Hi guys, I've had my M&P 15or for 2 years now, and wanted to replace my current quad rail with a free floating rail. I need to know what length rail I would need and would the gas block be removed? Any suggestions on a brand would be appreciated. Midwest industries and Yankee hill seem to be very reasonable. Thanks again for the help.

Rail length is simply a matter of personal preference. Anything longer than carbine-length will need a low-profile gas block. I have a Yankee Hill free-float quad-rail on my AR and I'm very happy with it. I went with the "spectre length".

I went with a MI T-Series free float quad rail (carbine length). I like the carbine length for the simple reason I wanted to keep it light and simple. In the near future I have no intentions of adding anything to the rails to it make the rifle heavier than it needs to be. Just keep it a clean looking Sport.

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NRA member since 1974

Ok, that is definitely good to know, because I really didn't want to remove the gas block. I'm looking to do as little work as necessary to get the rifle felling tighter. Thank you both for the input, it was exactly what I needed to hear.

You will most likely need to remove the gas block. If you have to change the barrel nut, the gas block has to come off. You may need a low profile gas block.

It not hard to do so, don't sweat it. We can help if you have trouble.

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Freedom isn't free.

As stated above, if you want to install a free-float rail, you need to remove the gas block. If you can work a punch and a hammer, you can do this. Also, you may need to remove your flash hider/brake if you have one. You'll also need a barrel nut wrench and (preferably) a torque wrench to complete the job. I also wouldn't tackle this install unless you buy/borrow a receiver block and barrel vice (if you have aforementioned FH.)

Staying with a carbine-length rail is the easiest, but I've always been a sucker for a low-profile gas block and the Midwest Industries rifle-length free-float tube. It's an awesome, awesome look when it's all done.

Yep, what Rastoff said. There are a ton free floats out there, some require the use of a proprietary barrel nut, some don't. I went with the "old" technology Troy Battle rail, as it uses the factory barrel nut. The addition of the YHM clamp style lo profile gas block made it easy. The end result was very much to my liking.



Good Luck and good shooting.

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SFC, US Army, Retired

Also went with a Troy Alpha, 13" with Troy LowPro pinned gas block. Process is *supposed* to be relatively strait forward, other than S&W being opposite in pin direction.

I had issues driving the pin (it can be stubborn) out so just dropped it off at my LGS as they were doing a few things for me. They actually cut the block off despite my ensuring them the pin is removed in the opposite direction from everyone else, which I wasn't super pleased about as now I no longer have the option of going back to stock unless I can find an OR gas block somewhere. But, I don't really ever expect to go back to non FF so I guess it's not that big a deal. Anyway they said they've never been able to get a OR block off without cutting, but plenty of posts and videos show the opposite.

There was also a thread here (which I can't find now) mentioning they were not able to reuse the gas tube due to the way S&W pins it, but I didn't run into any issues, so that may have been an older design, or a one-off issue. But something to keep in mind.




https://www.youtube.com/watch?v=-gv1A9lh0MI

Plus a few links...

M&P15 front sight pins backward from most!

Follow the link in Post #1
If you hate your high profile M&P Optics Ready gas block.....

M&P OR model, what have you done?