[Slamfire]

You were firing old surplus ammunition, ammunition that was discarded as unsafe by the Yugoslavians and sold to ignorant Americans, and you were firing it in a 1890’s vintage rifle.

You are lucky the ammunition was not so overpressure to blow up that old plain carbon steel receiver.

Also, that mainspring on that 1888, it probably dates to 1888. A 125 old mainspring needs to be replaced.