Rem 350 Mag

If I wanted a tighter group and lower velocity, and the "too long" bullet length was a problem. I would not hesitate to use a good 180 grain bullet and work with the seating depth and different powders to find another node that gives the desired effect. You are pretty close right now.
First thing I'd do is reduce your powder (same powder) charge until you get pressure you can deal with. Then seat the bullet (same bullet) .010 deeper per group and just see how it looks then.