Single triggers have been around since the late 1800s. Parker first used the cranky Lefler patented SST. Pages 140-142 of The Parker Story covers this improvement in gun design very well. The Parker catalog of 1920 shows a single trigger used in their SBT trap gun. The first catalog showing the SST as an option is in 1926 according to the Muderlak - Parker Guns-The Old Reliable (page 70).
There were some car dealers that never believed the differential drive train improvement on 1900s era cars would supplant the cog and link drive chains used on earlier cars. Some of us still insist on fishing with bamboo fly rods. OMG - some people still shoot 140 year old SxS guns with double triggers. There are even some people who actually drink Scotch that's 18 years old. Go figure!
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