I'm a little late to this thread but, I shoot Bullseye pistol as well. Our group did the same thing with the 160 magma swc. to reduce recoil. It didn't work for most. It is a short for caliber bullet and has to be pushed hard for accuracy at 50 yds. At the short line a charge of 4.4 to 4.6 bullseye seemed to be what they settled on. Most shooters either went to the 175 grain H&G 68 clone at 3.7 to 4.0 bullseye, or the 200 grain 68 clone at 3.8 to 4.2 bullseye range. I think the 175 is the shortest bullet you can use with light charges and still get accuracy. If you can get the 200 to shoot at around 4.0 grains it is a pretty soft load. you will have to adjust sights between short and long lines.
Crimps on starline and remington brass is .469. Crimps on thicker brass, I'm not sure but I would think around .470/.471.
Hope the info helps.
Tony
PS. crimps on match barrels make a huge difference but it is barrel specific not manufacturer specific. as well OAL.