[Thor]

When they switched to the salt or immersion bluing they blued the entire piece that was being blued, in the case of a barreled receiver that would include the inside of the bore and inside of the receiver forks, everything. It is hard to plug a bore that is being immersed in 300 degree F liquid for half an hour (actual time and temp will vary due to chemicals used), actually the bluing adds some bore protection as well. In rust bluing the max temp is 212 degrees F. I always plug the bores on rust blues but never with salt bluing. Remember als that if a 1937 weapon was before the "t" block is should have a rust blued finish if probably done. It appears from TRL, Jan Still's excellent reference that from the 1936 "n" block Lugers to the time when the 1937 "t" block switched to salt bluing, that this range of Rust blued Lugers did NOT have the interior surfaces polished as before, an important fact to remember. The muzzles on post 1937 (salt blued) Lugers were left in the blued state when issued. I am sure that upon firing them, some of the bluing is burned away and the holsters and other adjacent objects may have also worn some of it off. Thor