M*CARBO Brotherhood

New M&P Mag Issue

Pretty excited about how well my S2K is functioning after getting it back and having the trigger kit installed.

Apologies in advance for not being able to find this if it’s been previously discussed.

Yesterday I made a quick trip to get two more mags and a bipod.

They didn’t have the P-rail mount magpul bipod that they spoke to me about over the phone and sold me a UTG RECON 360 for about have the price…

Got home and the new mag didn’t latch in. The latch hole in the new mag is only .005” smaller than the promag that came with my S2K. Otherwise appear very similar.


Should I change out this type of mag? (My son in law has a 40 m&p so I guess he could use these mags?)

Or stay with promag? I’m out of the loop on mags and could care less about the name, I just want a reliable functioning magazine

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My experiences with Promag are consistently bad. I have a few 10 rounders that haven’t failed yet, but I won’t trust them. My 32 rd M&P Promags have never run 3 times in a row - don’t trust them.

I’d say get the S&W mags to run. Have you tried tap’g them to seat them? Seriously … bop’m on the base pad and see if they don’t seat fine. I bet they do.

I bet they’ll seat on an open bolt with less bop’n too. I think you are experiencing a mag spring strong enough to trust.


Ha! Thank you so much!!!

As I was reading your post I was thinking no that’s not going to work. BUT dummy me didn’t try it with an open bolt. I was sure it wasn’t going to help cause previously I gave it a pretty good whack with my palm. So I got out the S2K and with an open bolt it latches effortlessly??? I try it like several times and perfect… close the bolt and give it a strong tap with the palm out my hand and no latching. OK, it’s time for a BFH so I whack it about as hard as I could with my palm to the point I feel like I’m not going to break something and all I got out of it is a sore hand…

I can live with this, it may fix itself after enough uses? I was so excited I forgot to open the second package and try it. Thank you!!!

I’m just happy to see it working because of living as far away from that store as I do, I didn’t want to return them.


I’ve had decent success with both my standard size and extended M&P.40 ProMags, but haven’t tested them extensively. Maybe 200 rounds through the extended, and the one malfunction was a bad jam.

I was hoping ETS would make .40 mags but seems like they’re just doing 9mm. And S&W doesn’t seem interested in extended mags, so I’m probably stuck at 15 rounds. All the more reason MCARBO needs an on gun mag storage solution…


Forget running to the store. Get them online and save some bucks. My preferred go to is gunmagwarehouse.com

Good prices, cheap shipping. Name brand and after market stuff too.


Check these out. Good price online https://www.sportsmansoutdoorsuperstore.com/products2.cfm/ID/206654/3008591/smith-and-wesson-mp40-m2.0-compact-40sw-13-round-factory-magazine. $15.99 @TheThreeLaws


Dred, I have no idea what has changed but all three (the original promag and both new S”&Ws).

I got the mail about an hour ago and to my surprise I had a package from MCarbo. So I installed a recoil pad, recoil buffer washer and swapped out the rear peep sight.

As I was walking away to let the loctite to cure I thought that I better check that other mag. Open the box and it went in and latched effortlessly? Checked to see and the bolt wa closed… Grabbed the other new one and it latched? No clue but am very pleased. Thanks again!

MCarbo parts and part installations are so awesome! High quality parts at a very fair price. And so simple to install, took me all of 1/2 hour for the rear sight, but pad and recoil buffer washer.


Thanks to the rest of you for the links, I will check them out and get a few more mags.

Last night I had to make a trip to my son’s house to get an engine stand and my chopsaw. He lives near Deguns so I just ran in to do some business with them. I don’t mind paying a little extra to keep a nice big store like them within an hour of me plus they have shooting ranges.



Those are the compacts, I’m afraid they won’t fit.


Well they sure look like the same thing as the promag that came with it…

But now it won’t feed out if any of the magazines. Back to the drawing board…

I was disappointed and walk away from it, took out my Steyr M40-A1 and took out my frustration on some steel targets. I was nailing the 12” at 50 yards but the 6” was like only 1 out 10 shots. It always makes me feel better making me look better than I actually am lol


Couldn’t sleep so I finally got up and decided to look at this issue again.

What I found out is that all three mags have a little bit of movement when installed.

So I installed the promag with three rounds kind of slamming it in there and noticed the first round is really sticking up (more than it was after I loaded it.

I let the bolt slam shut and it fed in. So then second round was sitting more normal and I knew from experience it was going to hit 1/2 a chamber low. So at this point I move the end of the magazine forward (bottom of magazine held with finger pressure forward to muzzle end). Let the bolt slam shut on its own and it went in (but not as nice as it should of).

I cocked it and doing the same procedure it fed the round into the chamber just like the second round.

Then I try the new m&p mag using the same procedure. I could not get a round to feed no matter what I did.

The new mags seem to have a stronger spring but the angle on the lips seem to hold the round a little lower than the promag.

Wish it was an easy answer and I did have the compact mags but I’m pretty sure I don’t. Searched the mfg part# and came up with full size mags.

Thinking I may have messed something up slamming the factory mags in to latch. Tomorrow I’ll remove the mag release and inspect.


with the play you have if you put pressure up on the magazine does it load?


No, pushing up doesn’t seem to help, only forward which changes the angle and points the round up into the chamber


I just tried it again and it’s hit and miss now with removing the tiny bit of play by pushing the magazine

This was my pride and joy with both accuracy and functionality until I started screwing with it


I think I found the problem


Feed ramp? Stuffed in the receiver somewhere or … on in the spare parts pile?

To be fair, my sub is cross town so I can’t pick it up to verify feed ramp location.


I just cleaned my entire reloading room thinking it has to there someplace but no luck. At first I thought maybe I knocked it out by slamming the new mags into it trying to get them to catch. But I don’t see any impact marks where the mags hit anything. Still not sure why they wouldn’t latch in and the promag would.



probably snapped out last round you fired, and ya didnt notice. why i went with the mcarbo stainless unit and buffed it.