PREDATE, the only smaller calibers I know of are all round ball shooters - .32's, .36's, .38's and .40's. They are fairly short range propositions with the two smaller ones pretty much limited to 50 yards and the larger ones to 100 yards.

MMP makes a sabot for shooting .357 bullets from a .45 caliber gun. (http://www.mmpsabots.com/blue.html) I've tried them in my 1:30 twist barrel with Hornady 125 grain XTPs and got great accuracy with light loads, but couldn't get them to shoot well with hot loads. They were just not long range shooters.