Just spent the morning down at the range with a couple of mates and my Ruger #1 in 303 for final load testing. Two things I have found out about this rifle. 1. It is very sensitive to the way it is held when shot. If I hold the fore end of the rifle with the back of my hand on the sand bag, it will shoot very well. If I just let the fore end rest on the sand bag and tuck my non trigger hand under the rear of the stock, the groups go to hell. (3"+)
2. It is very load sensitive. My best load and the one that I will be using is 45.5 grns Reloader 15 with a 150 grn Sierra set 40th off the lands. 3 shot groups average 1" with the best one going 1/2". 45grns of the same powder goes out to 3". 180 sierras with 42.5 grns R15 shoot 1 1/4" Ave. 43 grns of the same powder strings them 3 1/2". It does not like the 180 sierra RN.
It goes without saying, "These loads were safe in my Ruger #1, please work with caution.

Good luck.

Wayne