Out there I tried to load a .503 and using my thumb could not get it onto the muzzle. I was thinking.. should I take a ball starter and drive it in or just forget it. Since I was out there to shoot sabots, I decided I would stick with what I was doing. I have some of the MMP HPH-24 and some crushed rib. I will give each of them a try. I also have some of the standard Nosler sabots which might work real good...