AR won't chamber

[cqcn88]

I have an oly arms ar that won't chamber a round off the mag. I had been using the lower for a different upper for ablittle while and I just put three oly upper and lower back together. I never had a problem before. When the bolt is locked open, insert mag, release the bolt, it picks up the round and rams it into the feed ramp where it is rather firmly jammed into the gap. It happened regardless of which side of the ramp is in play. I put the lower back on my bcm upper with bcm bcg and charging handle and had no problems. I put the oly back together and switched out the bcg to the one I know runs, same problem. Replaced the oly bcg and switched out the charging handle just to eliminate something else, same problem. So the lower and bcg run fine on a different upper. It looks like the tip of the round is just not sliding up the ramp, instead it's lodging in the gap. Oh yeah, I did all the above with 3 different mags and 2 different ammos, no change in the problem.

I know its another jammed ar thread but I'd appreciate any insight. Thanks.

 

[Double T]

Need a new buffer spring?

 

[cqcn88]

Need a new buffer spring?

I don't think so because when I put the lower on the functioning upper the buffer assembly didn't have any problems. When the bullet jams into the feed ramp it jams hard, scars up the bullet pretty bad.

 

[Vlad the Impaler]

Rifle barrel extension and M4 ramped upper reciever?

 

[mvician]

Turn your mag catch in one more turn and see if that helps.

 

[cqcn88]

Standard ramps. I'll try the mag catch when I get home. Thanks.

 

[cqcn88]

Mag catch is all the way in, same problem.

 

[THard6]

Mag catch is all the way in, same problem.

uhhh sell to Thard6 right away.

 

[Disposable Heart]

Let's see; when you say different magazines/ammo, what exactly are you using?

How old are your magazines? What kind are they? Decent feeling spring tension? I've had older mags do what you describe, even with M4 ramps due to poor feedlips (out of spec) or old weak springs.

What kind of ammo? My old Bushy 20" with standard feed ramps would not do softpoints of ANY persuasion, no matter what. Same with long seated or long projectile (read: heavy weight) JHPBT stuff.

Failing that, sell Oly to chump or Fudd for $2k... Sorry, couldn't resist...

 

[cqcn88]

Brand new pmags as well as a couple different older metal mags. Pmc 55 fmj and tullammo 55 or 62 grain, not sure which. All iterations produce exact same results. Just jams into the slot in the feed ramps. Both sides do the same thing, ramps do not appear damaged at all.

 

[Double T]

A silly question, but you aren't loading 30 rounders with 30 rounds are you? Often times they are too stuck in the mag for the bolt to strip the round

 

[MtnBiker6510]

Scratching my head with this one, & looking forward to whats found.

BTW: It sounds like you have narrowed it down pretty well & other than the barrel extension everything else has been eliminated, why don't you take the upper & lower apart and get a good pic of the barrel extension so some of the experts here can look to see if there is some problem the rest of us couldn't see or notice.

 

[cqcn88]

A silly question, but you aren't loading 30 rounders with 30 rounds are you? Often times they are too stuck in the mag for the bolt to strip the round

I initially had about 20 rounds in a 30 round mag but I took it down to only 2 rounds to eliminate that possibility. No change. I'm going to get a picture of the barrel extension.

 

[MtnBiker6510]

I initially had about 20 rounds in a 30 round mag but I took it down to only 2 rounds to eliminate that possibility. No change. I'm going to get a picture of the barrel extension.

I've loaded hundreds & hundreds of mags with 30 rounds and NEVER had an issue. Quality rifle + quality mags = non-issue. My rifles and my . Glad you tried this too, though. Good job narrowing this down OP.

Look forward to seeing the pic.

 

[cqcn88]

Barrel extension.

Also just swapped out buffer springs to one that is nearly new. About 100 rounds new.

 

[MtnBiker6510]

I see you have the Rifle Barrel Extension and not the extension made with the M4 feed ramps and the M4 ramps cut int he receiver.

If I am communicating this well, the M4 feed ramps were a solution to the problem of the carbine gas system causing jamming as the cartridge would still be rising when it is trying to be picked up resulting in the bullet being jammed against the chamber wall causing a malfunction. I usually dismiss this as I only think of it applying to full auto rifles, but it seems like your action may be cycling quickly and in combination with the lack of M4 feed ramps may be causing your issues.

Are you using this on a rifle length gas system or a carbine or mid length gas system?

If it is on a carbine length gas system do you have access to a heavy buffer? A heavy buffer might help by slowing the gas system enough for the cartridge to be lined up properly to the chamber.

 

[cqcn88]

It's a carbine gas system, but that's not the issue. It jams when I try to initially try to chamber a round. Pull the charging handle and let it go or lock it back then use the bolt release, it doesn't matter it always jams the round into the feed ramp. Not a while firing problem although I have to assume it would do the same thing while firing.

 

[MtnBiker6510]

I assume you have checked the upper for where the carrier rides. A disturbance there might slow up the carrier in its path.

I would try your lower receiver, magazine, bolt, CH & ammo on someone elses upper with rifle extension and see what happens. If it cycles consistently you've eliminated the items swapped and know it is the upper or extension. I'd give the ramps a polish with a dremel (polish, don't remove material) give it a good cleaning, lube and try again.

 

[j706]

Does your bolt go into battery with a empty chamber OK? Easily? Any chance of posting a pic of the rifle with loaded mag in place and upper installed looking through the ejection port?

 

[Vlad the Impaler]

ME TOO

Does your bolt go into battery with a empty chamber OK? Easily? Any chance of posting a pic of the rifle with loaded mag in place and upper installed looking through the ejection port?

I'm starting down this thought process too. Curious if the bolt carrier has a sloppy fit for some reason, or downward pressure due to a bent key or tube. However, the tube/key issue would be too late in the bolt closing stroke to cause the crash uppon stripping a round.

Empty and bolt chambers easily or drags? More drag on this carrier than another? Gas key or tube has dings or drag marks? Crap on the rails of the upper carrier or top of the receiver? How about the charging handle..OEM flat or bent down, putting downward pressure on gas key? Junk in the charging handle recess in the upper?

Can't wait to learn something here.......

Looks like you can see the crash marks below the ramps on the upper.

Is the upper to lower fit really tight? Tight in the pivot and loose in the take down?