357 Case Head Separation

[220]

Just looking at saami chamber and cartridge specs for 357 and did not realize head space was so generous on 357.
Chamber rim thickness is 0.060 + 0.010 giving maximum permissible 0.070, Maximum cartridge rim thickness is 0.060 - 0.011.
In effect with a minimum sized case in a max chamber you could have 0.021 and still be within spec.

22 hornet is notorious for case head separations even with guns and ammo within spec, runs similar pressure and head spaces on the rim like 357. Maximum head space with it is 0.018. I know a lot of hornet owners will only use specific brands of case with the best rim thickness to suit their chambers.

Given your guns have checked out within spec for headspace I would be taking some rim thickness measurements on the brass to see if it is undersize. With a rimmed cartridge it is impossible to change the headspace by resizing it is entirely dependent on the chamber and brass rim thicknesses. You have eliminated the chamber being oversize so checking the brass is not undersize would be the next step.

Looking at your original measurements your chamber seems within spec, maximum chamber sizes are listed as 0.3809 at the base and 0.3801 at the mouth with + 0.004. so with you biggest fired case measurement at 0.3830 still within tolerance.

Your reloading dies also seem to be within spec, ammo size is given at 0.3790 - 0.006 so a range of 0.3790 to 0.3730. With your resized and loaded ammo all being consistently 0.3775.
Even if one of these was out I would expect longitudinal splits in the case after reloading a number of times as the brass got worked not head separations.

Case rim thickness is the only thing you havent checked

[Bill.68]

How much of that SWC is inside the case compared to their other bullets? That could spike pressure. When Im loading with PP I very frequently check to see how my powder measure is behaving. PP just seems to not dispense as well as alot of other powders do even though it looks as though it would.
That "cannalure" looking ring around that case is in the trash as soon as I see them, its not normal so in my book its not safe. I just loaded some Xtreme bullets this weekend for the first time and they too happened to be for the 357 but I bought the 125gr FP and also followed their load data and used 8.6gr of VVN340 and was impressed. I bought some plated to shoot in my 586 no- so I would have an easier time cleaning bs cast I normally shoot. Im happy with their bullets.