Hey there Neon.
I have a Kimber Custom with the fixed sights and it is easily a 1" gun.
I found that the most accurate cast slugs are the 185-200 swc regardless of who made them. I actually came across 1000 of the swaged speer 200swcs and I save them for special occasions when money is at stake.
If you want a good jacketed round, find the Rem golden saber 230 heads with some power pistol.
They should group under 1"
Cast round nose slugs seem to be the least accurate in my gun.
For factory, the Armscorp 230 ball ammo is quite accurate, as is the wolf, but I don't trust the steel cases.
I have 3" 50yd groups with the wolf off of a rest.
I have been shooting Green dot for target stuff and Power Pistol for heavy loads.
I went up to a 20lb spring (the factory is 16) and that was about it.
Oh yeah, a lot of times I'll take the cast slugs and coat them with Lee liquid alox to reduce the already minimal leading.
My 18 cents.
Good shooting.
Tom