i have been using bore butter or maxi-lube as they called it years ago for 36 years now.i never had rust problem, i guess. i did notice that after i dried my hot barrel and bore buttered it, next day i found rust near muzzle. i dont think it was butter but FLASH RUST you talk about. yet, i dried barrel real good before i put butter in.i am leaning towards using SHEATH in barrel to store it.i believe that rust would not have showed up if i used SHEATH in barrel. i am still going to use bore butter to shoot my MAXI-BALLS and on my patchs on my roundballs.also i am going to still coat bore with bore butter during shooting andbetween shooting. but, if i am putting gunaway for months, in goes SHEATH.then before shooting i will swab out the shealth with alcohol patchs and wipe in bore butter and shoot. what do you think?