I have an M&P 15 sport that I am wanting to put a magpul rail system on. The rail I want to install on the gun is longer than what's on there now. Is there a way I can install a new gas block in order to put the longer rail on? What kind of gas block do I need in order to make this work? Any help would be greatly appreciated!

Yes, you can install a different gas block and this is a common modification. You probably want a low-profile gas block to fit under the longer rail. Measure the diameter of the barrel at the location of the current gas block - it is probably 0.750". You need to match the measured diameter. The gas tube is held in the gas block by a pin that must be removed. The old gas block will be held in place with tapered pins - make sure you drive them out in the correct direction. The new gas block might be held with pins, a set screw or it might be a clamp-on type; the choice is yours. Any of these methods of retention should work.

Magpul rail? All Ive ever seen from them were 2-piece handguards. if you are trying to install a longer handguard, a low profile gasblock wont help you.

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Cliff

I agree, have never seen a rail system from Magpul....rails to attach to their handguard, yes, but a rail hand guard, no.

Also, I would use a dremel to shave down the existing front sight base instead of replacing it with a different gas block.

Yes I meant to say I am wanting to install a different handguard. Which will be longer than whats on there now. How would you suggest I put on the longer handguard if a low profile gas block will not do the trick?

A low profile gas block will do the trick. However, if you don't want to buy one of those you can cut down your existing A2 front sight to allow it to slip into the longer hand guard. Just do a Google search on free float hand guard installation and you'll see what we mean.

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Still carrying my S&W 642

Another option is to get a 2 piece free float carbine rail with cut out. Then you're not getting rid of a solid, pinned front sight. But as others mentioned, Magpul doesn't make a rail system. They make a hand guard replacement which needs a delta ring and retaining cap. You're not going to get one on there that's any longer than what you have. The mid length and rifle length are meant for longer gas tube systems.

I want to take the front site post off. I don't like the fixed front sight. So is there any way I can put the longer handguard on or not with the gas system that is on there? I have read on here and other places it's possible but than some say it's a not. Why wouldn't putting a low profile Gas block on work?

Yes, you can. Here is my Armalite, which came with a carbine-length handguard. I put the low-profile gas block and a Yankee Hill Machine Spectre-length free-float quadrail. They make mini, carbine, mid, spectre, and rifle-length quadrails. I did not change the gas system other than the gas block.