I've seen lots of both failures. The damndest things will cause trouble with them, as well. My Father had a spiffy pachmayer pad installed on his Beretta Silver Snipe, circa mid 1960s. The single trigger, an inertia style unit, suddenly became unreliable, with any load. Dad proceeded to discover that most automatic shotguns (Notable exception being A5s, in our experience, they typically seem to go off when the trigger is pulled) really, aren't automatic, in the next two or three decades, during which time, the installed pad on the little used Beretta, became a lot harder. Bingo. The trigger now works, well, again.
I did strip and clean the Beretta, several years past, and discovered that some Italian gun worker thought it needed good sized gobs of grease applied, which had fossilized in the time since it was built. Double triggers are less sensitive to this, sadly, not unusual treatment, in my experience.
I've come to view single triggers as just so much bling installed on a gun, a heavier, even more unreliable form of bling in the case of selective single triggers. Much like the automatic bail that was installed on Mitchell spinning reels in the 1960s, which made it possible for handicapped individuals to cast, they actually are a handicap for able bodied individuals in use. You have complicated, and, typically, lost the ability to select the better choke from your double gun, for the presented shot with either form of single trigger. Mr. McIntosh got this one EXACTLY right.
If you hand is cold (the most common excuse for a single trigger) handwarmers are cheaper, and much more reliable.
Best,
Ted
