I did just the opposite a few years ago when I had a 30-06 and a 243 with ammo on the shooting bench at the same time. Fortunately for me, I had 243 ammo in the '06 rather than a reversal. When I pulled the trigger, the report and recoil was obviously wrong. The neck and part of the shoulder was gone as I recall and I was pale for a few minutes. The shooting bench was then cleared and I adopted a new shooting practice... nothing on the bench except what is actively being shot.

Ian

picture of a 9mm bullet fired in a 7.62x25mm chamber.

This was done by an someone else in one of my CZ52s.
These are weak pistols that blow up with the slightest overload, so there must have not been and increased pressure spike. He made a 30 cal hole in the target.

He also shot a 7.62x25mm round in a 9mm chamber, and that jammed that gun.

I had a similar expierience a few years ago when a friend of mine and myself were sighting in our rifles after having rescoped them. Mine is CZ 527 in .223 and my friend has a Steyr in .222, so you can guess what happened. I accidentally loaded a.222 cartridge in my .223, fired the rifle and noticed that the sound was different from previous shots. I opened the bolt, as easy as always, took out the empty case, studied it but could not find anything wrong with it until I took a closer look at the bottom. It read .222 REM! The case had been completely fireformed. The rifle showed no damage which was confirmed by the gundealer I bought it from.
Last year I was at a shooting range where somone had fired a .243 in a .308 rifle. When he ejected the case, it had been split. The neck part was gone and had got completely stuck into the throat of the barrel. Later I heard that this man had to replace the barrel because the brass had been completely welded into the barrel material.

I learned to keep my empty cases completely separate per caliber,never load more that one caliber in one session and check every single reloaded cartridge before I put them in the box.

The damage you describe speaks well for the Mauser design..Most I have seen did about what you describe but stayed in one bellowed out piece regardless of the power behind the explosion...

Not so the M-70s that I have seen blow, the fragmented sending chunks in every direction and ended up in serious injury to everyone around them..

Not to degrade the M-70 or the Mausers, both are the finest built, the fault lies in human error in almost every case, and for the most part should never have happened...

All my rifles are either Mauser or M-70 pre 64 and I have never had a gun blow or even damaged, they both have a built in safty factor on pressure, but a mistaken case full of Bullseye is hard to stop!