I have a 1874 martini that i converted to a 450 straight. We set the barrel back and use a 458win reamer, without the beld, i turned the belds of 458 cases, and load Lee 500 grn cast bullets, gaschecked, my load is 60grn Somchem S365, similar than IMR3450, velocity is in 1600fps range depending on cases.
I use slow burning powder to keep the pressure down, below 30000psi, the beld is turned down to
prevent using full house 458win ammo.
Has anyone tried this before?