Chambering problems...Hope somepne can help

[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.

1. Remove the magazine
2. Engage the mechanical safety if possible
3. Fully close the buttstock
4. Turn the carbine so that the magazine well faces you
5. Take a knee
6. Hold the forend of the carbine with your right hand
7. Hook your left thumb over the charging handle latch
8. Angle the carbine such that the buttstock is closer to you than the barrel (muzzle tilted slightly away from you)
9. 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