A 3/8 ramrod will go down the barrel...
I converted my .45 to a .40 when I built a .54..A .40 is great on squirrels when you drop down to 25-30grs of FFF powder and can be stoked up to say, 60grs FFF for larger game, deer inside 50 yards, coyotes, foxes, raccoons, etc...
A .390 ball also bucks...