I'm trying figure out the correct bullet size to use. The muzzle measures .426, which I've read is something colt did to barrels meant for .427 bullets.
The slug, once past the muzzle, requires only light taps the first three inches then can be pushed to the forcing cone with a pencil.
Pushing the slug past the forcing cone shrinks it to .423.
The cylinder chambers slug at .427. A 4255 bullet falls through the chamber easily.
There is full but shallow rifling on the bore slug and I can see rifling down the bore.
A loaded cartridge fits the chambers barely snug using .4255 lead bullet. A .4255 jacketed soft point cartridge (Winchester) will enter and fall out of the chambers. The bullet diameter is supposed to be .426.

The forcing cone measurement bothers me. I can't push a lead or jacketed bullet through it from the cylinder side. Won't the bullet be squeezed too much and rattle down the bore? I can't use a larger bullet in the chambers to match what I think the bore is, the cartridge wouldn't fit.

I'm confused here, maybe over thinking it?