So - .552" calibre using a necked .600 Nitro case?

What does 538 mean after the .600 in the .600/538 designation?

If 538 is bore size, then the rifling is .007" deep per side.

700 meters per second - for me, comes out to 2,290fps?
I make that at 8,409fpe. V x V x BULLET wgt.in gr. divided by the constant 450240.

I guess a person could always ask why. Of course, that's the beauty of the capitalist system, if you build it, sell it and make money, that's good business.

This gun makes just a bit less FPE than BigDogs 2 bore muzleloader that Steven Zihn built him, provided BigDog gets 1,050fps for velocity with the 3,500gr. ball.