Enfield No1 MkIII has a slugged bore diameter of .314, and the No4 Mk1* is .312.
Beyond my understanding, shooting PPU 303 ammo through both showed the No1 to be pretty darn accurate, while the No4 groups being a bit worse. I thought I hit the jackpot having a tight bore on the No1, but slugging showed otherwise. The PPU jacketed bullet measured .311.
Since the bores are markedly different in size, I assume the Lee mold (the 160gr gas check variant) I have isn't going to work well in the larger bore of the No1.
What molds have shown to be accurate in Enfields with bores such as these? As a side question, can a gas check boolit function well without a gas check?