The original British standards are for a 400 grain bullet over 60 grains Cordite for 2,125 fps in a 30" barrel, and 16 tons BaseCUP. I'm currently using new Bell cases, Federal 215 primers, 400 grain Woodleighs, and 1.5 grains Dacron fill over 68 grains Reloder 15 for 2,075 fps in 26" barrels. Be sure to slug the bores. Original factory drawings for this shell show a .411" bullet, but a tremendous number of the guns are .408" in the grooves, including mine. Bullets of both diameters are available.