Tuning Winchester 1977 - Super Difficult to Pump

The gun was working as it should. I was really happy with the accuracy, however, one day, after pumping 8 times, I was interrupted, put the safety on and secured the gun. I was not able to get back to it for a day or two. When I pulled the trigger, it sounded different from what I was used to. I went to pump it for another shot and I could barely complete 1 pump.

It will shoot a pellet after one pump but it's nearly impossible to complete the pump without feeling like something is going to break as a result of the physical force required to pump it.

The gun has been stored in a clean, dry area and never dropped or abused - it's only a few months old and it would be a stretch if 200 pellets have been discharged. I have not taken it apart as I am hoping someone with experience could recommend a fix.