I just picked up several boxes of Makers 425 gr sub-sonic bullets. Talked to Paul he gave me a start load using AA #9 there's none available around me. He tried 296, it just wasn't that accurate. I have a bunch of Enforcer its little slower than AA #9. My main concern is close to 100% burn, I'am using a Ruger American with 16" barrel.
There's not enough room to use Trail Boss, seating bullet out to rifling only can get 8.6 grains. 12.5 gr. was getting me with CEB 250 gr. Raptor pistol bullet with a tip 1050 fps. at 30F elevation 780'.
If someone has access to Quick Load let me know what perimeters you need.