Are you using reloads or factory new ammo? I have found that with a lot of barrels these days 5.56 and 300 that until broken in they wont shoot reloads. I had the exact sale experience that you are describing. In specific I was using a
Sota Arms 16" 1:8 twist 300 AAC black out bbl that I bought
Here
I was unable to find ammo so I got some reloads from my friend. The reloads would stick in the chamber. When I called my friend he said he was running them with no problem. We then checked the rounds with a chamber gauge and they rounds showed to be in spec. I then found a box of factory 300 ammo at gander mountain
Here but it is always sold out. The ammo ran fine. I then found the freedom munitions reloaded ammo
Here about 12 cases of 500 left.
The Freedom munitions runs great and I am getting 1-1.5 MOA groupings. I hope to get better in the gun vise.
I have been playing with 5.56 for a while and have had the same issue with my reloads not running in new bbls even when they spec out. I was told by one of the manufacturers that when they are reaming the bbls if you get a chamber that is on the small side of the specs and reloads tend to me at the max size then you will have problems until your chamber breaks in. He also told me that many ammo companies build their ammo to the small side of the specs or just under the small size so that there are no feeding problems.