Issue with Pulling Hammer

[culperring]

On one my Mini's (it is a LR), I have been having some issues with the pulling the hammer back.  Today it was particularly bad.  Prior to today, there were times when it was a bit harder to pull the hammer back but it would (my other Mini works fine).  However today, I would shoot 2-3 rounds and then I could not pull the hammer back to shoot.  I would take the cylinder out and extract the rounds and then put back in the unfired ones.

I have read that 9mm revolvers have some issues with bullet migration, do 22 LR have a similar issue? 

Or might the already fired rounds be catching (where the hammer hit them) as the cylinder turns? 

Or might it be the internals? 

Thank you.  Mini's are so much fun to shoot!