RE: Working up a load – Advice
The first question is, do you have a performance goal in mind? In other words, if you need a fast flat load it doesn't matter if the bullets group at 80 grains powder as this will not meet your goal. Maybe you start at 100 gr and immediately switch bullets if one doesn't group there. If you just want the most accurate load possible, I'd start at 80gr with every bullet and work your way up. I killed a ton of deer with 80gr and a 240gr HTP out of my old sidelock, with no noticeable lack of power.
You can get bullets from Precision Rifle running up to 240 grains in sabots for the .45, they have a 260 grainer but it's made for the faster Savage.
My main question is what is the twist in this gun? It's not one of the .45s made with a 1-20" twist, is it? Those ones can be a bugger to find something that will shoot, there's a reason the 1-20" fad only lasted a couple years.