Well, in all honesty, they're are a bunch of us who could give you a swell WAG (Military acronymm = Wild A$$ guess). All would be just that. A Guess. I personally would have to see the gun cycle to get specific. But (WAG coming) my first look would be at the firing pin hole in the recoil shield to see if it's "puckered" and sporting burrs that catch the primer as it backs out of the case upon firing.
The problem is going to be at, or down stream from the firing pin hole. the frame may also be out of square and the head space decreases at the bottom of the recoil shield.
If your not some familiar with the function of a SA type handgun, you have another visit to a gunsmith in your future.
What type and brand of strap cutter do you use? A pistol grip draw guage cutter or wooden strap cutter? I am getting these names from ebay so forgive me if they are not the proper terms. Do they use the same type of general razor blade?
I cannot afford nor do I do enough work to justify an expensive machine, so I am looking for one of these hand ones.