From the day I bought this gun I've never been able to get decent groups with 150 grain bullets. It did ok with 140s, and eventually I tossed in the towel and got a new barrel. So with the new Pac-Nor 3 groove installed I went about working up loads with 150 grain Nosler Ballistic Silvertips and couldn't get much better than MOA with a few different powders and seating depths. That is, until I tried Retumbo. The first group I shot was under 1/2 moa, and the second was just a hair bigger. I've shot a few more groups since then and it's consistently around 1/3 to 1/2 moa at 200 yards. 67.0-68.0 grains is where I'm finding success. I know these groups aren't stellar by some of your standards, but hopefully this info can help someone that's having trouble getting 150s to group.