You might be talking about a mainspring / hammer spring.
But that is unlikely too on a fairly new SIG that doesn't have half a gazillion rounds through it.
It's an early 1990's pistol of West German origin. I haven't had it that long, so this might be a possibility. I don't have any good idea of how many rounds have been through it, but it looks clean so I suspect it hasn't been that many. No problems with any other ammo I've tried.
Have you cleaned the chamber throughly with a bronze bore brush & solvent, ever??
Have you cleaned the slide & firing pin channel with spray solvent?
It had been exactly 108 rounds since it was last cleaned very thoroughly. I will re-check and take it to the range again this coming weekend. We'll see. Thanks for your ideas! I really appreciate it. And everyone else too!