Patent filed in 1937 by Poyner Jones for a pull-release trigger with an interesting commentary suggesting release triggers were commonly used at that time -
As is well known to those skilled in the art, within recent years there have been a number of trigger mechanisms wherein the gun is fired by releasing the trigger rather than by pulling the trigger. This trigger mechanism is known as a release trigger. The real purpose of the release trigger is to try to overcome the tendency in the shooter to flinch, which flinching is due to nerves and also to the fact that in applying pressure to the trigger, anywheres from three and one-half to seven pounds, the muscles become taut and the shooter is unable to hold the gun at the desired point of position or even pull the trigger.
It is a well-known fact, however, that where a release trigger is used, the loosening of the muscles, that is, on the releasing of the trigger, has a great tendency to overcome flinching.
Release triggers have heretofore been mostly applied to trap guns, that is, guns which are used at the traps, rather than to field guns, as to change over entailed a dismantling of the mechanism.