-A wonderful christmas present but I am having trouble removing the stock to add a sling mount. The receiver extention nut will not budge. I purchased the special tool to remove the nut but no luck. Any suggestions?

You have to really torque that nut to get it off since it's staked on. After trying unsuccessfully to remove mine with a CAR wrench I finally wrapped a piece of electrical tape around it and then clamped on the largest vice-grip I own. It then came right off.

Some people here suggested that I use a punch to remove the staking, but I was afraid of missing with the punch and marring the receiver. In the end I would rather bang up a $3.00 buffer tube nut than risk scratching an expensive receiver.

Edit: Congrats on your 6400C by the way. Whoever gave it to you has excellent taste [:D]

I'll try again! I just don't want to mess anything up. The rifle is just too wonderful (and new) to screw anything up! My wife is the one with the good taste-with a little help from me!

Just be sure to support the lower as you are torquing on the nut. Once you get past the staking it will spin right off [:)]