This incident happened 25 + years ago and there was no way for MY ammo to have been more than 3 years old. It was most certainly the RCBS case lube as I had just started lubing inside the necks because of the irritable expander ball squeek as I retracted the case out of the die.
And back in those days I was pushing the velocity to the point I wouldn't use my new Hornady book or the Spear books I used the older manual that gave me loads with more velocity, and as I was young and more inexperenced i was having very short case life when setting dies for my Ruger 77R with excess head space. I started to neck size to save on cases but that incident made me open my eyes to head spacing when the primer was blown completly out of the 1st 1/2 of the case.
I use Lee case lube for years now and do not always tumble my brass, and actually I tumble before resizing now because of the media in the flash hole issue.
I havn't checked cartridges for stuck bullets for a long time now but I don't seem to keep many loaded rounds in storage for some reason, oh ya, its something to do with Grandson's
I have seen old pre 1898 handguns that have bulged cylinders and even blown cylinders after the owners fired period ammunition in them. Then the old "Black Powder gets more powerful with age" story's start to come out.
I believe that in many of those incidents your discription of bullet to case fusing is spot on.