So I'm not sure if this has been discussed yet or not.. but is it really fair to judge both forms of paint at their 300fps marks?
If you hold your 300fps to be constant in testing, yes a larger (read: heavier) ball will always break better/fly further. It simply has more mass, and with your constant velocity, will always break at further distances by having more kinetic energy from the start. If you extrapolate this to its logical conclusion, the day someone comes out with 90 caliber paint, they will, with your own tests, prove that 90 caliber is "better" than 68 caliber. (new form of "pro" paint anyone?) However, I think I can predict the future here: you will argue that 90caliber paintball is "unsafe" on account of it being too heavy for that speed. (Reballs are already treated this way, required to shoot at a lower fps due to its higher mass)
Therefore, I propose that in order for 50caliber to really have a legitimate chance, you need to hold a different part of the equation constant: the kinetic energy. Just like you would hold 90 caliber to this particular parameter.
Its to my understanding that (and this is completely unfounded) the ASTM standards are designed to withstand an impact with a certain kinetic energy behind it? If this is true, then according to my math, 50cal paintballs should be able to be fired at 485fps with no ill effects on the target. You'll have the exact same amount of kinetic energy behind it.
So what exactly prevents us from firing smaller balls at more than 300fps? Why was it 300 from the start, instead of perhaps, 200fps.
I think the idea behind 68caliber and 300fps are linked by account of precedent. 300 fps is in place because of 68 caliber, and 300fps will deem that 68 caliber remains king.
It is not until we use the idea that Kinetic Energy should be the reigning factor that we can even consider other ball formats.
Work:
http://www.mcarterbrown.com/gallery/...68_ke_vs_v.jpg