I am in the same boat. Most of the guys I shoot with use around 14gr with a 190gr bullet, and in their experience, magnum primers are necessary.

I'm going to try and do testing this weekend with 180 and 190gr bullets, my plan is to try around 14gr to start

Went out and did testing this weekend. The groups on the right are both 3 shots, 13.7gr at 100yds. The top is a 190gr Brooks bullet, bottom is 180gr Paul Jones. By the time I got to 200 yards the wind picked up, but 13.9 seemed to do a bit better.

Also tested large rifle, large rifle mag, and large pistol mag over a chronograph. All 3 set the powder off no problem, but in 5 shot groups, the large rifle had 80fps spread, pistol had 50fps, and LRM was 15fps