ths78
Please do not use over 120 gr of 777 or Blackhorn 209 in that gun as more will be an over pressure load that could be devastating.
A 150 gr load of most powders is so far past max efficient load that mostly while adding to the recoil and pressure because of the weight of the powder you gain very little velocity. The most feet per second per grain of powder is usually found around 85 or 90 grains volume, reasonable efficiency is still found up to 120 grains but most of the accuracy loads are found between 90 and 110.
My personal method is to pick out several bullets I consider suitable and shoot groups with them on separate targets, one group per target and save the targets.
Then do the same at 100 and 110; them if any are constantly improving with more powder I consider using 120 for some groups. When I find a load I like I try 5 grains either way. I set two standards, one for hunting and one for target and competition shooting. I usually try the 40 caliber bullets 200gr Leigh and 200gr Shock Wave and the FPB in one batch [the 50/40 is for long range the FPB for states where sabots are not allowed; the next batch is the 250 gr bullets starting with the Gold Dot the Shock Wave and the 250 Lehigh. If I am planning a hunt for elk, moose or big bear then I also shoot the 300gr Gold Dot, Shock Wave bonded and several of the Lehigh bullets starting with the 270 gr group and working up to see what the gun likes. Having a plan and saving the targets so you can do side by side comparison is very helpful.