Is it leaving cuts or scrapes in the side of the case?
I had a feed issue on a home build(not my build) AR. Mine had scrapes from the tip up the side of the casing. Jammed repeatedly manual and shooting. Also caused denting of the case if you used the forward assist and would also lock the bolt partially open. My problem ended up being a sharp edge on the corner of feed ramp on the squared corner. I used a needle file then a fine emory cloth followed by polished fixed my issue. Don't know if this will help you or not but it's at least something to look for.