Magpul P-MAGS and S&W M&P15 Tacticals

AR/M4 AR Technical Discussion
1

I figured out why the Magpul P-MAGs don’t lock up in the S&W Tacticals. It’s that the bottom edge of the magwell of the lower receiver is both longer and the Tactical isn’t beveled as well as compared to other lowers.

Here’s some random measurements from new rifles we have in the shop on the wall. The measurement is from the bottom of the carrier (bolt closed) to the bottom edge of the front edge on the magwell on various rifles.

S&W M&P15 T: 2.415" front edge barely beveled

S&W M&P15 A3: 2.3775" beveled well
Armalite: 2.362" beveled well
Bushmaster: 2.3935" beveled well
Colt 6721: 2.369" beveled well
Colt 6520: 2.3815" beveled well
Colt 6920: 2.368" beveled well

2

You don’t say? And didn’t we just have some guy here saying that it had to be the mags fault and there was no way it was his rifle? :rolleyes:

3

I’m trying to picture this and I don’t understand why this dimension is important. I would have thought it would be the bottom of the carrier to the mag catch since that’s where the mag is held captive. I would have also thought that the length of the magwell isn’t nearly as critical. Am I looking at this wrong?

4

The bottom half of the P-MAGs are wider front to back than the top half that actually goes up into the lower receiver. If the lower is beveled and isn’t too long it’ll lock up just fine. On the S&W M&P15T thats were the mag stops and doesn’t lock into the lower.

5

That makes sense. Now I can picture it.

6

S&W is aware of this issue.

C4

7

Are S&W lower made in house by S&W? Or are they contracted from someone else?

8

Based on what I’ve read elsewhere on the net, it would appear that some 15Ts allow for the mag to lockup and others don’t. Everyone that’s spent 10 minutes looking at the situation seems to have concluded that some of the 15Ts wells are toward one end of the spec where the bevel is, giving them a little tighter fit because of the ribs on these new magazines. It appears that the easiest fix is just to sand a little plastic off of the mag’s rib that contacts the bottom of the magwell and prevents the mag from inserting enough or at the proper angle to lock up. I’ve seen pics that some guy posted of the little bit of sanding he did to the mag’s one rib to solve the problem. To be frank, I don’t quite understand why people who own 15Ts and buy these mags don’t simply make this slight modification to that one rib and be done with it.

(C4IGrant, on a related note, a week ago I dropped you an email at your sales address and another through M4 but haven’t heard back from you. No interest in taking my money?)

Thanks, Mark

9

My M&PT takes the Pmags. On the newer tacticals did Smith stop using the CMT lowers? Mine came with a CMT BCG but I had them replace it with a LMT.

10

Contracted out.

C4

11

Hmm, don’t know that I got it. Send me a PM through M4C.

C4

12

Don’t know where they get their lowers for sure. 15A’s and 15T’s come with LMT BCG’s. 15 will also be changed soon I think.

C4

13

PM sent. Thanks.