I built the first on with a 1 in 10 twist and the second with a 1 in 9. You can push a 70 grainer to 4400 fps and a 90 grainer to 3900. I'm shooting a 90 grain Accubond around 3500 to 3600 fps now. I slowed it down a little, because the heat has quite a influence. I tried the new 107 Lapua Sensars L's and they shoot real good, but they are not a hunting bullet, so I'm using the Accubonds. I tried the Bergers with no luck. They willnot handle the speed.