17 Fireball (17 MachIV)
When I got a Cooper MIV, I got a box of ammo from Cooper. It was 20 gr VMax. Was told powder was 19 gr H-335. I loaded 100's or rounds to this spec and shot most 100 yd groups in the 1/4 to 1/2 inch range with 20 and 25 gr Bergers and Kindler's 25 Gold bullets. For H-335 start at 18.5 @3300 to 19.4 @3800 fps with 25 grainers. All of these with Rem 7 1/2 or Fed SR Match primers. Also had good results with H4198 and V133. In small caliber cartridges, pressures rise rapidly with small increases in powder. Go slowly and be safe.