Colt Python Light strikes/misfires
I have a 1965 vintage colt Python that I inherited from my father. It has been a reliable and fun handgun up to this point. Last night I was using it for a Pin Match and in the course of approx 50 to 60 rds, I had 6 failure to fire. Asking around, many people thought that it might be the CCI 500 primers I was using. I suspect that it may be a weak mainspring, it is 45 years old after all. I've never had any problems firing single action, but using it for pins, I was mostly firing double action.
The only other issue I can think might be that I didn't seat the primers all the way. I can't really rule that out. The misfired rds had noticeably shallower dimples in the primers. They did fire when I ran them again.
Numrich arms has no mainsprings in inventory. I called Colt, and they referred me to Jack First Distributors. I was going to call them a bit later.
Any other sourcing out there?
Any other recommendations as to the cause? (I will get the mainspring changed regardless, it's led a long happy life.)
Thanks in advance.