I use it in a mixture for patch and wonder wad lube.
However I never put it in my guns anymore. 6 or 7 years ago I used it as a final lube after cleaning in all my arms (air gun, smokeless, & Black Powder). Within 1 week - every one of those arms had surface rust in the bore. I don't know why this happened, but I know it happened and fortunately I caught it early enough to clean out the rust with bore paste before any metal pitting occured.
All of these guns had been cleaned, and then a patch of denatured alcohol run through them to dry out any moisture, then the Ballistol applied. All arms were then stored under climate control for the entire time. I can see no reason for the rust, but it was there and the only difference to my normal cleaning routine was using Ballistol rather than a gun oil for preservation.
Basic troubleshooting says that the most recent (or only, in this case) change is usually the cause of any sudden issue.