For deer, there really is no reason for 300 grain slugs. A good 240-250 grain will sail right through any deer and keep going, with a proper load. Plus the lighter recoil will aid in precise shooting, as I don't know a single person who shoots a harder kicking gun better than one that recoils less.
Keep your loads in the 1000-1200 FPS range and you will be fine.
I would focus on a single powder.
Say Unique, Titegroup, Longshot, or W231/HP-38.
Don't fiddle with trying 3 of one powder and 3 of another.
Pick something like Titegroup, and load it up in 3/10 grain increments from whatever starting point you choose. When you see good groups (not just one, but a few good groups), confirm it. Take a bunch out and validate that your load is indeed a good one and not just one or two good groups.
Great advise.
I would add CFE Pistol into the mix.
The fiddling with powder made me chuckle. I have a friend that showed up with 8 loads of different powders and bullets for his 45 Colt at the range. I just shook my head.
