Chambering problems...Hope somepne can help

[mlosi762]

Hey guys, took my first build to the range last week. Fired about 50 rounds of PMC 55gr .223, no problem. A buddy of mine came and brought some surplus m855 that he had. First round of that failed to chamber fully (bolt wouldn't go into battery, and FA did nothing to help), and we had to pry the BCG back with a piece of a cleaning rod (gouging up my ejection port in the process), to get the round out. Broke it down, inspected the chamber, cleaned it up, and tried again with a new round different pmag, same issue. This has happened now with several types of rounds not chambering. There's no obstructions lodged in there and I've tried everything I can think of, and nothing seems to work. Also, I'm well aware of the .223 vs 5.56 issues, but can’t even get a .223 to chamber now.

Barrel is a CMMG 1/7, 5.56 chambered, 16" carbine length.
BCG is Daniel Defense
BCM carbine length spring with H buffer.

Had an AR certified gunsmith check my installation work before I fired it (headspace/torque/etc), and he gave it a "go". Hope I can get some suggestions on what may be the problem before I have to spend $$$ on getting it checked out.

Could I have bought a crap barrel? Anyone else have issues with CMMG?

Thanks

[5pins]

The fact that you fired 50 rounds and did not have any problems until you tried some surplus ammo is too coincidental.
I would take a look at the barrel extension and make sure there is no obstruction.
Take a look at the bolt and make sure that the ejector and extractor are working properly. In fact just take the whole BGC apart and give it the once over.

[mlosi762]

The fact that you fired 50 rounds and did not have any problems until you tried some surplus ammo is too coincidental.
I would take a look at the barrel extension and make sure there is no obstruction.
Take a look at the bolt and make sure that the ejector and extractor are working properly. In fact just take the whole BGC apart and give it the once over.

That’s what I thought about the ammo too. But now nothing chambers at all. Already checked the barrel extension, nothing stuck in there, and cleaned the BCG real good when I first had problems. Pretty much gone over every user level PMCS procedure there is, and can't figure out the problem. I’ve had issued weapons get all kinds of crap stuck in the chamber and BCG while in the desert, but never seen malfunctions like this. It’s driving me nuts. I have a feeling I may have just got a shit barrel.

[Quib]

That’s a good troubleshooting problem you have on your hands.

It’s strange that up till the introduction of the M885, that the weapon functioned fine. How does the action feel with the weapon unloaded, just pulling back on and riding the charging handle slowly forward?

Can you feel a point along the bolt and carriers path, where you start to meet resistance?

[5pins]

If you have access to another AR I would try swopping BGC and see what happens.

Another thing you could try is to separate the upper from the lower pullout the BCG and try dropping a round in the chamber and see if it chambers.

[mlosi762]

That’s a good troubleshooting problem you have on your hands.

It’s strange that up till the introduction of the M885, that the weapon functioned fine. How does the action feel with the weapon unloaded, just pulling back on and riding the charging handle slowly forward?

Can you feel a point along the bolt and carriers path, where you start to meet resistance?

Going to play around a bit. Unloaded, then with some dummy rounds. Going to try using the BCG from my other upper to see if it chambers/cycles rounds. Hopefully I can narrow it down.

[mlosi762]

If you have access to another AR I would try swopping BGC and see what happens.

Another thing you could try is to separate the upper from the lower pullout the BCG and try dropping a round in the chamber and see if it chambers.

Lol. Just thought of that while repling to Quib. Thanks none the less though 5pins.

[mlosi762]

Going to screw around with this damn thing. If I can't figure it out, I'll take it completely apart and take some pics of the parts to see if anyone can spot something out of wack that I missed. Thanks guys.

[Quib]

Sounds good. Keep us updated.

[Optimus Prime]

I'd almost run a broken shell extractor through it just for the hell of it myself. I've seen a Ma Deuce with a busted case where the chamber looked fine, but sure enough, there was half a case lying under the gun, and it would not chamber a round. Just my 2 cents thrown into the mix.

[5pins]

I'd almost run a broken shell extractor through it just for the hell of it myself. I've seen a Ma Deuce with a busted case where the chamber looked fine, but sure enough, there was half a case lying under the gun, and it would not chamber a round. Just my 2 cents thrown into the mix.

I had the same thought.

[mlosi762]

So here's an update. Swapped out BCG's, same problem, so its not that. Has to be the chamber itself, right? So took the entire upper apart, and it looks like there may be a tiny bit of a case neck lodged in the chamber. Hard to see even with a surefire light pointed down in there. But will try and extract it (gotta go buy a shell extractor). If what I think I see isn't some brass, then I'm at a loss. Is it possible that this chamber just is't to spec? But if that's the case, I don't understand how I could run 50 rounds through it before having an issue. I have my 16" middy BCM BFH as my "main" upper, so I'm not having to go without, but will be pissed if I got to sink more money into my back up.

[5pins]

If it was out of spec I don’t see how you could have gotten 50 rounds off.

[mlosi762]

Likewise. Might just have to bite the bullet and take it to an armorer. But it's like changing the oil on my car, hate to pay someone else to do something I should be able to do myself. Hope it is just a piece of brass in there thats causing the problem. We'll see.

[rebelEMPIRE]

Sounds like that most likely is the case. If you can get your hand on a bore scope, it would help confirm things much more easily. Any possible debris must be jammed in there pretty tight, too. Good luck mate; I'm keeping an eye out on this thread.

-rebelEMPIRE

[Optimus Prime]

It's not a bad idea to pick up a broken shell extractor for anything you plan on shooting milsurp ammo through anyway, it's like a $5 insurance policy.

[Timberwolf]

Is the chamber .223 or 5.56?

Did you headspace with a .223 or 5.56 headspace guage?

[mlosi762]

It's a 5.56 chamber, and the barrel is stamped as such. I don't have a headspace guage, but had the headspace checked by a certified AR armorer at my local gun store. Didn't want to shoot a weapon without having someone who knows more about building guns than me verfiy my work. Still need to do more investigating, but school and work been keeping me pretty occupied lately. Few more of my own "tests" to run, then taking it back to the armorer to double check things.

[Blankwaffe]

Try soaking the chamber down in CLP and run a chamber brush through it.If there is part of a case neck in the throat of the chamber that may dislodge it.Ive also extracted seperated cases with a .40cal and .45cal bore brush in a pinch.
Just because the barrel is stamped,roll marked or otherwise 5.56 NATO does not mean the chamber is actually to spec or correct.Ive been down that road for years with a couple brands.
One little redneck test I have used for checking suspect chambers and ammo(dates back to my Armalite tight 223 chamber days)is to remove the upper from the lower,pull the BCG,and clean the chamber until its spotless and dry.Then point the muzzle towrds the floor and take a round of the suspect ammo and drop it into the chamber and give it a slght push with a finger.Point the muzzle upward and see if the round drops out.If the cartridge sticks knock it out from the muzzle with a cleaning rod.Then inspect the ogive of the bullet and see if there are any rifling marks visible on the bullets ogive.
If so the ammo is either out of spec or the chamber is not true 5.56 NATO spec and has a short leade.Which in my experience has been the case nine times out of ten.
I had this very issue with Armalite chambers back in the late 90's thru 2002.The rifles would chamber and fire .223 Rem commecial ammo without issue.With some import ammo such as Wolf that is loaded to the long side and complicated with a foward bullet ogive,or 5.56 NATO spec ammo such as Q3131A,and some heavier bullet designs with long ogives the rifle would either not chamber the cartridges as the bullets ogive was forced into the short chamber leade,or would show excessive pressure and blown primer pockets.

[mlosi762]

Thanks for the info. I'ts been a few days, and I haven't been able to get around to it, but I'll give your "redneck test" a try when I have a moment (wife/kid/work/school) has kept me busy lately. I really hope this CMMG barrel isn't out of spec. I know it's by no means high end, but it still wasn't the cheapest option. At least I have my BCM BFH upper to run in the meantime! But what good is a back-up, if it's a POS??? Cheers.

[rob_s]

Mortarting the gun when you had the stuck case might have saved your ejection port from getting gouged up.


Remove the magazine
Engage the mechanical safety if possible
Fully close the buttstock
Turn the carbine so that the magazine well faces you
Take a knee
Hold the forend of the carbine with your right hand
Hook your left thumb over the charging handle latch
Angle the carbine such that the buttstock is closer to you than the barrel (muzzle tilted slightly away from you)
Slam the buttstock on the ground at the receiver extension end (the "heel") while simultaneously pulling down on the charging handle with your left hand

[mlosi762]

Mortarting the gun when you had the stuck case might have saved your ejection port from getting gouged up.



Familiar with that technique Rob, tried it a few times, no dice. The cleaning rod was the last resort. I had never seen a round jammed in so bad.

[rob_s]

I had never seen a round jammed in so bad.
I have. 75 grain Wolf if run for more than 200 rounds relatively quickly. I can shoot a thousand rounds of it between cleaning in short bursts like a match but if I try to use it hard like in a training class a case will stick around round 200 or so, and then I'll get a stuck case ever 50-100 rounds until I completely clean out the chamber.

This is over multiple rifles, all known 5.56 chambers (checked with Ned's gauge), etc.

[federalist22]

Just my 2 cents, but sometimes it's not the gun, it's the ammo. Was your M855 actually XM855? Not sure if this was a joke or not, but in a rifle course I took, if I recall correctly, it was mentioned that the X in XM855 (likewise for other x-variant nomenclatures of military calibers like XM193 (out of spec M193) is used to denote ammo that was supposed to be made to milspec, but failed the inspections process--therefore the lot was labeled with the X and sold off as surplus and probably cheaper than its non-X variant.

Now something which might keep the BCG from going into battery and properly chambering a round is that the round is actually exceeding the acceptable OAL (overall length), meaning the projectile was not stuffed into the casing far enough and the bullet is too long and out of spec--try other ammo with the same mags and see what happens or measure the 55FMJ stuff in millimeters or something against the M855 (or XM855).

I have seen this occur in custom-made M40A5 rifles, Mil-spec 5R Rem700s, and other match-grade platforms. On the bolt action rifles, the bolt will not close on some .308 handloads--human error in the loading process causing the OAL to be too long to chamber.

The chambers and barrels of some .223/5.56 better made MFRs can be very precise and out of spec ammo could be the culprit. Aside from OAL, the powder loads could be hot and that is the reason for the X and rejection by the MIL/LE inspections, which may also affect OAL if the bullet is sitting on the powder--OAL is too long. I could be wrong, but ammo problems are worth looking at.

[rob_s]

Just my 2 cents, but sometimes it's not the gun, it's the ammo. Was your M855 actually XM855? Not sure if this was a joke or not, but in a rifle course I took, if I recall correctly, it was mentioned that the X in XM855 (likewise for other x-variant nomenclatures of military calibers like XM193 (out of spec M193) is used to denote ammo that was supposed to be made to milspec, but failed the inspections process--therefore the lot was labeled with the X and sold off as surplus and probably cheaper than its non-X variant.

Now something which might keep the BCG from going into battery and properly chambering a round is that the round is actually exceeding the acceptable OAL (overall length), meaning the projectile was not stuffed into the casing far enough and the bullet is too long and out of spec--try other ammo with the same mags and see what happens or measure the 55FMJ stuff in millimeters or something against the M855 (or XM855).

I have seen this occur in custom-made M40A5 rifles, Mil-spec 5R Rem700s, and other match-grade platforms. On the bolt action rifles, the bolt will not close on some .308 handloads--human error in the loading process causing the OAL to be too long to chamber.

The chambers and barrels of some .223/5.56 better made MFRs can be very precise and out of spec ammo could be the culprit. Aside from OAL, the powder loads could be hot and that is the reason for the X and rejection by the MIL/LE inspections, which may also affect OAL if the bullet is sitting on the powder--OAL is too long. I could be wrong, but ammo problems are worth looking at.

http://www.federalpremium.com/resources/xm193.aspx

[federalist22]

I used this as a reference.

http://www.thegunzone.com/556xm.html