I also have a gun that will not function with longer/fatter/heavier bullets (they push into the rifling and jam). I ended up just buying .380 slugs which make a nice high velocity target load, very flat shooting. Anyway, you are recommended to seat 1.12 at 4.5 grains of BE powder for a 125 grain bullet as a rough load. I would say go down to 3.5 for your starting load, then, to offset the deep seating. Work your way back to 4.0, and I would not pass 4.25 without using some caution. 3.5 may not cycle the action, but 9mm depth adds pressure fast so better safe than sorry.