I shoot that same bullet (the Lee C185-312-1R) cast from pure WW and run through the sizer at .312 to seat the gas check. The sizer barely touches the bullet. I tumble lube with LLA and shoot over 19.0 gr of SR4759. As Gunboat stated, I too get 1.5" groups at 100 using peep sights.

Slug your barrel first and then choose bullet diameter. You want the bullet at or 0.001 over bore diameter. I've tried this same bullet in one of my 1917s and it does well. The Lee C200-308 shoots better in my '03A3.