Barrels will not lock down and release top lever

[BRDHNTR]

Took a 20 ga trojan for skeet today at my club in plymouth. Was shooting reloads, some of which the crimping was not tight and some shells had not been fully re-sized during reloading process. Anyway, one shell was very swelled and gun would not close except under great pressure from me. After shooting, tried to reload and top lever would not lock down. Barrels would go back on ok, and would seemingly close tight as usual but top lever would not , will not release to locked position. Inspected inside of frame and saw no lead deposits. Barrels seem to seat tight but top lever will not release. Any thoughts? Is there a spring i may have broken by forcing the barrels to close on the shells as noted above?