SpudFiles

for my next cannon i wanna make a piston because i haven't done that yet. is there much of a difference between co-axial and over-under?

well that is the difference,one has a chamber under the barrel the other the barrel is in the chmaber,a over-under would get more power then a co-ax of the same size as the barrel takes up the chmabers volume so you just make the chamber longer.

so, power wise, it just depends on your dimensions, there's no real stand-out performance difference between a typical co-axial and an over/under?

Well I would think that a Co-axle would preform better that a piston valve if the dimensions were correct, but then again the supah is a over-under style pistion (chamber sealing) valve.

It realy depends on the size of your chamber, size of your barrel, weight of the piston, air tightness of pistion, PSi your using.

Just make what ever feels best for you because it is ultimatly about the specifitaction of the gun you wanna make

From what i read in here i would have to agree with Infernal Maveric, the co-axle delivers a straight push of air, with the over and under the air has to push around corners, slowing down the reaction time, i beleave only by milla seconds, ask Boilingleadbath, he's the math wiz!