"Cartridge form" .........

is a good way to characterize it. Here's the back end showing the thumb button used to close the exhaust valve. Also visible are the threads that secure the whole assembly (5.7 in. long) into the upper tube.

 

[IMG][/IMG]

 

Here's the front, the end of the exhaust valve being visible. With the valve closed and the barrel locked into place, the conical tip enters the pellet skirt. No wasted space.

 

[IMG][/IMG]

 

                                                                                        Ron