I had this same issue of having to constantly use forward assist to chamber rounds in my 7.62x39mm AR. It is most likely caused by the casing of the round getting caught on the mag. I tried using a Dremel to remove some material where my mag was catching the cases and helped a little but still did not solve the problem. I then decided to get an H3 buffer and a extra power buffer spring to experiment with and after installing those and tinkering with the gas block I managed to fix this problem. Since then I've switched back to standard buffer weights and spring and the issue still hasn't come back yet, even with brand new magazines, so I think the solution all along was just a good break in, which I think the heavier buffer weight and spring probably expedited quite a bit.Like I said above, if I push the assist forward it will shoot more times than not. This is when I shoot steel cased ammo. I'm thinking that the bolt is not going all the way forward into battery.
Would a heavier buffer or stronger spring be the cure?