model 100
The Win model 100's are grand old rifles. Though I never owned one, I've handled quite a few and been tempted many a time, always felt they swung and pointed nicely. But I never saw many afield, and I sure don't see any these days. The Remington autoloader's from the 740 on up are still as common as flies though.
You fail to mention for what caliber your M100 is chambered?
Finally, back in the day, there was a major recall on the M100 regards the firing mechs. I don't recall the specifics, but seems as if the rifles of a certain vintage could be prone to "doubling". I sure could be wrong about that.....certain there was a recall, not sure of the exact nature. I knew a fella that hunted one frequently remarked that his would double, and he was not aware of the recall, .....but of an age where he should have.........no internet in those days of course.
With Winchester as we knew it largely defunct, I dunno about rework's or inspections on a M100 nowaday......but a good 'smith in his 60's or so ought to be familiar with the issue.
Heck, we may hear from others regards this soon.