Hello everyone,
I'm highly interested in purchasing specifically the DDm4 picatinny quad rail 15inch for my S&W M&P. It has the A2 front site which I plan to remove and add a low profile gas block to. Just before I spend $395 on this rail, I just wanted to make sure it is compatible for my AR. From what I've researched it appears to be compatible but no one talks directly about this specific set up. Again I believe it is, as most but not all AR parts are universal for different brand AR's, but just wanted to throw this question out there to be sure.

My second question: the standard M&P comes with a 16inch barrel, my question is what length is the gas tube: carbine or midlength? I know it's one of the two, but I've read posts about both. I need to know this just incase I cannot remove the gas tube from the A2 site and need a new one for when I install this rail. Otherwise I plan to use the same gas tube and just add it to the low profile gas block.

Thank you so much for the reply. Yeah that first paragraph I had read on their site, it was more of a question of it fitting to the frame of the rifle. Essentially I know most AR's have universal uppers at the front end, but again just wanted to double check. And thank you for the advice about the fsb and for mentioning other vendors with better prices. I'll have to look for the rail elsewhere

Some M&Ps are midlength gas guns (Magpul edition, VTAC) but there won't be any problem with the upper accepting the DD rail system you're buying.

With the FSB, you're going to remove the bayonet lug and swivel if you elect to contour it down.  Otherwise, getting a 2" long gas block from Midwest Industries or a "race" block that covers both taper pin holes is my advice.

If your lower has Mapgul engraved on the ejection port side, you have a midlength gas barrel.  The box would say 811053 or 811054.  Otherwise it's most likely a carbine.

Truly appreciate it. Done deal and buying now

Just double checking on the gas blocks you were talking about. I found the MI micro gas block .750 and found the doublestar race gun gas block, those are the ones your talking about?

Ahhh I see now not the micro cause it's less than 2"

Yes!

Nitride 1:8 twist 5R barrels.  Also the M&P10s were originally offered with a midlength gas but their gas tubes were slightly longer than the AR-15 tube.

You're quite welcome, Sir.

Here's a little inspiration for you.

I built this off M&P Sport receivers a few years ago.







I use a KMR 13.5 and WOA stainless rifle gas barrel, CMC 3.5 flat bow trigger, and the VLTOR A5 system.  The WOA barrel was turned slightly lighter toward the muzzle to allow for a single OD forward of the gas block, and then bead blasted.