I tend to favor 900 to 1000fps but have loaded a few ight loads for my GP100s. I had a bunch of 210gr RNFP from SNS Casting and have used 5gr of HP38 for about 725fps. 5gr of Trialboss gets about the same, possibly just a hair more. I have loaded what was known as a galley load using .430/.433 round balls over 3.2gr of Unique for about 500fps. These are really low pressure and may back the primer out. If that happens you can enlarge the flash hole. Its a dirty load but fun for the women, children and those that are still a child at heart.