I was at the range this afternoon with my SW99 .40 cal. I had put about 17 rounds of 165-grain Federal Hydra-Shok JHP through when I got a nasty surprise.
I'll try to describe what I think happened, perhaps people can help figure out possible causes.
The instant I squeezed off the round I thought for sure my barrel blew up. The tip of my trigger-finger back to the start of the webbing between my thumb hurt like hell. It seems as if the blast exited through the space around the trigger, rather than chasing out the muzzle-end.
At this point there was no barrel obstruction. An unfired round jammed/locked the slide (though the slide was much further forward than in a typical jam), and the round below it managed to jam the mag.
I've put a few thousand rounds through it with only one jam (that I know was due to limp-wristing). I don't usually shoot the more expensive carry-ammo at the range, though I work enough in to be comfortable with it.
*Previous round didn't clear muzzle, obstructed barrel causing next round to cause "explosion"?
*Issue with grain? Ammo?
*Bad magazine didn't allow round to enter chamber clearly?
After I cleared/inspected, I put another 75 rounds through without a single issue.