I have a No1 which I rebarrelled to 303/25.I put a 30 inch heavy octagonal barrel on it and a 20X Leupold .using 120 gr sierra HPBT it will shoot 1/2 inch at a 100 and sub MOA at 400.Its not a pretty rifle but its bloody accurate.I'm sure a 303 on a ruger No 1 will just as good as my experiment has .Sadly the 303 has not had a lot of good results over the years as the cartridge has never been paired with a good action and good barrel.

good luck with yours
sbs470