Took the gun to a top-notch gunsmith, showed them the case and they reaced the same way as folks here - WOW! bad news.
I brought the ammo and the ruptured case.
Of course, they first checked that the barell was stamped .223 - it was.
Then they loaded a round, and the gunsmith immediately said it felt "funny" as the cartrige was "to far down" in the breech, which now that I look at it, it, it does NOT look like any of my other break-action weapons in terms of where the cartrige sites vs. the back of the breech. However, each gun is a little different, and when I loaded it, it actually looked like it was a normal fit, not flush to the back of the breach, but still it seemed to fit cleanly and correctly.
A quick casting determined that someone had modified the barrel to be a 22-250, with a trim-to of 1.902", which is larger than the 223 Remington - 1.750"- a difference of .152".
Unfortunately, the gunsmith neglected to modify the BARREL MARKINGS and as a result, the use of the .223 cartridge resulted in the situation.
Lessons learned:
- Trust no marking
- If it seems "funny" to you, it is! The loading of the .223 wasn't like any other break action I ever used, but I also never used a NEF Handi-Rifle.
-Each gun it a little different, but still, if you have any questions, find someone who knows better than you. I was impatient to try the gun, it's might cost me more than I paid to replace the barrel (I wanted a .223 NOT a 22-250) and repair the firing pin, if that's the case, this gun might be a total loss.
- I've just gotta stop buying used guns. The last used gun a bought before this was an SKS that came via mail order - with NO SERIAL NUMBERS ON IT. Torch cutting that one in the back yard in the pouring rain was unplesant. Now this.