[Enosh]

Looks like a S&W N frame.

.357 is my guess.

[Notoriously Conservative]

Wonder if the guy shooting was hurt.

[Tijeras_Slim]

The N-frame .357’s with some exceptions use a thinner barrel. This is likely a 629 or 657 (.44 and .41 Mag) given the size of the rounds in the first picture.

I knew a guy who would stuff as much WW296 in the .44 Mag as could be done and produce giant fireballs. No thanks.

[Dubh_Ghlase]

S&W Model 686, .357 mag. I own one of these. Great gun, and never known of such an incident with one.

My take on the failure is that someone overloaded the charges and there was a failure (slow burn?) on the first shot. When cycling to the next chamber, the first blew while in mid-cycle, and cascaded to the adjoining chambers.

I have never seen a failure like this, and I hope the owner/shooter gives up what they were doing so the rest of us can learn and avoid such a failure...