This is NOT so. You can use a .458 rifle bullet and a Black Crushed Rib sabot in MLers, they work in my Savage and in my Omega. They are "just right tight" in both guns. You can also use an Orange MMP sabot with Rifle bullets. Rifle bullets that are .458 are 45/70 bullets generally and they are PERFECT for MLers, velocity wise, stronger in general than the pistol bullets which were designed to expand at 800 to 1200 fps.
Chap