by tpark » 29 Dec 2016 21:33
If locks have been outside for a while, they can get grungy and the core might be a tight fit. If a core doesn't go in too easily, I grab another core and try that. Sometimes the lock is a bit deformed from being beaten on at sometime while in service. Sometimes (in the case of BEST locks) the shackle retaining plug is slightly twisted out of position. But, as others in this thread have hinted, there's additional information you could provide that could make diagnosis of the issue much easier.
--Ted