I recently got two 54 cal. barrels from Bob Hoyt, Bob said they measured .540 bore, and the grooves were around 8 thousands deep. Now I was looking for the right size for pure lead conicals, I need something that I can push down the barrel, but not too loose. I was looking a bullets from the bull shop, but this fellow would not recommend a precise diameter. I do have some great plains bullets left and these will work due to the hollow base. The bull shop bullets are flat base, 420 grains. My barrel twists are 1/32 and 1/38.