That’s a nice example of the Deluxe model with the adjustable sights and shaped grips. The basic model has fixed sights and slab grips. They are a very neat and quite simple design.

The cylinder and piston are oval but the spring isn’t, it’s a conventional coil spring.

The biggest problem with these is that the piston seals have a tendency to disintegrate and whilst factory replacements can be found, they are scarce. I have had some success in making leather replacements which seem to work as well as, and sometimes better than, the factory spec. I believe they were originally meant to generate around 280 fps but can be pushed to a little over 310fps.

As well as the Jumbo, FB Record also made the larger Champion. This uses the same concentric barrel and oval piston combination but with a side lever and magazine fed pellet repeater mechanism.