Mike) April 24, 2010 at 12:49 pm

Yea its funny how less machining = higher price in this case. I guess the demand is lower though, so that’s why.


Bryan S. April 24, 2010 at 08:20 am

Finding an upper with no forward assist isnt cheap. Why anyonw would ever use one, I dont know. Maybe a leftover from the m1 days, where the extractor may no clear the rim and sit just out of battery… and the FA would be better than the idea of a broken hand from palming an M1 bolt forward into a slam fire (ouch!)

I know in my upcoming build, I am planning on not having it installed. Now if I could just find a 556 bull barrel……

@Linoge: its not so much getting the launcher.. its more getting the ammo ;)


Admin (Mike) April 24, 2010 at 12:54 pm

Is a bull barrel and an HBAR considered the same thing on a AR-15? Or are their bull barrels that are actually HUGE in diameter?


Fred April 24, 2010 at 11:57 am

If, for some strange reason, you ride the bolt forward and it might not fully lock, and you need something to nudge it forward.

I do agree that a 16″ barrel with an M203 cut does look silly.


Admin (Mike) April 24, 2010 at 12:56 pm

True. It’s too bad it wasn’t quieter when doing that, there is still that audible click. Albeit not close to as loud as the bolt slamming into the barrel extension as usual.


John M April 27, 2010 at 03:02 pm

In the event of it being slightly out of lockup, you can push the bolt (which of course is contoured) closed manually through the ejection port w/o the dedicated FA (assuming it’s not yet hot to the touch).


Admin (Mike) April 28, 2010 at 03:40 pm

Good call John. Like you mentioned there are some downsides to that method though.


miso neno May 7, 2010 at 01:43 pm

Most of us probably don’t care for the m203 cut on our ARs. Instead it’s more of an economic matter. Many of the inexpensive uppers on the market sell with the m203 cut. My real preference is proper pencil barrels or medium weight non-cut barrels but they’re generally harder to come by and cost a few

http://www.dsarms.com/DSA-ZM4-Forged-7075T6-A3-AR15-Upper-Receiver—DSZM4CBU/productinfo/DSZM4CBU/ $275 upper with the m203 cut.


Admin (Mike) May 8, 2010 at 12:17 am

Wow, $275 for an upper is ridiculously cheap.

Since I don’t carry my rifles around all day, I’d have to say I am more of a fan of the HBARs rather than the pencil/medium barrels that you said you like. I could definitely see wanting a reduction in weight if I had to carry a rifle for a living though.


Admin (Mike) May 8, 2010 at 12:19 am

Nice photography by the way! (I check out your site)


jeff June 16, 2010 at 04:46 am

i used my forward assist once after I did a press check and the bolt did not lock up.

I was delighted to have discovered the moment when I needed it and did the natural thing without thinking. :)


032125 August 5, 2010 at 03:58 am

I always thought that the 203 profiled barrels were prevalent simply because that is the military spec; therefore manufacturers are already set up to shape the barrels that way, therefore they are cheaper, therefore they are more common.

I think that the concerns about the barrel heating up and changing the zero are a ridiculous crossover concern from the precision shooting community. Barrel heating may matter if you’re trying to hit a target at 500+ meters but I’ve shot M4s in the military until the barrel was visibly glowing in the desert sun, and could still hit a human out to 200 meters. Sometimes the things that worry people astounds me.

I’ve also used the forward assist after a press check, but probably no more than twice in my entire life. At this point is probably a relic.


Alex November 20, 2010 at 11:05 am

Let me answer your question with another question: Why NOT have the forward assist? If you rifle is a range queen only, then sure you’ll never “need” it. But many people consider their AR their home defense/SHTF rifle, and there is a reason that the forward assist was added in the first place. I mean, what do you lose by it being on there? Weight? Looks? To me, the potential benefit of having it on their far exceed the “downsides.”

And FYI, there are some (although not even remotely close to all) units in the military who training to load a mag, tug to ensure it’s seated, send the bolt home, and tap the forward assist….EVERY TIME. This is especially good insurance for right-handed shooters who cannot physically see the bolt from their normal shooting position.

Now I do agree that the M4 barrel is a piece of crap…for my personal rifles, I choose to go either lightweight or HBAR (depending on the application).

– Alex


Admin (Mike) November 26, 2010 at 01:50 pm

Yea if the forward assist is there.. then whatever, I just wouldn’t pay extra for it though. I like my rifles to look authentic too… not having the forward assist would look like something is missing.

Interesting stuff on the military units being trained to tap the forward assist every reload. I wasn’t aware of that.


rayne February 24, 2013 at 08:25 am

the Australian rifle men are trained to tap the FA with every reload to ensure a round is properly chambered however a civilian who is not going into combat there’s no reason ore having it

also eugene stoner’s original design of the m-16 did not have the FA the mility added it because all the previous “battle rifle”s had it


Ryan Stubblefield March 2, 2011 at 11:03 am

I’d still agree with most people liking the look of an M4 profiled barrel. ESPECIALLY the armchair warrior or 511 types out there. It’s “tacticool”. I was trained to tap the FA after loading a mag in Basic while on the range at good old Fort Benning. As far as further training or combat ops as a member of the 75th Ranger Regt., I’ve never had use it since. The FA seems to be a throwback to the M16A1, developed during Vietnam after the original M16 had ammo problems, killing off whole platoons due to weapon malfunctions. The weapon could also jam from dirt, debris and excessive humidity. An FA was added to help and has been carried over into modern versions since then.


Dale October 9, 2016 at 01:45 am

My AR-15 is made by Colt and I’m pretty sure that most of the parts they use in their rifles are from the same “batches” (for lack of better word) that they send [sent] to the military. Therefore, it actually makes economical sense on their part to just throw in the same barrels they make for the military into their civilian models. I mean, why spend the money purchasing new machinery that wont make the barrel cut when they don’t need to?..

Other than that, I guess there is a market for people just wanting “mil-spec” stuff… Personally, I like the look of the barrel cut even on a 16″ barrel, cause yah know, the more edges there are, the more tacticool it is


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