I found a Marlin 1894 CB in 44 mag with a 24" barrel manufactured in 2003.

I suspect it has the 1/38 twist.

I want to shoot 300 grain Hard Cast bullets in it and I am seeing where from others past experience that
it takes a .431 dia. to get good accuracy otherwise their cast bullets were key holing.

Anyone here have experience with this bullet weight of 300 grains in the 44 mag 1/38 twist?

I am hoping for accuracy......

thx,

Have you slugged the bore? Check the diameter and go from there.