Lee touches on a point that I don't think has been directly addressed. In a 50 cal ML, you shoot a smaller caliber bullet in a 50 cal sabot. These bullets are usually 40-45 caliber. I only mention it because I nearly bought a 45 caliber sabot/bullet combo for my 50 cal which would have fallen in the barrel and been extremely unsafe. If you purchase the sabot/bullet together (like your picture of the hornady SST) 50cal=50 cal. If you get creative and buy them seperate you'll likely shop for 45 cal bullets and 50 cal sabots. Seperately purchased sabots (MMP & Harvestor for example) will list the bullet diameters that the sabot can handle.

Tom