I just purchased my first AR, the M&P15 Sport II, and I have a question about the hand guard.

Is it ok to mount a section of picattiny rail to the bottom holes in the stock hand guard, or will that interfere with the gas/or break the stock hand guard?

I will most likely use that section of rail to put on a vertical grip or one of the angled grips I have been seeing.

I was told by the guy at the gun shop that those holes are for the gas to release, and that covering them up could damage it.

Any help would be appreciated. Thanks!

1. You should be fine.

2. The gas system runs on top of the rifle from the A2 front sight post, through a gas tube, into the upper receiver.

3. Either the guy at the gun shop is an idiot or you might have misunderstood. The holes at the bottom and top of the handguard are to vent heat away through convection.

Lastly, congrats and welcome aboard.

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-John

Is it going to be too much heat to have a section of rail covering some of the holes on the bottom of the hand guard? Also, is the stock hand guard stable enough to hold a vertical grip while shooting?

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S&W M&P 15 Sport II

No. Your barrel can handle more heat than your handguards. Bare hands will fail from the heat radiating through the handguard than either the handguard or the barrel.


Keep in mind that the stock handguard on the M&P 15-Sport does not have heat shields. It is the single reason some people (like me) replace the stock handguard. Because I know the next question, below is how you replace a stock two piece carbine length handguard.

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-John

Dump the handguard and get a Magpul replacement and you can mount what you want.

MOE SL™ Hand Guard, Carbine-Length – AR15/M4

The heat should not be a problem (most of it should be up top with the gas tube) and the stock hand guard while not perfect, should be stable enough. I have Midwest Industries drop in quad rails on my Smith & Wesson MP15's and they do fine with vertical grips. As long as the rail is solid to the stock hand guard you should be good to go.

There are a couple of manufacturers out there that make specialized pieces of rail which allow for the angle/taper of the stock hand guard.

I guess what I am trying to ask is if the holes in the stock hand guard are there to attach rails to, or just to let heat out?

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S&W M&P 15 Sport II

People have been attaching rails to those type of holes for a long time. I have a vertical handgrip attached to the rail that I put on the bottom of my Sport. No problems.

I read something like this and I have an immediate urge to run to the nearest wall and start knocking my head against it. Because sometimes things people say are so ignorant you just have to do something to vent.

If you have the Dust Shield open on your rifle you will see two small holes in the scallop cut in the side of the Bolt Carrier and those two holes are where most of the gases diverted from the barrel are released. Another small bit of gas is released when the gas key clears the gas tube in the receiver as the bolt carrier is driven to the rear. Finally just a really tiny smidgen of gas may get puffed into the receiver as the case clears the chamber. Quite simply there are no gases released from the barrel into the handguard unless the gas block was improperly installed rather severely or the gas tube has split due to a manufacturing flaw (only theoretically possible and I have never heard of this actually happening).

Now, in regards to your question. I haven't ever taken a close look at the handguard on the Shield but if you have a couple of holes in the bottom of your handguard and have a section of rail that fits the contour I see no problem with mounting that rail. However doing so will mean removing the handguard which can be a bit of a challenge on some rifles. If you are goint to that much work you may want to look into a handguard that has a rail machined into it so you won't have any screws to shoot loose or get a handguard that is equipped with keyholes that allow mounting rails/hardware without removing the handguard. Doing things like this are why the AR platform is so popular, we can customize our rifles to fit exactly the way we want them to fit us.

PS; I'm an old fashioned rifle shooter and have never understood the appeal of a forward vertical grip. Lights I get, bipods I get, vertical grips I just don't get and I think they just have to be uncomfortable to shoot with. I have a hunch that after you have that vertical grip mounted you'll find it's not nearly as useful as you thought it would be.

If there was any real world advantage to vertical or angular front grips on the AR platform, all of the top level competitors would use them. They don't.

They are there for air circulation. Heat rises out the top and cool air comes in from the bottom. Most people don't shoot enough for blocking a couple of them to be a problem. While mounting a rail on the stock hand guard isn't the best solution, it works well enough and people have proven it usually doesn't cause any issues,

One of the reasons a lot of competitors don't use them is because of the amount that they shoot. They have a huge amount of built in muscle memory. Their off hand goes to the same place every time they shoot. It stays there and their purchase on the weapon is better than the avg joe.

The novice shooter or even seasoned shooter does not always have that same memory. I can personally shoot with and without them but many people like myself like them because they are a grip point which helps us develop muscle memory. I also think they were more popular when quad rail, cheese grater, rails were the norm. Todays keymods, FF tubes & M-loks are much easier on the hands.

They were probably designed/intended more for heat dissipation/air flow as SgtSandman stated, but as we have said, people have adapted them for fastening small pieces of rail for many years without any ill affects.

It certainly wouldn't be any worse than some of the cheaper long aluminum free float tubes without any vent holes in them at all.