The T.C. book that came with mine said 1 in 28 twist,mine works best with 90 TO 100 GRS. of powder with 451. 45 cal. pistol bullets Speer or Hornady xtp200 to 230 gr. hollowpoints in a black mmp sabot, I have shot bigger bullets like the 300 gr plated soft point 451. 45cal bulletwith the mmp long petal black sabot and got very good grouping. I took a bunch of deer with it and a few hogs. I shot a big boar over #300 one morning with one of the 300gr. sabot rounds and 100 grs. of 777 powder at about 30 yards. I was leaning on a old rotten whiteoak stump and he walked right by me. He fell stone dead in his tracks, the bullet hit him right behind the neck in his backbone,and went all the way through. Just about all the deer had passthrough shots unless the bullet hit backbone or a double shoulder shot. I had mine drilled and taped for scope mounts and had a scope on it but took it off. It just looks better without one.