We can calculate the energy of a paintball at 300 fps. In the case of 3.2g and 300fps, we get 13.37 joules, which is 9.86 ft-lbs.
In Germany, I believe they regulate the paintball gun so that it cannot shoot a paintball that has more than 7.5 joules of energy. Taking that with the weight, we have 7.5 = 1/2 (.0032)v2. Completing that equation gives us a velocity of 68.57 m/s, which is just under 225 ft/s
The test of "shoot it and see what seems reasonable" is adequate in my opinion, since there's been no calls for reducing the limit under 300 fps. Many fields voluntarily choose to use a slower limit, but nobody considers up to 300 fps dangerous compared to 285 fps or slower.
This post has been edited by andrewthewookie: 08 October 2012 - 01:47 PM