Ok, so here's the deal. Today, when assembling and attaching a barrel to my ar-15 upper receiver, I came across a problem. When pinning the gas tube to the gas block, I made sure that the holes in the tube were aligned with the block, and used needle nose players to hold the roll pin in place, and started hammering it in with a small hammer. Well I got it about halfway in and something seemed wrong. I checked, and the pin had gone in and held the tube in place, but the tube had twisted somehow. I now have an un-aligned gas tube, still pinned in place somehow. How can this be?? The initial inserting of the gas tube roll pin was not difficult, and it did not seem like it pushed so hard that it bent any gas tube metal. Please help me out. Call me a newbie to ar-15 construction. I've created lowers and can easily do that, but this is my first upper. Thanks.