How about a big rock you could throw? Then you could throw at things coming from the side, in front and behind! =) The ammunition isn't 5 bucks a pop like my last suggestion and the launching mechanism won't put you back 8 grand, nor knock you off your bike =) I would love to see a sport arise from this, like painball road races, where the paintball guns just point ahead and 100 mile races of swerving side to side to avoid the paintballs from behind. Every hit could be a point deduction at the end =) It would be so easy too, the only difficulty would be mounting the paintball gun so that it wouldn't cause additional injuries when the rider crashes, so a bar mount would be difficult. It would be so studly to have a trigger under your brake lever =) With all of the fourth of july celebrations over you could buy a lot of big rockets on sale and buy a pvc pipe slap some grips on it and a firing mechanism, and you have a rocket launcher.... this has some merit too, it would be nice to ride with on your back, if you could make a good enough sling, it would take one motion to grasp the grip over your shoulder and bring it onto your shoulder and onto bear with your target. Your aerodynamics wouldn't be sacrificed with the launcher in your drag shadow =) if you made the launcher furry, it would benefit you to carry. I have had some fun with a flare gun while riding =) Those are pretty cheap, and would scare any attacker pretty badly, you could hurt someone if necessary, and if you were injured out in the middle of nowhere, you could signal someone =) As with frame material there seems to be strengths and weaknesses with all of these designs. The trebuchet is a bit dated and ill suited for cycling, the mangonel is much better, but still a little too complex for the recreational cyclo-destructivist. The ball bearing launcher would be an easy fix, the compressed air could be kept in bottle sized tanks on your frame. The Barrett has a lot of strength(s) but, has too many drawbacks in price and size (60 inches, 40lbs), with a 22 foot/pound recoil, you could easily lose control of the bike, the necessity for hearing and eye protection would also hider riding ability. The sex appeal from a macho point of view is high, though, actuall sex appeal is questionable =) Flare gun seems to be an almost legal choice, as long as it looks reasonable difficult to get out in a hurry, and you are extremely good at lying. Rocks are prevolent and versatile, but potentially weighty, there is nothing to make your jersey look more silly (in some cases) than a heavy weight in the rear pockets. Rocket launcher is fun but, the design is much more difficult when a more in depth look is taken. Paintball gun like the ball bearing gun is great. the only design would be in storing it on your bike, and possibly a trigger on your bars, or a bite trigger =) I don't know why the rifle or pistol industry hasn;t gone with bite triggers, I can bite awfully quickly and it would free up a hand for better position. Do any industries use bite triggers? Anyway, if they don't I have dibs on the idea.. along with a few more great ones for bike locks!!! =) I can't share them they are too good! =) anyway, these are the major designs laid out so far, painball seems a good direction to move towards, less dangerous, less threatening and more legal, cheaper, readily constructed, and cheap ammo. Your CO2 cartridges could be swapped for a Microflate cartridge in a bind as well =)
-Jacob