Thanks for the info on the gun sleeves Bruce, I was not aware of that either.
My 0-frame 20 started doubling on me a few months ago. When I pulled the right trigger the left would also fire, but not the other way around. It happened twice within one box of shells and I switched over to firing the left barrel first to make it through the day without further problems. These were standard 7/8 oz. promo loads. I don't have a trigger scale either, but a stockmaker friend of mine does and we measured them at around 4 lbs. Rt., and 1.5 lbs. Lt. I'm not experienced with sear angles enough to fool with reshaping them, so I disassembled the gun and let him do the stoning, then I would reassemble and re-measure. He went very slow and for the first 5 or 6 tries nothing changed, but then we started to see the pull increase. About two more tries and we had it up to around 4-1/2 lbs. and called it good. No problems since, and the triggers feel great. I have often wondered why the left sear would wear before the right, since it typically gets used less, but there it was. As I'm sure you know, it is common practice to have the left trigger with 1/2 to 1 lb. greater pull than the right to help prevent doubling. The final pulls we arrived at were listed in notes my friend had taken while attending a gunsmithing seminar put on by English smith Jack Rowe.
You could probably get a ballpark idea of the trigger pulls with a fish scale and a string tied to the trigger, but you'd have to watch very closely at the time of the break to know where it happened. A proper trigger scale will mark the point of the break with a "bug", like on your aircraft instruments.
Jim
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