Years ago I was deer hunting In below freezing temps, maybe in the teens. I slept in the back of my pickup ( it had a cap) with a foam mattress and inside a good sleeping bag. My rifle was inside also but I didn’t have any heater.
The next morning I had a nice shot lined up for a doe and pulled the cock back, took aim, pulled the trigger and in the corner of my eye saw the cock slowly, ever-so slowly drop and rest against the frizzen.
Turns out the main spring cracked and broke.
I don’t know if it was the very cold conditions or that it was one of those early cast mainsprings on the L&R lock, or a combination of both, but that was it for that hunt. (Now I have spare mainsprings).