Problem with new upper.

[MudBug]

I built a new upper for my main carbine to replace the well worn old one and it's having problems.

• CMT upper
• LMT Bolt and carrier
• CMMG 14.5" barrel + YHM QD can mount (Perm)
• Samson MRFS-CXF
• Mega Lower, DPMS LPK (My old lower which always worked with my old upper)
• I've tried both the DPMS Heavy buffer and a standard "H" buffer

The problem is that the bolt keeps over-riding the bullets. It will seldom charge if I release the BHO, it misses the rim of the bullet and hits the bullet a bit higher up the case and locks up. It will charge more often if I pulled back the CH, but still I often have the same problem in the middle of a mag after firing a few rounds.

This has also put a few dings in the feeding lips of some of my mags.

Any ideas?

[deadwood83]

Maybe your bolt is overly loose? They should have very very minimal wiggle.

[M4arc]

If you put just one round in it and fire it does the bolt lock back?

[jmart]

Have you tried different mags?

[Robb Jensen]

Sounds like bad mags or improperly adjusted mag catch.

[Stickman]

How many different mags have you used, and is it mag specific?

[MudBug]

I haven't tried the standard "Short Stroking" test since it does always locks back when a mag is empty.

A few days ago I tried shooting through about 30 different mags and I separated out 2 (Bravo Co mags) that actually had dents in the feed lips which forced the bullets to nose bump the front of the mag, they couldn't "Lift" out of the mag body. I see this as a separate problem, but since I have never seen the dents in any of my mags before I'm wondering if it's something the upper did.

My mags are a mix of Center, Okay, CProducts, and lots of the D&H mags Bravo C0 sells.

I guess I really need to number all my mags and go test them all.

I wish I would have taken pics to show what it's actually doing since this was a new thing to me, my previous upper ran all of these mags without any trouble. The bolt is hitting about 3/4" forward of the rim and pushes the bolt part of the way out then locks up. Once it pushed it nose high into the top of the barrel extension, forcing the bullet back almost all the way into the case.

I'm not blaming this upper, or saying that any of the parts are the problem, I'm just saying that this upper is new and now I have this problem.

I'm not sure what is meant by "Maybe your bolt is overly loose? They should have very very minimal wiggle."


Thanks

[MudBug]

Sounds like bad mags or improperly adjusted mag catch.

Do these wear out? I have about 15k through this lower.

[Patrick Aherne]

Do these wear out? I have about 15k through this lower.

Yes, they wear out. If you're the same Mudbug that takes Tactical Response classes and posts at GOTX, I bet you've done a ton of tac loads and should get a new mag catch.

[deadwood83]

I'm not sure what is meant by "Maybe your bolt is overly loose? They should have very very minimal wiggle."


Thanks

I was just thinking that maybe the bolt was shooting forward before the BHO was all the way down. Kinda like 'riding' the BHO before it gets returned all the way to the original position.

And if it's the mags, try some Bushmaster mags. The ones I bought seem to let the case stick up more than the other brands of mags I have.

But forst look into what gotm4 and Stickman are saying. They are very knowledgeable.