Greg, it could be many things during manufacturing. Old equipment, hull material, thickness of the rim, lots and lots of things.
FWIW, a friends 870 hates anything Federal. No rhyme or reason, just a bunch of manufacturing tolerances getting together at the worst time and place.
My .44 Marlin chokes on CCI Blazer rounds. No reason why, it just hates'em. Watch a guy's 1911 spit, sputter and spew last night with Wolf ammo. Just enough of the tolerances on the tight side to cause the 1911 to malf.
That's why we test ammo before relying on it for hunting or HD.
