Are you going to do this with a lathe? Or are you going to attempt this with a die and some sort of handle? Cause doing it without a lathe is pretty risky. The threads if your using them for a muzzle break or suppressor have to be exactly square to the bore. Other wise the item screwed on could end up crooked and the hole through it not line up.
I my opinion I would not do it myself and I thread pipe all day long. You can screw up your crown or not thread it on straight etc... I would just pay the 200 dollars and have it done.