Jim in Houston wrote:For those of you who don't have the "exotic" materials lying around, I use Permatex Anti Seize Lubricant, which I got at my local mom and pop hardware store. It may also be available at a big box or from an auto parts store. It is commonly used on spark plugs to keep them from seizing, galling, or causing corrosion in the engine block due to the dissimilar metals. It will take the high temperatures, which the barrel nut / barrel will see.
You sir are a very smart man.
I use the same and it is my preference.
I'll try not to be too long winded, but my mind is coming back after getting my butt royally kicked by the flu.
For those who do not know, I am a forensic engineer/materials engineer and I do some firearms design as a consultant as well. Anyway, aluminum and steel have some corrosion potential, and, threads are cut on different machines, with different tools at different amounts of wear. We also "know" that 35-85 ft-lbs of torque is "specified." I use the aforementioned Permatex anti-seize. I coat the first 4 or 5 threads of both the barrel nut and the receiver AFTER the barrel is inserted and indexed. Run the barrel nut on and torque to just past hand tight, remove. With either brake parts cleaner or acetone on a soft cloth, wipe away any excess off the barrel and shoulder of the nut. Then re-torque to about 35 foot pounds, loosen and repeat. Torque to 45 ft'pounds, loosen and repeat. Now you have one or two more torques to go. If you need a hole lined up for the gas tube, you have some constraints. As long as you can get to at least 50 ft-lbs, with this method, you will typically be able to have the best accuracy for normal shooting. If you anticipate high rates of fire and need CB to HB drift minimized, consider trying to get to at least 75 ft-lbs of torque. This method will typically give you about 1/2 hole space more on a nut for the same torque just slapping it on. BTW, I do the same for muzzle devices.
When you use anti-sieze and the three torques/release, you burnish the threads a little, knock off some high points and increase the clamping force w.r.t. the torque levels while also greatly reducing the corrosion potential. I have also seen a reduction in CB vs. heated bore POI shifts using this method. My current match rifle was torqued to 95 ft=lbs, has 5K on it and shoots 0.5 MOA with the tester 10x scope on it even after 30 round mag dumps!