It can happen to shotguns. Ever heard of a 12/20 burst? Someone mixes the ammo and loads a 20 along with the 12s. The 20 slips into the barrel and the following 12 blows the gun. It can also happen with slugs, mud and wasp nests.
I am guessing obstruction from the way the barrel and slide look. No bulge at the split so it is a hard call. It looks like the slide did not have time to travel so it was pretty sudden. The slide and frame contained it so there was no major shrapnel flying as there would have been on a revolver.
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