I've been using bore butter since forever, NEVER had a problem with it. I've posted this story before.
Some time back, I was at a Fall rondy and shot a course of sixty rounds with my T-C Hawken. For whatever reason, I didn't clean it after the shoot, figuring to do it when I got home. I simply ran a patch with a good gob of WL worked into it down the bore. When I got home, I learned that my daughter had a medical emergency and was in the hospital.
She was only in overnight, but we had a bad scare and most everything except her well being occupied us for quite a while. Six months later, I remembered my Hawken leaning in a corner in the garage downstairs.
I heated a pail of water in anticipation of cleaning a ruined barrel. I cleaned it the same way I always had, in very warm, not hot water with some Ivory soap grated into it with a cheese grater. After I cleaned it, I looked at it with a bore light to find no damage whatever. Then I ran a final WL saturated patch down the bore and put the rifle back in the rack upstairs. That was about six or seven years ago. I use WL 1000 or lard to grease my patches, whichever is handiest at the time and WL 1000 to grease the bore after cleaning and under all the metal where it lays against wood. No problems.
Three Hawks