It is an interlock safety problem, probably related to the locking lugs on your new barrel. Does the barrel have two lugs (split)? If not, get a set from T/C. It could also be a lubricant problem - you should never use oil on the lock work of a Contender. Spray the frame interior with degreaser to remove all oil and gunk, then wipe the outside of the frame with an oily cloth. If you feel you must, use some powdered graphite on the aciton parts - but just a tiny amount.
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