My more recent Model 1886 Winchester .45-70 lever action "Short Rifle" from BACO/Miroku
has a 20"-long round barrel and 1:20" twist.
I slugged it and found a groove diameter of .457".
It will handle cartidges up to 2.800" COL, loading through the gate, feeding from the magazine.
The Hornady 480-grain .458" DGX Bonded can be loaded, crimped on the factory cannelure, for COL 2.785" in .45-70.
Since it is .450" diameter and smaller ahead of the cannelure, it works fine in the no-throat SAAMI .45-70 Gov't.
Just like JFE said about selecting cast bullets for bore-rider noses.
If using the steel-jacketed .458" DGX in the .457" grooves,
just for fun I might push them through a .457" LEE sizer and leave the lube on them
before loading, with a wax paper, milk carton, or playing card wad over powder.
For hardcast, FNGC, powder-coat-painted bullets in similar smokeless loads I would size them to .459" bearing with bore-rider nose.
No need for a .45-90 that way.
That even kills my desire for a .450 Alaskan.
BTW the BACO Winchester 1885 High Wall .45-70 Gov't. has a groove diameter of .457" also, but 1:18" twist, 28"-long octagon barrel.
That one is a 2010 model year.
