If you had a firing pin replaced, that may be the problem. Is it the pin that was replaced that is dragging?

I have run into this before. I had my gunsmith make up new pins for a cheap spanish double and on those guns the hammers do not rebound, so when fired they stick out. The new pins were too long and the gun barely wanted to open after fired. I just gradually took material off the end of the pins until it would open without trouble, but still be able to detonate the primer.

B.Dudley