As for Spanish single triggers, O'Connor wrote of having the single trigger on his 28-gauge Eusebio Arrizaga replaced with a Miller.

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Researcher posted a long list of single trigger patents for which I'm looking.

If I did, I haven't been able to find it in my saved posts Word document. Maybe Larry Schuknecht?

My first single trigger gun was a CE-Grade Ansley H. Fox I picked up in a pawn shop on Hotel Street when CVS 14 Ticonderoga was in port at Pearl in 1971. I stripped the finish off the wood and recut the checkering then gave it to Bill English the best gunsmith in Seattle at the time to epoxy a crack in the wood, finish the wood, fit a new recoil pad and blue the barrels. When I got it back from Bill, he mentioned that if one wanted an American double with a single trigger the only one to get was a Model 21. But, that Fox-Kautzky, even with all that work on the gun, functioned flawlessly for two seasons and a lot of limits of Doves in Southern California. Not too long after I arrived in the DC area in 1975, it flowed down the river of commerce to the Hartmann brothers.