I recently built a carbine for a friend and he is having some feeding problems.

Parts:

-RRA lower and parts kit (Bushmaster trigger group that was a taken from annother complete lower)
-RRA flattop upper w/ new RRA "enhanced" complete bolt/carrier group
-Wilson chromemoly 14.5" M-4 barrel w/ Cav-Comp (OAL 16")
-ACE entry-length skeleton stock (w/ carbine buffer and spring)

Ammo - Lake City M193, AE 55gr. FMJ, Swiss GP90, various reloads.

Mags - 13 different mags that all fit/funtion in other ARs - (BM 10's, ProMag 10's USGI 20's and 30's)

The problem is intermittent, but basically the bolt occasitonally misses the case rim on a round, dragging the round forward and jamming it into the feed ramps.

In a different post, Dano523 described this condition well:

the bolt is slipping over the top of the round (grabing the round after the rim), wedging the bullet tip into the barrel extension, and the bolt climbing over/past the rim and the bolt lugs denting the top of the case (bolt stuck on top of the case with the bullet tip in the barrel extension.

Any ideas?


Thanks, guys!

Tony

I think your mag must be sitting too low in the well.

You might try to tighten up the mag release.  (Push it out and rotate a time or 3 to have it hold the mag a little higher)

HTH

Good luck

TXL

Thanks fo the reply, but I tried that, to no avail.

Tony

Yes, it does.

Tony

Check the mag catch for proper adjustment.  The threaded part of the mag catch should be flush with the button.  If you can't get it flush, remove it and turn the button 180 degrees and reinstall it.

Could also be weak mag spring or a bad follower.  In a USGI 30 round mag use a green follower and a Wolff +10% spring and see if it goes away.  Don't use the BM 10 rounders nor the Promags.  Use only the USGI 20s and 30s while testing it. You can buy the Wolff +10% mag springs in 1, 3 and 10 packs.  I have a few orange (just like the green ones) followers if you need them (free of course).   Since this is a carbine I would also recommend a Wolff XP M4 extractor spring, and if he's going to run a regular CAR buffer a Wolff +10% action spring.   You can get the springs directly from Wolff www.gunsprings.com, from MidwayUSA www.midwayusa.com or Brownells www.brownells.com

Quoted: I recently built a carbine for a friend and he is having some feeding problems. Parts: -RRA lower and parts kit (Bushmaster trigger group that was a taken from annother complete lower) -RRA flattop upper w/ new RRA "enhanced" complete bolt/carrier group -Wilson chromemoly 14.5" M-4 barrel w/ Cav-Comp (OAL 16") -ACE entry-length skeleton stock (w/ carbine buffer and spring) Ammo - Lake City M193, AE 55gr. FMJ, Swiss GP90, various reloads. Mags - 13 different mags that all fit/funtion in other ARs - (BM 10's, ProMag 10's USGI 20's and 30's) The problem is intermittent, but basically the bolt occasitonally misses the case rim on a round, dragging the round forward and jamming it into the feed ramps. In a different post, Dano523 described this condition well: the bolt is slipping over the top of the round (grabing the round after the rim), wedging the bullet tip into the barrel extension, and the bolt climbing over/past the rim and the bolt lugs denting the top of the case (bolt stuck on top of the case with the bullet tip in the barrel extension. Any ideas? Thanks, guys! Tony

It is catching the side of the case.

The mag catch/release button are flush - I tried adjusting it tighter and loser, but it still does it.


Next time out I'll use only LC and USGI mags, but I tried the diff mags/ammo to try to pin the prob down to a specific ammo or mag  - and I don't think that's the problem - BTW - I am using green followers in the USGI mags.

Assuming for a second it's not a mag/ammo problem, what else could it be? Out of spec magwell or cut for the mag catch? out of spec mag catch?

Thanks for all the replies, guys!!


Tony

Quoted: Assuming for a second it's not a mag/ammo problem, what else could it be? Out of spec magwell or cut for the mag catch? out of spec mag catch?

Could be, try his complete lower on a known good complete upper and see how it runs.  

Quoted: Could be, try his complete lower on a known good complete upper and see how it runs.

Agreed -- or at least try another bolt/carrier.  I had a similar problem with one of my rifles awhile back, and I swapped parts with other rifles until I isolated it to the carrier.  It turned out to be a leaky carrier key.