So recently I had a parts failure on a Midwest Industries AK handguard and now my dot can't hold a zero on my AK74 (99% sure this was an installation error on my part) so while I was a bit bored today I was kicking some ideas around in my head about overall cartridge length and I decided to see if 5.45x39 rounds would work in PMAGs. And at least initially it seems like they sorta do. That got me more curious and I did a little research, a few companies have made 5.45x39 parts for ARs in the past. I would love to hear from anyone with knowledge on the subject matter about how this idea actually goes into practice. If there isn't anybody who can speak authoritatively on the subject I'd be happy to experiment a bit and try putting together an upper.