The lack of forward assist should have no effect on function. So what exactly is the issue? The rounds dont chamber completely? Not riding the charging handle is more critical on these guns then an AR-15. Lastly you say you did not have the upper milled. I believe that mod is for magazine to fit correctly. Perhaps even though they are fitting it's not the correct fit. Just a few side comments. These .308 like to run with a lot of lube when new, dripping until they settle in. Has the headspace been checked? Ive attached a pdf of the upper mod for those who havent seen it. Definitely try different ammo Thanks for signing up!! 533_.pdf