A guy on another forum said that it could be a sharp feed ramp on an ar15 barrel causing it. Some Cases have dents half way up the case.
Thanks for the opinions.
Good luck.
Seems a good look at your chamber is a good first step (lotsa light)
If nothing obvious many separate the upper and try approximating a feed from the left stack and the right.
Also might try ejecting unmarred brass.
Happy New year!