MikeRC, there is more than one Boeshield product. You are referring most likely to the rust remover, not the protectant. I got a small bottle when I ordered a gallon of the protectant. I haven't tried it yet, but when I do I'll let ya know how it works.
I had a party here last night. I fired the cannon a few times, wiped the bore quickly with water when I was done, and left it that way overnight. This morning between 6AM and whenever I became permanently conscious (noon-ish maybe?, good party) we had a thunderstorm that dumped over 4 inches of rain.
I wandered out there to give it a good cleaning after the sun came out. The waxy film left by the boeshield was still there, looking as good as it did yesterday.
After I ran water thru the bore, I swabbed out the bore and the vent with Ballistol (one of the best black powder gun oils in the world in my opinion).
Some of the Ballistol ran over the barrel near the vent and turned the Boeshield to a gooey mess. I left it alone and it eventually sort of hardened. It probably needs to be re-Boeshielded in that area. So, there is a bit of incompatibility between the two chemicals.