My daughter shoots Super Colibri's in hers cuz she can't stand the noise level of standard velocity .22's. They have a standard length .22LR casing, but the bullet is shorter. After she shoots a few, I can't get a standard .22LR to chamber due to fowling deep in the chamber. The same thing happens when she uses my single shot Savage. Give the chamber a good brushing out, might just be some fowling or a fleck of lead in there.