9.3x57- the rifled chokes on the Paradox doubles were very deep indeed. I have some pictures of muzzles somewhere. The depth is needed to start spinning, a heavy projectile that is travelling in the 1,300fps to 1,500fps range already. A ratchet type of rilfing was also used, deepest at the bottom of the side of the groove that 'took' the most stress of spinning the ball(bullet), ie: right hand twist, left corner deepest.
: I think a normal full choke with a 1" to 2" end choke, if rifled should work fairly well. That would give .020" depth of rilfing each side.