To be completely honest, I've never shot any lead bullets through my .45 Win Mags. I could, simply haven't. (and just to be on the safe side, not going to shoot any through my Wildey, and "safe" in this case just means not gunking up the gas system
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Using an alloy suitable for 1200-1500fps, it should work fine in the .45WM. The Grizzly is recoil operated, so cast bullet concerns are the same as they are for smaller autos. The right alloy hardness for the velocity, and resist deforming during feeding/ not catch on the feed ramp.
Never used 800X (never even thought of it), sorry.
I measured some rounds from my last two boxes of Win factory ammo. (and its been decades, but I still don't feel right looking at a 20rnd box of PISTOL ammo!! All pistol stuff should be 50 to a box, like it was when I was a kid!!!
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1.570" seems to be the max length, 230gr FMJ and 260gr JHP, most were .002-004 shorter. The longest round I checked was actually one of the 230gr ball rounds.
If things go well, (and I'll know a bit more by Monday) in a few weeks I should be meeting and shooting with a fellow who has an Automag IV in .45 Win mag.
I plan to take the Wildey, the Grizzly, and my Contender 14". should be an interesting day!