FTF problem with new 9mm AR

[Captain33036]

Hello

I have a new 9mm AR: Bushmaster lower and CMMG 9mm upper, 9mm buffer. The magwell block appears to be the cheap ProMag plastic one.

I get failures to feed about every 1 in 10 rounds (loading 10 in a mag). Not sure if it is a break in issue, mag related or magwell block related.

It came with a very cheap plastic ProMag magazine and in the first trip to the range, I had quite a number of failures. Mostly failure to feed. Even when cycling by hand.

The feed ramp also looked as though it was flat and banged with a hammer a couple of times. Weird.

SO: I took a stone to the feed ramp and rounded it out a bit. Since the failures seemed to be mag related, I ordered new Metalform ones (20 round).

I used those today...very tight...heck of a time getting rounds in (I will get a loader). This got better after some lube and working the mag. Whew.

Reliability was much improved, from the start, using these new mags. I loaded just 10 rounds at a time (thumbs hurt) and got one failure to feed in every mag. Same results, both mags.

I was wondering if anyone had any advice or input on this issue? I have only had a chance to get 200 rounds through the gun.

Will this go away as the gun breaks in?

Will this go away when the mags break in a bit more?

Should I stone the feed ramp more?

Should I consider replacing the magwell block? (this can be expensive...so I would rather avoid, if I can...but....the gun MUST run 100%...regardless of cost).

Any advice would be welcome.

Thanks

John

 

[JDGray]

Is the magblock adjustable on yours? My RRA magblock is, and it needs to be pushed up as high as possible, without binding the mag catch. I have also seen the front edge of the magazine, not always rest under the feed ramp lip and lock in nice and tight. I could alway tell on my RRA if this happened if the mag had some fore and aft play to it after seating it, if it moved, it was behind the lip not under it. My RRA came with an Uzi mag, and does not have a hold open follower, and because of this a full mag was kinda hard to seat with the bolt closed. I down loaded by a round or two, to help with seating the mag home.
Good luck!

 

[Captain33036]

Hello and thank you for the reply.

The magwell block is a top loading kind, you have to take off the bolt hold lever to put it in. It has some up and down play in it...maybe a mm or two. Not sure.

The improvement over the first situation was to stone the feed ramp to deepen it and round it out, along with the new Metalform mags.

It seems that most often it is the second to last round that jams. It seems to get misaligned and then impacts on the edge of the chamber on stripping and loading. So the bullet gets pushed back into the cartridge.

There are two copper streaks on the outer edges of the feed ramp.

And the rounds seem to get very tight in the mag.

SO, I am wondering if this will get better as the mags break in. And, I wonder if more stoning of the feed ramp would help?

I might try stoning the feed ramp edges a little bit more today.
Am going to order the Lula loader...that might help get the rounds fitted better in the mag.

Appreciate any advice.

Thanks

 

[wally]

Every one of the plastic ProMag I have for my RRA need removal of the "flash" and moulding marks to feed. They've been OK since, but I'd suggest seeing if you can find some of the old C-Products mags -- these have worked great although the early model black followers needed some work to lock back on the last shot, the red/orange ones were all good out of the box.

I'd also be suspect of the ProMag mag block, their stuff is in general not very good, I fail to understand how they stay in business while better suppliers go under.