I started shooting a little B.P. in the 80s with my CVA then quite a bit in the early 90s . I'd always been told , and it was true , when you clean your rifle / gun , the next day check the bore and or just run an oil patch down the bore real quick now f your in a hurry , there will always be a bit of rust and by golly its true and ive always made that a habit . Some folks clean them then throw them in a safe of just hang them on the wall and forget about them , ive told many folks over the years about the " next day oil patch thing " . Any who ... When I first started building and for the first dozen builds , I'd often watch Hershel House build on his amazing 1991 building VDO . Well , in it he just uses motor oil when oiling his rifle after cleaning it . Once after cleaning I used motor oil instead of the gun oil to swab the bore . As usual the next day I did the " day after wipe " ....no rusty bore ... Hmmm , Thats a welcome but strange occurrence . Then it happened again and again ... Since using motor oil ive never , knock on wood , had the rust patch the next day , need to run and oil patch , occurrence happen again !! Thats no B.S. Only thing I figure is ... That modern oil is d@mn thin , and it isn't intended for a B.P. firearm . That B.P. is darn corrosive and just sucks the moisture out of the air and rusts up your bore . Even before my motor oil experience I noticed the bore rust was , naturally , always worse in the humid summer . No dont make that motor oil patch a dripping mess just some motor oil on the patch and run it to breech and back , wipe the muzzle if any excess ... Check it out , see what ya thick . My trade gun barrel bore is shiny silver . Take care