Loading BP for a Marlin 1881 in 40-65

[Roosterman]

 The groove to groove on the rifle measures .410 It won't chamber a round loaded with a .410 bullet. It will barely chamber a .408, it's really tight. It WILL chamber a .406 with no problems. Seems like a tight throat to me. So, do you darkies think a .406 will punch up to fill the grooves with a full case of BP?   I know the only way to find out is probably to just do it and find out, but I'd like to hear others experience with this sort of dilemma. I'm shooting 20-1, I could cast sofet bullets if that would help the bullet to punch up.

[Ranch 13]

 Might want to do a chamber cast and get a good measure on the bore and groove diameter. But by and large those old 40 caliber rifles used 403-406 diameter bullets.
Those rifles were built for blackpowder so yes it will still work just fine.

[Roosterman]

The barrel slugs at .410. I'll let yall know when I shoot it.....