In a sabot, sure you can do it. Make it any hardness you want. The thing with using soft lead naked projectiles in a ML is because it has to be small enough in diameter to load easily and soft enough to swell upon discharge so as to fill the grooves and provide a gas seal. There are exceptions to that rule, I'm sure, but that's the gist of it.
Then again, a soft projectile swathed in a sabot, will expand that much better upon striking the target than a hard one will. So why not use a soft one? I wouldn't take it as dogma, but it is a pretty good guide.
Also, oft times the really hard bullet in a magnum handgun (or rifle) is a detriment also. More leading is caused by gas cutting past the bullet (and melting the lead like a blow torch because the hard bullet didn't expand to fill the rifling) than by a softer bullet that does expand to fill the bore- all else being equal. Hard bullets aren't necessarily an enabler for high velocity.
Last edited by gnoahhh; 05/08/13.