AR-15: Handguards and Barrels

Recently a friend asked me a few questions about an AR-15 he was considering for purchase. It prompted a lengthy response on my part that I thought would be good to share here. The rifle in question was a Smith & Wesson M&P15PS, which is a piston carbine with traditional carbine-length handguards. Here is a summary of his questions:

Do you know if it’s possible to put a longer handguard on a carbine setup?  The handguard always look so short which seems to be bad for retention and also for possibly burning your self or resting it on something…  I would like to put a longer handguard on the M&P piston one, but would then need to put a rail mount sight further down the barrel do you know about people doing stuff like that?

As you can imagine, I had a few things to say about this setup:

I don’t know much about that particular model but on paper it looks like a decent, relatively basic rifle. I don’t see a forward sling mount and the barrel is the “M4 contour” which I would avoid personally given the relative thinness of the barrel at several points along the barrel. Sure, it probably won’t matter under light use but a medium or heavy barrel will last longer and dissipate heat better, especially under rapid or extended fire.

You asked about the handguard. The standard carbine-length hand guard is 7-8″. Mid-length is usually 9-10″ and rifle length is 12″. Given that this rifle has a piston system you might be limited in what you can do. Specifically, you mentioned concerns for having the hot components touching stuff. I’m not really sure this is something to be concerned about. I can’t imagine ever reaching my hand that far forward while carrying or shooting the gun although I do like the 10″ rail on my SR-556, which covers most of the gas block. Perhaps with your reach it could be an issue but that setup is standard issue for M4 military users (82nd Airborne, Rangers, etc.). You might touch something with the barrel or gas block, but that’s possible with any AR-15.

So, with the gas block you have, there may be no way to put a free-float tube on that rifle without it being some sort of over-size (large diameter) tube. You can of course replace those handguards with anything else that will fit a carbine setup but that will by definition not go beyond the front handguard ring, i.e., not achieve your stated goal.

My preference is and has always been to have a free-floating handguard with an integrated rail system (quad rail). This is because you can attach a sling, bipod or whatever you want and not have it create any stress on the barrel. If you press hard into a sling that is attached to the barrel, you can significantly change the geometry such that your shot goes way left (or right in your case). Same goes for bipod: it can make the POI go high if attached directly to the barrel as is the case with rail systems that simply replace the stock handguards.

The rifle in question looks quite good as a general purpose carbine. Put an optic on the top rail and you are all set. However, you don’t have any mounting points for lights, FVG, bipod, etc. and if you created a sling mount on the hand guard, that would stress the barrel as mentioned.

If this is to be a patrol carbine you have to ask yourself which features are really important. Would you even use a sling? Probably only in a SWAT/HRT role I would think. Same goes for FVG, bipod and perhaps even for a tactical light although I certainly keep one on my AR at all times. Bad things don’t always happen in the daylight.

Lastly, you mentioned the need to place a front sight further down the barrel if you covered or otherwise compromised the existing front rail, right? Be aware that this would only be ideal if the sight is rigidly attached to either the barrel or a free-floating handguard. In other words, if you cover that existing gas block with some sort of after-market extensions, they may not be rigid enough (mounted in the handguard rings) to keep zero with the new front sight. The plastic handguards don’t usually have to be held very tightly in place.

So, I would say that it is probably hard to go wrong buying any M&P product but depending on your intended purpose this particular model might be too much of a compromise. Then again, it might be perfect as a light, simple, accurate piston gun. Only you can determine that.

Well, you knew you would get an earful, didn’t you? 😉 Darn it, I need to get back to my blog!

And so I have.

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