I have obtained a second example of these curious devices, of more recent manufacture with a number of refinements compared to the older original. Here they are side by side, with the newer version below the original one:
The most obvious refinement is a cutout in the breech that allows the projectile to be loaded without having to completely remove the bolt like in the original:
Here are the bolts compared:
Another refinement is at the end of the gas tube, instead of having two fixed power settings like on the original there is a power adjustment screw on the endcap. There is also a thumb safety (seen here in the "fire" position) that can be moved back when the hammer is cocked to prevent it from firing when the trigger is pulled:
The markings on the barrel suggest that unlike the earlier model that was a third party adaptation of a Crosman rifle, this version was actually manufactured by Crosman:
