Just experience...I used it the first year I had side lock (closed end bore) and come spring put a pull thru and it came Orange. It took most of the morning to get it cleaned out and barrel polished back up.
Maybe it works better in the in-lines with the breach plug removed and air can circulate.
Bore butter, especially the biodegradable natural stuff is nowhere near comparable to a CLP product like Breakfree for storage/presevation. Why not just use it, like you do on all your other barrels ?
take a read thru these comments on the issue;
https://www.shootersforum.com/muzzle...ased-oils.html