If it is like the 500, it is simply fine threads with loctite. A strap wrench with soft rubber strap is a great tool. If it doesn't forfeit grip, simply do a full field strip and put receiver and mag tube in the oven at 200 or so while a wet wash cloth sits in the freezer. Take out the heated parts and quickly wrap the frozen rag around the tube right at the receiver for a few moments. Then get the strap wrench back on and it should spin out fairly easily.
When you install the new one, I suggest the never seize (silver grease) rather than thread locker.
Brent
