Jamming up

My AR-10 which was recently assembled and is jamming up. It is slamming the bullet and putting a very large bent in one side of the casing, almost piercing a hole in the side. I have cleaned it tried oiling it ( helped for a few rounds. Pulling it back and letting it load it is jamming the bullet in so hard that i have to smake the butt on the ground while pulling back to get it to eject. Does anyone know what and why?

what caliber?
PMAGs or something else?
what brand of upper receiver? does it have feed ramps that correctly mate with the barrel extension feed ramps?

what brand of lower? is it a quality brand or an 80%? maybe the mag is sitting too low?

what brand of barrel? some barrels have better barrel extensions than others.

do you have the right combination of buffer, buffer spring, buffer tube? very very common mistake.

is it gassed correctly? over gassed? adjustable gas block? last round bolt hold open?

bolt over-riding the cartridge can be a symptom of over-gassing, and also under-gassed.

if you have too strong of a buffer spring, bolt might not be coming back far enough to engage the back of the cartridge. or if it's undergassed.

if you have too much gas, or too weak of a buffer spring, bolt rebound might be too fast before piece-of-crap el-cheapo mag presents cartridge to be picked up.

if your mag is crap, it might not be presenting and releasing the cartridge correctly.

some barrel mfrs are better at right-sizing the gas port, than others.

if the barrel extension is one-size-fits-all, the barrel feed ramps might not work with your cartridge. some mfrs use a generic 308 barrel extension which may be marginal for 6.5CM.

barrel feed cone might be inadequate.

if you have an adj gas block, get to last-round-bolt-hold-open as a first step.

Tell us about your ammunition. Reloads? How did you resize?(procedure)

Sounds like a zero head space issue possibly. The ar10 is a little tricky to get right . They are not standard like a ar15 . There are a few different platforms and parts don't always fit . I had this issue on my ar15 . It's got a Kreiger barrel and they tell you it might not work with a nickel boron bolt . I had the gun assembled by a smith and it was supposed to have head space checked. I got it home and ran a function check and locked the gun up . It didn't have enough head space . After a few choice words with the smith he was supposed to correct the issue . The head space was fixed but gun wouldn't cycle even tho he said it was good to go and he fired it . I ended up taking it back apart and fixing all the issues myself. The adjustable gas block was installed off alignment and not adjusted correctly.

do you have pics of the cases and a pic of the bolt face of your bolt carrier group ?

Have you tried adjusting the magazine feed lips so the bullet presents nose up rather than nose diving

I agree with everything said above.
But, I want to add something, break it down in to bite size pieces. Identify where the problem is not. Then break it down again, only in the area that problem is.

If you reload, try factory ammo. If you use factory, try a different brand.
Also try manual feeding (no magazine).

This is what I do when troubleshooting something and find my self scratching my head.

deleted by Laelkhunter

Many good suggestions, If it locks up manually feeding the round from the magazine, it is probably not a gas system, buffer, recoil spring, buffer tube issue. AR-10's can be problematic but the first thing to solve is manual feeding.

pavementends said:

Many good suggestions, If it locks up manually feeding the round from the magazine, it is probably not a gas system, buffer, recoil spring, buffer tube issue. AR-10's can be problematic but the first thing to solve is manual feeding.

Click to expand...

This is the first thing I did when I built one from scratch. Load one round in mag cycle to load and set in cradle so you still have the recoil, pull trigger and see where spent case land and if you have lock back of the bolt and a perfect ejection then move on from there.

OP has a duplicate post, https://www.longrangehunting.com/threads/jamming-up.365021/#post-3159241

jhites said:

My AR-10 which was recently assembled and is jamming up. It is slamming the bullet and putting a very large bent in one side of the casing, almost piercing a hole in the side. I have cleaned it tried oiling it ( helped for a few rounds. Pulling it back and letting it load it is jamming the bullet in so hard that i have to smake the butt on the ground while pulling back to get it to eject. Does anyone know what and why?

Click to expand...

If this happens on round insertion, start with checking the chamber, then the ammo. Since this is a new build you may have several hidden issues. No mil spec on the ar10 platform. The two biggest issues I've seen here are undersized/improperly finished chamber. (Some manufacturers undersize their chambers for a tight fit.) And ammo not sized correctly. Having said that, you may find using a small base sizing die fixes the problem. Separate the upper from the lower. Remove the charging handle and bcg. Hold the upper on a bench-muzzle down. Take a couple pieces of your ammo and try feeding into the chamber. Does it feed or sticks part way in? If so, here's your problem. If the ammo inserts completely by hand, you have a feeding issue. Feeding issues can be a bear to wring out. Who made the parts, specifically the upper, barrel, and lower? BTW, hard round insertion is a MAJOR SAFETY concern due to the floating firing pin. Be very careful wringing this issue out.

Last time I saw one with this issue it was 100% that the lower was out of spec, the mag catch wasn't holding the mag high enough to feed. There is a fine line between as high as it needs to be and too high, but it can be really low and still have the bolt catch the top round in the magazine. Sacrifice a magazine, cut the bottom of the mag catch hole down, rest the rifle on the magazine so that it is 'over inserted' and try it. If it gets better cut some more, if it's fixed you can send the lower back or modify a mag catch by filing the bottom off and soldering a shim on the top.

I have run into this issue with 350 legends in AR15. Found out if I polished feed ramps and bottom half of the exterior bolt face it cured the issue. Some finishes are pretty rough not allowing case to slide up into bolt then causing bullet to enter top of chamber. On a bottle neck case it's usually not an issue. If you notice bullet deformation or severe bullet runout I would try polishing above spots with a small dremel polishing bit and jewelers rouge.