Originally Posted by
Lakey
One of the problems with the underlever system that BSA used was the constant threat of injury from accidentally firing the gun, with the underlever in the open position. This would result in the underlever smashing up against the barrel, with the possibility of serious injury to hands and fingers. This was even more likely if the trigger adjusting screw was set a bit on the light side.
Lincoln Jeffries developed the system of a double sear, which was articulated with the trigger. these two sear hooks engaged into two notches on the piston rod. The idea being that a definite hard pull was required to fire the gun, instead of a light pressure as was often the case previously.
The patent was accepted in October 1911, and was first fitted to production guns around March 1913, however not all guns were fitted with the new trigger. It proved to be a failure in practice, so in order to use up all the parts that had been made, they riveted the separate parts together, so that the unit reverted to a single pull trigger .
First fitted in the 65,000 serial number range, production finished in late 1914, so it is a relatively rare trigger variation
All information from John Knibb's book " Lincoln Jeffries and BSA Air Rifles - a history of innovation" -------- Great read for all enthusiasts
Regards
Lakey