Done?  Only you know this answer.  I bet with some work you could easily get 3″ at 100 yds or better.

If you have not slugged the barrel, you need to.  Once you know you have the right diameter bullets you can do some testing.  You can try different powders, amount of powder, different primers, different primer seating depths, different bullet weights, (lighter bullets will cause less pressure at the same powder charge than heavier bullets) bullet seating depth, and different neck tension.  If you think you need to roll crimp do it as lightly as possible. I like to taper crimp. Remember, your 45-70 barrel twist rate is probably for 405 grain bullets or lighter.  If you want to save your arm use 300 grain.

Start by experimenting with your powder charge to find the most accurate groups. Do not go over the normal FPS. Watch for pressure signs. 

Once you know the best powder load try different bullet seating depths.  Seat your bullet long so that the cartridge won’t slip into the chamber then start pushing the bullet in .001″ at a time to the point the cartridge will load into the chamber. This is now the spot you don’t want to go any longer only shorter. The bullet is just off the lands.  Now start shooting groups at different seating depths to see if you can find a sweet spot.  Start with big jumps like .005″ at a time.  Start at .040″ of jump/leade and work down.  You need to watch for signs of pressure. 

If you are going to load the ammo through the magazine you will have to start this process at the max length that will cycle through your gun instead of where the bullet touches the lands.  Some people will seat at .040″, .030″ then .020″ off the lands.  One spot will almost always be better.  If one is, start loading in and out around the length .002″ at a time.