In the mid to late 80's, I loaded for a full auto Mac-10 in 9mm with a suppressor. No subsonic ammo was commercially available at that time. Heck, 147's weren't either!
AA N0.5 was the powder I used with data from their big RED manual. The 2 bullets I used were the Sierra Tournament Master 130 grain intended for 38 Super, and Hornady's 158gr JHP. I was only dealing with a 6" barrel, but it was hard to stay below the speed of sound! WW231 wouldn't function the heavy bolt that slow! At the time I had a Marlin Camp 9 too, those loads didn't seem to have the "crack" of regular 9mm ammo in that 16" barrel, but I didn't have a Crony yet.
The 158's should have been more accurate with better barrel fit and more bearing surface, but at 50 yards a 5 round burst (from supported kneeling) the 130's were half the group size. 130's=3", 158's=6" Without the suppressor, all full auto groups were about 12".
So if you don't need the extra energy to knock down steel plated you might look at the 130's.
Ivan
