Looking for advice on twist rate for a 300 ultra to shoot 155 to 168gr bullets.Have had 2 Rem PS and 1 Rem Sendaro barrel on the rifle with 10" twist and all three will shoot 180gr and up well. However when I drop below 180s, groups suffer and open up.I have emailed Sierra and they suggested an 11 or 12 twist with no preference for one or the other with these bullet weights. I am about to have a short throated tight neck reamer made and order a new barrel. Has anyone out there tried something like this???