When I started bluing in 1983, I started with Brownells salts and used them until I quit bluing about two years ago. That warning that Brownells published, made a lot of sense to me and I never even thought of plugging the bore ----ever! I blued hundreds of rifles and I doubt any damage or pressure increases took place. My thinking on the bluing solution inside the barrels disappeared on the first shot through the bore. I also doubt that it improved accuracy either, but plugging the bores definately improved my chances of burning the crap out of myself and everything else.
I knew a dumb-ass that splattered hot (292 degrees approx) bluing salts on his bare arms while bluing that left permanent disfiguration on his arms.
I don't know for sure, but I doubt the gun companies plug the barrels either.
I have shot unblued barrels many times after installing them. Before bluing them. Some I sighted in after the rifle was completed and I didn't see any differences in groups etc.
All I know about this subject is from personal experience, I do think that Bob Brownell knew what he was talking about.
