I have seen it happen twice and I know of one occasion with a club member.
The two I witnessed both had under charged ammo left in the magazine, both were from objects blocking the powder measure (one was the little foam seal from the top of the powder bottle, I think the other was due to bridging in the Dillon powder measure tube which is often solved with polishing).
The last one was a member trying to make reduced loads to subsonic by just reducing the powder. It got to a point where the charge just exploded.
All these were on AR style rifles and with the exception of magazines and bolt groups there was no other major damage. The brass flowed in all instances and the bolt had to be eased out of two (the other actually stripped the carrier and half cycled the action before the pressure left the rifle via the magazine and the eject port).
With something like a 223 there is more danger from under filling than over filling, it is hard to get enough powder of a suitable type in the case to cause a problem but a half charge is dangerous.
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