A very small batch of special target model pistols was made at the very end of Astra 400 production in 1945. They were fitted with Patridge front sights and adjustable revolver-style square-notch rear sights, much improved over the stock Astra 400 sights. In addition, they were fitted with a special single-set trigger system in which the sear engagement was dramatically lightened to give a very short and light press. However, the sear engagement was so light as to risk doubling under recoil, so a hammer catch was added. Before each shot, a button on the back of the frame had to be pressed to release the hammer onto the sear.
A handful of ex-service Astra 400s were also retrofitted to this pattern in the late 1950s; these can be identified by their salt blue finish instead of the regular rust bluing.
For more information on these and other Astra pistols, I highly recommend Leonardo Antaris’ book “Astra Pistols and Selected Competitors“.