CMMG 10 round mag extension - FTFeed

[wheelguy]

I have been using 6 OEM mags for about a month now, 4 of which have the 10 round mag extention from CMMG. I noticed that every time I have a failure to feed, there is the following repeated behavior...
* only happens with the 30 round mags, never the 20s
* always the round trying to feed from the left side, never the right
* always on round #2 or #4 (not sure which)
* tip of round makes it just inside the chamber
* slide can not be pushed forward to complete chambering

Has anybody else experienced this? Since it always happens with a nearly topped up mag, I am assuming that the floor plate is catching on the edge of where the old mag bottom and the extension top meet, so I'm thinking about sanding those edges a little. That's just a guess, though.

Suggestions?

[jhs27275]

Since it always happens with a nearly topped up mag, I am assuming that the floor plate is catching on the edge of where the old mag bottom and the extension top meet, so I'm thinking about sanding those edges a little. That's just a guess, though.

That is a great guess.

Take the spring out and you should be able to feel inside the mag body and locate any over hang areas. Sand it down till it matches and you'll be good to go.

[wheelguy]

I tried feeling for some sort of ledge or lip that the follower might hang against as you suggested. Didn't find any edges, although the gap is easy to detect. May go a different route instead of trying to fix this one. Designing the follower so that its sharp edge passes by that gap is not a good thing.

[jhs27275]

It does not have to be much of an edge or lip for the follower or spring to get caught on it. If you can feel it with your finger nail it needs to go.

[wheelguy]

Thanks for the tip - that helped me to understand how to do it. I was trying to feel up inside the mag, but with my big fingers and no nails wasn't having any luck. I'll try taking the mag apart so that I can run my nail across the edge directly.

[jhs27275]

Use a flashlight and you can see where it does not match up inside.

[Chitty Chitty Bang Bang]

I have to agree and have noticed the same tendency....only on the 30 round mag extension from CMMG. Nothing bad towards CMMG as I have only had good experiences with them. I have inspected it, cleaned it (it was clean), cursed it, etc. Glad to hear I am not the only one with this observation.

[wheelguy]

Mine has been fixed and tested. I removed the CMMG extension and used a dremmel to put a small 45 degree chamfer on the inner edges where they meet and on the outer edge of the follower. Followed by smoothing the chamfer with fine sandpaper and wiping clean. No more FTF !

[MP_OHIO]

I have not had any problems with either of my CMMG 10round extensions. Might be a MFG problem with a certain batch.

[Valorius]

The factory mag body holds 27 rounds of ammo, so as long as you load 27 rds or less in the CMMG extension equipped mags, they won't have any problems at all with FTF's caused by the follower hanging up on the seam of the CMMG extension/mag tube.