I've seen this happen too often, a Hunter ends the Season with a loaded ML, it was shot and reloaded, the season ended and he said I'll fire it and clean it. Well the days turn into weeks, the weeks into months. All the while the process of corroision starts to eat away at the inside of the barrel. It's called being LAZY!
Chances are the Barrel is Junk, Im not saying this for sure but chances are it is. Im not a TC shooter so I dont know about getting another, but Bergara makes replacement barrels for TC ML'ers, if they have one for the triumph I'd get a Stainless Steel one. Check them out at bergarabarrels.com or call them at (877-892-7544)
Good Luck to you!
(BP)