603,
OK, it's not the ammo then. I doubt that new die will do anything if factory ammo is splitting. And if the bullets are not being pinched (neck length fine) then it's looking like too much clearance around the shoulder neck area. And/or the bullet is jamming in the lands because of the throat.
Factory ammo, multiple brands of cases, mild load, you obviously know how to hand-load - got to be the chamber.
Here's a thought, that chamber might still be more than .300 if when the split occurs the gas escapes, pressure equalizes and drops inside/outside, and the case stops expanding. I read that in some large chambered old guns hand-loaders sometimes use two lots of firings to fully fire-form their cases, by using mild loads. So one mild firing expands it half the way, and the second fully fire forms it. If they used a full single load from the start it would split the case. Also, sloppy machining of chambers in cheap barrels is to be almost expected. It makes sense it's more likely a simple reason rather than something more exotic like a die from a reputable manufacturer ('Occam's razor').
OK, it's not the ammo then. I doubt that new die will do anything if factory ammo is splitting. And if the bullets are not being pinched (neck length fine) then it's looking like too much clearance around the shoulder neck area. And/or the bullet is jamming in the lands because of the throat.
Factory ammo, multiple brands of cases, mild load, you obviously know how to hand-load - got to be the chamber.
Here's a thought, that chamber might still be more than .300 if when the split occurs the gas escapes, pressure equalizes and drops inside/outside, and the case stops expanding. I read that in some large chambered old guns hand-loaders sometimes use two lots of firings to fully fire-form their cases, by using mild loads. So one mild firing expands it half the way, and the second fully fire forms it. If they used a full single load from the start it would split the case. Also, sloppy machining of chambers in cheap barrels is to be almost expected. It makes sense it's more likely a simple reason rather than something more exotic like a die from a reputable manufacturer ('Occam's razor').