I've got a GPR in .54 caliber. Its a 1/60 twist barrel. I'm assuming yours is as well, so round balls are what you want. I shoot a 225 grain, .530 ball with .018 patch over 80 grains of 2fg. I use the same load in my TVM Lancaster as well. Its got a 1/66 twist barrel. I prime with 4fg. I am getting 2 inch groups at 50- yards with that load, and killed a big doe with the Lanc this season. 40 yard shot and the ball went in one side and out the other. Dead deer.
Get yourself a Lee double cavity round ball mold, melt those conicals down and make some balls out of them.
If you had a faster twist, say 1/48 then I'd say use the conicals, but with the GPR it likes round balls.
Last edited by Blue Bird; 02-09-2017 at 11:47 AM.