Home CMMG Bench Report: AR-15 Chambering Issue, How Do I Fix This?

Bench Report: AR-15 Chambering Issue, How Do I Fix This?

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Just a quick overview of an issue I’m having with the AR-15’s 5.56 upper. I could use some input on if you think rounding off the back of the lock lugs’ square channel will resolve the issue.

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49 COMMENTS

  1. Have the same thing with mine and i was going to use a Dremel to round the corners of those three teeth starting with the center one first and then seeing if it's still marring then move to the outer two!

  2. Do you know if the scoring happen going in or when ejecting?
    It may happen going out when the spring loaded ejector is pushing the cartridge to the right.

  3. I had the same thought/issue with the bullets getting scarred. A lot of comments to sort thru, what was the consensus? OK to file, or need to be square?

  4. That is not a squib load. Squib is totally different. Also, the scratch on the bullet from the locking lugs is normal, and isn’t a problem. It’s happening during ejection, not when clambering, and when you fire a cartridge it doesn’t happen because the bullet exits via the barrel. Only when you eject an un-fired round will that happen. When you eject an un-spent cartridge, as the cartridge is being tilted out to the right by a combination of the ejector and extractor, it’s tilting and the bullet scrapes the lugs. When you fire it, the spent casing tilting out doesn’t have a bullet so it doesn’t happen. I would not modify the locking lugs over something this insignificant. I think you’d be more likely to cause an actual issue than you are to solve this non-issue.

  5. it's funny that you call it an AR. and don't say a brand. your lucky it's not for service. I hope you have a real brand as a home defense weapon. and if this is just a toy. well hope it don't blow up on you. 90% of the time this is what Frankenstein builds do. Milspec sir.

  6. well I'd like to say it's funny that you call it an AR. and not mention the brand. with that being said I work at a local gun range in Nevada and our customers put all guns through serious torcher test and I have seen and fixed issues. but most of our name brands don't malfunction. but I do see builds and low end rifles do this. not all are lemons but not every one is lucky. I don't make a lot of money. $25 commission on guns sold and $12 an hr wage. I did my home work and spent $1000 on my LE6920 and never had an issue. my advice is don't buy batch tested fire arms. you should not have to spend 500 to 800 and then need to make a change to make it work. out but back program pays $100 on long guns and $50 for Guns. it's unfair to you as a consumer. good luck to you and all gun enthusiast.

  7. Seen this several times if you sand and grind on the barrel enough some people get them to work but if you look carefully at the face of that round he has in his hand the bolt carrier extractor has scored the heck out of it. It’s not even round anymore. Every single one I have seen it is the bolt. I have put my bolt in several guns that is doing the exact same thing and no problems. The bolt is what is doing the feeding.

  8. Hey bro that is normal that a dimple forms on the primer.Also on metal mag on the front of mag where the mag sheet metal is folded and where the bullet slide through before the bullet goes into the chamber there is a bur or deformation on the mag causing the bullet to get sliced.

  9. What did you do you correct that issue? Was someone able to answer your question of what to do? I am currently having the same problem. When just using the charging handle for the rifle every so often the bad of the lug face gets caught and scrapping un the rounds, leaving lil shavings.

  10. I have a very similar issue on my Spikes Tactical system w/Adams Arms piston kit. The rounds on mine do not end up as potential slam fire, but do have the scoring on the round it self and the neck of the casing as you showed here. I didn't notice skiping o mine though.. Maybe I have a different problem because I've noticed double feeds on mine as well..

  11. Looks as if you have a small crack on the left side of the left feed ramp, if it's not I believe you can correct most of the problem with a small file and 3m wet or dry sand paper, also a dremel tool will work.

  12. The marks on the bullet look like rifling marks  ….like the bullet is hitting the rifling… I maybe wrong ..I reload  and you want the bullet  to hit the rifling… some people like to have the bullet jump to the rifling… if you made the bullets seat them deeper in the brass and  check the OAL ..I find by seating my bullets to hit the rifling in some of my rifles (bolt action) it makes them more accurate .. I see that your ar is not free floated that will help accuracy … I hope this helps

  13. Happens to me same thing it's not on extraction it's on chambering. Every other shell would have it on my because my left feed ramp had a burr waiting to hear back from POF dont want to mess up warranty

  14. I had the same problem when I installed a new barrel on my ar. Same gouges, but was bad enough to cause FTF. I rounded those slightly with a jewelers file, used 600 grit sand paper on the edges and feed ramps, and polished with a dreamer. Problem disappeared. Poor attention to detail from what was supposed to be a high quality barrel maker.

  15. That is correct, the dimple on the primer is normal from the inertia from the bolt loading a round, the other problem I would try a dremmel polish job first before picking up the files.

  16. I would simply replace the barrel extension….  Or fit a new "barrel and extension".  I might opt for  a Wilson  223 Wylde chambered match grade 1:8 twist barrel   "with extension" and be done with having that problem.  In Canada I would try to get a Colt Canada or Diemaco barrel with extension.

  17. that's not a squib round lol. A squib is when the round doesn't fully ignite the propellant, or the round was improperly loaded with the correct amount of propellant.

    What you have is called a "light primer strike" not a squib round. A squib will be noticeable by "BANG BANG BANG pop" a very faint poof or pop vs a full power bang. Never fire after hearing that pop either or you will most likely bulge your barrel or have a catastrophic failure.

  18. I am having the same exact issue with my new upper, the rounds look exactly the same and have copper jacketing left on the lugs in the same place as yours. rifle jammed on my first charge with Winchester 556 ammo and would not even chamber a round, jammed every time with Hornady SST 223. if I have my bolt held back and seat the mag release the bolt it'll chamber a 556 round but still jams very tight with the sst .223.

  19. Shoot the piss out of it to smooth the chamber and all my ar15's have done that primer mark. Everyone I've owned and seen has done that. It used to worry me too but I've never seen one fire because of it

  20. im having a problem with the casing being scraped in the magazine deep cuts from the BCG and its just enough pressure so the bolt wont close idk what to do after ten rounds of shooting it forcing the bolt forward i have a lot of case material on the bolt and in the chamber on the other hand im getting good groups at the long end i have zero problems with loading it without the mag in but that kinda defeats the point of having a semi auto

  21. Lubricant is the answer for most problems. I had a lot of problems today with my shell casing not ejecting and not pushing another bullet into the chamber…. I lubed it up real good.. It gradually got better with each shot. Finally I was rattling the shots off.. Felt great.. Today was the first day I shot my AR… It need oil bad and I had a lot of problems till I got it oiled properly.. Don't worry about overdoing it.

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