I ordered a Spikes Tactical barrel for my first AR build. When it arrived, I tried to fit it into my BCM upper, but I can't get it to fit at all. The barrel starts to go in the receiver and then sticks. The last time, I could barely get it back out. Is this normal? could my receiver have size issues? Everything else fits fine (lower, BCG). Do I need to grease the barrel first? Get a hammer? Get a new upper? Any advice would be appreciated.