Many two-smoke pistons have the ring's end gap pegged so that they pass up and down on a part of the barrel that has no ports in it i.e. solid wall.
if looking down on the piston/barrel top with exhaust pointing away from you, then the rings are often pegged at about 7o'clock and 5o'clock positions on a conventional two stroke setup.
If you fit the piston opposite to this, then the ring ends drop into the exhaust port and snap them when turned over....a fairly common cock-up.
Put a felt pen mark on the piston top to align with the ring pegs and put the barrel on WITHOUT the rings, and gently turn it over to see if the marks line up with the right part of the barrel and miss all the ports.....Bob's your uncle.....hopefully
