Hey Guys 1st post, anyway I've put together a few 5.56 AR's and decided to build a 300AAC now but I'm running into some sporadic cycling issues. About 1 in 10 rounds is getting stuck at a 45 degree angle going into the chamber. I've never run into an issue like this before with any of my 5.56 builds and after researching it sounds like 300AAC is a little harder to setup. I think I need a heavier buffer or lighter spring or both?? I run the gun suppressed and unsuppressed any help is appreciated, also my build is below:

SOLGW Upper/lower/Blaster guts
Mil Spec Adjustable Carbine Stock
Faxon BCG
10.5 Faxon Gunner Barrel pistol gas length
Standard carbine buffer and spring

What mags are you using? What ammo? Does it still do that if you change to a different mag, or a different round?

I've noticed my 300BO will do that when the bullets OAL is short. I think the Hornady subsonics were really short and tended to jump out the magazine as the BCG tried to strip the top round off, causing it to jam funky like that.

The only thing I changed on my 300BO was I put a Geissele super42 spring in and an H2 buffer. Thats it. It runs 100% otherwise, as long as I don't load those specific Hornady manufactured ammo. I have a sneaking suspicion that those rounds are intended for 300bo bolt actions. The oal is way short. I think they were the Vmax ones or something, I'd have to go find the box.

ETA Welcome to the forum. Pro tip: don't post a "hello, new guy here" post in General Discussions

Let's start with the ammo and mags as previously stated

I have both the Magpul and Lancer 300AAC specific mags and both do it, was shooting factory Winchester 125's today but like you it did the same thing with the Hornady subs.

I have a suspicion that moving to an H2 buffer may slow her down a bit and reduce the round jump.

I use Magpuls and Lancers too.

I only really shoot 147's and 200's in mine though. I don't typically shoot the smaller end of the 300 spectrum. I also make my own ammo, and my one experience with the Hornady 300blk rounds was not great.

I even had 150's with me but didn't cross my mind to try, oh well I'll clean her up and bring some different ammo out to try next time. I also think I'll give the Geissele Super 42 a shot with a H3 since that's what they call for suppressed, I'm running that spring in my 16" 5.56 already just don't have a H2 or H3 buffer to try so might as well take the $100 plunge.

Thanks for the help!

https://www.ar15.com/forums/AR-15/Troubleshooting/66/

Had a chance to try out the Geissele Super 42 and H3 buffer today and it shot the subs and 160 grain ammo fine but still doesn't like the 125 Winchesters. The cases are now ejecting to the side and slightly back so I think the over gassing is gone, will leave it as is and no more 125's.