Well as for the bore butter, I prefer it in my flinters that use black powder. But in my inline and my percussions, I use Montana Extreme Bore Conditioner. Also, for cleaning, I use the hot soapy water for all my traditional rifles but in my inline, I use T/C's T-17 solvent. This stuff is great.
But after a thorough cleaning with either method, I always follow up with an alcohol patch the a dry patch to get all the moisture out of the bore. Then a light coat of Monatna Xtreme (or any good gun oil).
When you get to the range, get that oil out of the bore with alcohol or windex or you will have a fouling issue.
And always swab between shots - even if its only with a spit patch.
As for the charge, I agree with everyone else, lower it down. Being that you are using pellets, drop down to 2 (100 grs). And when they are gone, get yourself loose powder so you can adjust the charge to get your rifle's sweet spot.
Good luck