(On powder varmint rigs) I have had good luck with the round ball stone on a dremel. However, the crowning of the barrel appears to be over rated when it comes to these Chinese barrels.
There is a wood stock (see below) available from Canadian Arms that is an easy mod to fit the avenger with a bottle. Prices listed are in Canadian dollars, so it is a little less $ in the US. KAC5STCK Kervan Arms C5/K1 Wood Stock