been shooting 1911s for 50 yrs.,never had this to happen before.
firing pin stop came down and caused a jam---happened twice today at the range.
SUGGESTIONS?

What brand of 1911?
Someone on here had that problem with a Para.

Check for firing pin wear, and make sure the stop isn't worn or broken.

Also check the spring. If its broken or binding, that might make it happen.

I don't know if a worn spring would do it, or not.

You mean the firing pin stop on the back of the slide?  Not the series 80 firing pin safety?

If it's the slide stop at the rear of the slide, I would guess that either the slot is loosening, or the stop itself is compressing, thus loosening.   If that's the case, get a replacement firing pin stop.  

The firing pin has to go back and forth fast enough to help retain the stop.
If yours is an original design, with no firing pin safety, I'd look for a firing pin spring, besides the cheapest part, it's a good spare part to have around.
Also compare the lengths of the new & old one.
After cleaning and reassembly, push firing pin in & out to check for binding.
At least that's where I would start.
Should be good for another 50 years.