2. On the Buck Rogers TV show - Buck is captured by some space bad guys who have found a cache of 20 th century crap to them. In it, there is a Browning M1919 machine gun. He casually picks it up and ...
I remember that episode. The Future eggheads thought it was a communications device. Buck managed to communicate his intentions very well with a couple of long bursts of .30.
Guess you could call it a "burst transmission" device.
There are legal full auto airguns that can cut a 55 gallon drum in half. Easy to build from the schematics I've seen. These require an airtank in a back pack for extended firing, but I suspect much smaller tanks could be used.
I figure the deisel piston rifle will be better developed in the future. The Germans used these after WW2 for small game hunting. They converted regular spring piston air rifles with a device to squirt vaporized wood alcohol into the cylinder before firing. They got power levels between the .22 LR and .22 WMR using cast bullets of the apropriate weight.