It could be the bolt and spring in the new barrel. It should have a two-piece split bolt, if not then get them from T/C and install them in the old barrel. This is the usual reason a Contender will not open, but I am confused that the problem is intermittent. When I mount a barrel with the old bolt it never opens without removing the barrel pin and trigger guard.....
BTW, I know exactly how many barrels I have for my Contenders......
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