I think probqblly as good a rust preventive as you can get for inside a gun bolt, trigger mechanism etc, even outside the gun, is WD40. Spray it in and on and let it run off. The little that is left after the carrier evaporates will leave fish oil on the surface, which is an excellent anti moisture, lubricant, rust preventive. -- When one runs his auto through a water puddle and soaks the underhood area so wet that the ignition is shorted, simply spraying the wires and all ignition components with WD40 will chase the 'electric shorting moisture' out immediately and the engine will start. I've done this many times with the only distributors, taking the cap of and spraying inside, then the outside. The treatment will last at least a couple years, and that is pretty good testimony as to the moisture barrier effect of WD40.
If you happen to run a chinsaw or other two cydle engine, and if you use Sthl or Husky two cycle oil in your gas. Washing your gun parts in some of the gas oil mix and letting it dry will accomplish the seme end. I don't know about the effectiveness of other two cycle oils. but I've proven both the above, which are the top of the line performers in 2 cycle engines.
LBT lap compound will smooth up a gun bolt, but normally the roughness causing the hard action is too severe for this fine compound. Better to use something quite coarse, like medium valve grinding compound. Wash and rub both surfaces as clean as possible after lappping them and use a stiffer lubricant on the bolt sliding surfaces, than WD40. If you'll be exposing the gun to a lot of dusty conditions, stick with WD40, applied well in advance of exposure to the dusty conditions, and put up with slightyly stiffer bolt slide, for the benifit of a lube that doesn't attract dust.
LBT lap compound is available from LBT for $18,50 plus $6 postage. That postage will also carry a few other items like lap plates and push through slugs or some bullet lube. Email me, or call if you have further questions on it. LBTisAccuracy@localnet.com 1 208 267 3588 Email is best as I'm rarely by the phone, but if you leave a message I'll call you back.