Slugged the 1873 barrel and

[FOTIS]

Looks like the 'Modern" Winchesters are .430" not .427" like the ones of yesteryear. I have a BUNCH of .427" cast 200-grain bullets.

I take it they won't shoot in my .430" bore?????????????

 

[JD338]

Probably not.
Marlin ran their 44 bore at .431" making costing accuracy with
.429" bullets. Hornady runs their 44 bullets at .430" so it may help with jacketed bullets.
Rim Rock Bullets in MT offers both .430" and .432" bullets so you might want to take a look at them.

JD338