I purchased this AR upper from Gunbroker a few weeks back and took it out a few times to hunt some prairie dogs and zero in the scope. I was cleaning one day and after wards I chambered a round (in a safe direction) just to make sure everything functioned correctly. After ejecting the one round I noticed there was a pretty good sized dimple on the primer. I have read that this could be normal with free floating firing pins however my old Bushmaster upper never did this. After further examination I saw that the barrel nut was not tightened enough and therefore pushing on the gas tube causing the bolt carrier to bind up on the gas tube too early causing the firing pin to slam forward prematurely. After taking it to a local Gunsmith he reindexed my barrel nut and the gas tube worked perfectly. When I reassembled the BCG and tried to insert the bolt into the lugs it would not go in and in fact I had to fight it to go in and lock. Once in and locked it took an act of congress almost to get the bolt out of lugs and release the BC. So I took it back to the Gunsmith and told him to fix whatever he did. He said he took everything apart and the only thing he could find wrong might be barrel related. He then lapped the bolt for it to be able to go in the lugs but even then it still binds just a tiny bit.
So I turned on some bright lights and noticed that the barrel extension had somehow tweaked a micrometer clockwise as you look in the receiver from the back. The barrel extension turning clockwise doesn't seem conducive to overtightening though as the extension in relation to the barrel night would be counter clockwise. I am sitting here scratching my head wondering how this happened. How does the barrel extension get wacked out different from the receiver? Could the receiver itself be warped?
The Gunsmith said after more rounds things will smooth out but to me that means the bolt will just shave metal until its just reemed. It also means that if I put a replacement bolt in there it too may have troubles. I have a stripped upper receiver laying around that I was going to use for a different project. Should I just see if I can get everything swapped over?
I just don't understand how this could happen unless the receiver or the barrel index pin got bent or something. I am actually considering just getting a vise, blocks, and a wrench and mess with it myself. I can't imagine its that hard to do and it beats paying service charges.
What do you guys think?