I picked up a cheap second hand barrel and figured i’d try making a complete. I then purchased a BCM upper. the barrel was non-m4, so i dremeled in the extensions to match the reciever, which ADCO said should be a snap to do. seemed easy enough and they look right on, and i checked with a tool inside the extension to see if there were any rough edges inside. well, I was getting ready to send out the barrel to get cut down, but thought i’d mate it to the reciever first just to check it out. I dont have the bcg for this project yet, so after assembly i borrowed a BCG from another gun to check function. Well, i try to send the bolt forward and it won’t go fully into battery, even when pushing the forward assist. the lugs go into the barrel extension but the bolt will not rotate. any ideas what the problem is? i dont want to send the barrel off to get cut if there is something wrong with the barrel extension. What are possible causes? it reminds me of what happens when a gun gets really really dirty and the bolt won’t seat. But, everything is clean and i can’t find any thing obstructing movment inside the extension. when everything is dissassembled, i can insert the bolt into the extension and it will easily rotate ito place. Help!
First check to see if is plugged in. Seriously, Check the alignment with the gas tube and the carrier key on the BCG. Then check to see if you have the correct length on the barrel extension. Next, prey that someone who knows more than I do can help from there. I only assemble uppers from new parts and it is my opinion that when you mate new parts with used parts, problems can pop up. Good luck.