Two Bears,
I use a regular powder measure that goes from 5 to 120 grains and set it at 90. I shoot at 90 grains for all my rounds from 215 to 330 grains. The rounds that I use are from the people at precision bullets and I get great accuracy with it.
However with a 300 grain bullet from another supplier I used the same 90 grains and the group really opened up. I would start at 80 grains if I were you and work my way up in 5 grain increments to see where my groups opened up. Shoot 3-5 round groups then increase your powder load by 5 grains and shoot another 3-5 round group. When your group opens up then go back to the previous powder charge. Make sure you record on a small tablet what is going on with each round of groups. That should get you to where you want.
I don't know about the encore, but I have an Omega as well and you will love the BM3 in the Omega.
Paul