Here's something worth a gander: ever heard of Gyrojet pistols? If you like guns, you probably have. I even know a guy who has one. He owns a gun store, and he's kind enough to keep it in one of the display cases in the shop so those of us less fortunate can gawk.
The Gyrojet, you see, is a rocket gun. Seriously: it shoots solid-fuel rockets. The idea was that it would shoot with tremendous effect and little recoil, because the projectile does the bulk of its acceleration while it's whistling downrange, rather than in the chamber of the gun that's in your hand. This also meant the firing chamber didn't have to be as robust, so the gun could be made very light.
It was a real space-age idea. Literally, as the gun was developed in the sixties. Didn't work -- or sell -- as well as the makers hoped. The solid-rocket projectile's continuing acceleration meant, curiously, that the gun did more damage as the range increased, and it was much less effective as a close-quarters weapon. This was bad, because the Gyrojet was not very accurate. Also, the ammunition had a high failure rate, which is annoying on the range and more so if you're in a position to bet your life on it.
Anyway, some fellow is trying to make a new Gyrojet-type gun, and he's been good enough to share his fascination on his web site, which has several Gyrojet articles, including a ballistics test. My favorite period article is the circa-1965 Gun World, which takes it as unsurprising that before being let into the Gyrojet sanctum sanctorum, the correspondent is asked (politely) if he's a Communist. But I give points for the interview with a cop who reminisces about going out onto Lake Michigan and experimenting with weaponry:
. . . once took my Gyrojet out there, [serial] number 67, and the scuba gear. I jumped off of the police boat and went down about, I don’t know, five or ten feet, and I shot the Gyrojet underwater. It was really, really neat. The bullet went out but it left a spiral trace of bubbles from the four rocket nozzles. As the rounds got farther out, I imagine about five or ten feet, but this has been a long time, the bubbles expanded. When I looked where the round had been, and I have no idea how far it went but probably not too far after the burn out, the bubbles kind of expanded. It was kind of like looking down the big end of a megaphone. That’s the best way I can describe it. As they were expanding, they were also deforming. The bubbles were trying to float up. I can’t describe it better than that, but boy was it neat.
Also worthy of note: a blog post on a trip to a 1000-yard shoot. Fun stuff, and the custom rifles are absolutely beautiful.