Originally Posted By TrooperKbC:
Originally Posted By oneshot_onekill:
The barrel can definitely move around if it's not tight enough. I had a friend who asked me why his front sight was canted one day at the range. I quickly deduced the whole barrel was twisting back and forth! It would move a good quarter of an inch off center and yet still function. I never looked at the end of the gas tube inside the receiver but it was probably jacked up. Not to mention what was going on with the pin in the top of the barrel that aligns with the notch in the receiver! He sent it back to the maker and apparently this was not an uncommon problem with barrels that were completely MELONITE coated... Inside and out.
I would like to have taken it apart to see what was going on but it was a relatively new rifle and was completely taken care of by the manufacturer. He got a whole new upper. Even though he had run at least 1000 rounds thru it.
This is a rediculous claim. The interior coating of the barrel has no effect on installation. If the thing is turning within the receiver there is a problem other than the coating, such as manufacturing tolerances of the receiver and/or barrel extension. There is an indexing pin and notch that prevent twisting and the barrel should not be moving around without a good bit of force with or without the barrel nut. I have a completely melonite coated barrel and I have to hammer on it to get it out of the receiver.
My understanding is that if you melonite the barrel and barrel extension after they have been mated it will often cause issues. They should always be melonited separately and then put the extension on the barrel.
Torque your barrel to 30 ft lb three times (with grease on the threads first). Then attempt to reach the next hole, if you reach 90 ft lb (60 ft lb on Troy TRX and MI SS 2 barrel nuts) and are not close to lining up you have a couple of options.
1.) Try a different barrel nut
2.) Cut the lug blocking installation of the gas tube - not the preferred method
3.) Use an upper receiver lapping bar to slightly cut back the front of the upper. This works well, but you don't want to remove much
4.) You can probably do the same as 3 above by using a fine sandpaper to remove a couple thousands from the front of the receiver. If I was on a really tight budget I might try this.
5.) Attempt to torque the barrel nut over and over until it finally lines up within the torque spec. This might work if its really close to lining up.
You could always just turn it until it lines up, but you may break the upper.