I've swapped out the .50 GM barrel for the original Italian-made .54 for the coming weekend's trip to the range. I plan to shoot 390 Hornady GP-HP's. Sabotloader has warned me they will be snug and need a short starter. What charges do you guys suggest I try with this combo if I'm going to shoot 20 or so rounds, 10 at 50 and 10 at 100 yds.?