My son’s M15’s buffer tube lock nut loosened up so I tightened it with the spanner wrench but now the charging handle rubs the top of the collapsed stock. I don’t think it ever did this before. My question is, "how does the tube maintain the right position so that the bottom is indexed at 6 o’clock (when I tightened the lock nut it appeared that the stock is slightly cocked to one side when viewed from behind the rifle). Does the index plate have anything to do with this adjustment?
More than likely the receiver extension isn’t straight within the receiver (tube is canted). This is one of the things to look for when installing a stock or tightening one up. This occurs a lot less with mil-spec sized tubes vs. commercial.
I’m not sure if I follow you. Are you saying that it must have been this way before because it’s not possible for me to install it incorrectly? I didn’t take the tube off. The lock nut was loose so I tightened it with the spanner wrench (while holding the tube with a strap wrench).
When you tighten the castle nut tightly it can cause the tube to spin ‘more’ in the receiver if that makes an sense. This offset alignment would then allow the CH to contact the now canted stock body. This happens to occur a lot more in commercial tubes and not as much in mil-spec tubes. The deeper bottom groove of the mil-spec tube doesn’t allow it to happen very often. The groove is deeper in the mil-spec tubes because of the complete threads that mil-spec tubes have.
I use a lower receiver block in a vise and tighten the castle nut and check alignment before staking the receiver end plate to the castle nut.
Thanks for the explanation Gotm4. Now I understand.