Big Bob,
Yours sounds like the most logical explanation of what a loose primer causes.
When I logically thought about it, the cartridge is locked into the barrel, and the bolt firmly butted up right behind it. So I couldn't quite understand how a bolt is going to bind up, or a primer back out, or such other radical event take place. As you say, hot gasses cutting the bolt and escaping the chamber possibly into your face, makes much more sence to me.
An excessive high pressure "hot" load is going to cause trouble with any kind of a primer, loose or otherwise. (ie: stiff bolt, split case, flattened primer, etc) I know not to do this, as I've been reloading periodically over 30 years, and am well aware of the signs. But I don't think I've experienced so many loose pockets through the years with other calibers as I am with my new 223 loadings. (first time I'm loading 223)
My experience that I am referring to is with new UMC fired cartridges, that I have reloaded only once, and below the max loading I may add. It seemed to me the primers were slipping into the pocket fairly easy in these only once fired shells. Factory Winchester cartridges (Israel maunfacture)that are fired once, look to have flatter looking primers then the Remington brass. This tells me that Winchester cartridges are loaded to higher pressures then the Remington stuff. So as I get ready to reload the Winchester brass for the first time, I was concerned if the pockets will feel even worse then the Remington shells.
Anyway, I think the "loose" primer pockets I'm reporting may not be as loose as I seemed to think they were. I suppose when one is really "loose" .... I'll know it!
As far as wearing glasses.... no I don't wear them except for the first round or two of a max or near max loading that I'm not familiar with. Of the thousands of rounds I've fired over my lifetime, I've had one primer in a 22-250 cartridge blow gasses into my face and my eye about 30 years ago. Luckilly I suffered no injury except a red eye. It was a factory cartridge too!
I single load and weigh all my cartridges, and check the powder level in all 50 cases in the tray before seating the bullet. I think if you don't double load a case, or putting the wrong cartridge in the chamber, you've got slim chances of harm. (yea, blowing up a gun will require safety glasses) So I live life dangerously.
BTW, I'm in South Texas. The biggest threat we have to our safety here at our firing range is the lack of knowledge and the disregard for firearms safety. I have been at the range on numerous occassions when people who don't speak our language and look like they are handling a gun for the first time will take a shot or two out of the 12 shots in the magazine, and pass the pistol around to the next guy with the hammer still cocked and ready.
That sought of thing (and other stupidity) will get me long before another factory Remington 22-250 ever reoccures....and get me real BAD!