Mike:
I shoot a lot of black powder in cartridge rifles in competition and use Swiss powder exclusively. It is simply, IMO, a superior powder for the cartridge rifles games, both silhouette and Creemoor.
Howsomever, Goex makes good powder and I would think that it would do anything in your double that any other powder would. Goex Express is also good powder, somewhere in between standard Goex and Swiss. I was given some for testing before it was on the market and I was favorably impressed.
Other folks have been reporting good success with recent lots of KIK and Schuetzen powder, but I have not worked with them.
FWIW, Graf will sell Swiss in small quantity, but there is still the $20 hazmat fee.
http://www.grafs.com/powders/3522 What the intended use of the load has some bearing on what will be the best powder. Are you looking for maximum velocity? Loading for a double rifle would be a most interesting challenge. Besides everything else involved with finding a load your rifle likes, you need it to regulate as well.
Don't be afraid to shoot real gunpowder. You will be amazed what can be done with it.
Glenn
