New toys were acquired! A chronometer. Backstory - Big Gun rules require to fire up to a maximum momentum of 2" through DOW Styrofoam; which isn't easy to find any more. Our club has some sitting around, so I thought I would try to convert to FPS. @Kotori87 shared some WWCC data a while ago, so I was curious to see how it would compare. His data said 7/32” should be up-to 185 fps. Setup - Filled up the bottle and the cannons magazine. Measured 12” from barrel tip to styrofoam. Tweaked the gun until I consistently/repeatedly was just breaching the back side of the foam. Changed NOTHING except swapping in the chronograph. Results: 180 FPS - The shell consistently passed through the foam. 150 FPS - The shell consistently penetrated about a 1-3/4” of foam. 165 FPS - The shell consistently breached the back of the foam without passing through. So pretty darn close! I’d consider the numbers equivalent, when you consider the variations of styrofoam throughout the years and distance between clubs. Of course, I also found my gun's maximum until it started double firing. I ran a full magazine through it: Min 194 FPS Max 215 FPS Average 204 FPS I'd say not bad as a baseline for a 7/32" cannon. Reading back through Kotori's observations about volume vs flow rate, which completely matches my observations, I'll be tweaking a new cannon variant with higher internal volumes and retesting.
Note, the numbers I have are from a very, very old copy of a WWCC rulebook that I do not have anymore. I did not determine the numbers myself, nor do I know how scientifically they were determined. What I do know is that the chart I have 1) meets ANSI safety glasses testing, so is safe for all properly rated safety glasses, and 2) results in fairly reliable penetration of heavy armor at close range under good conditions, but still results in bounces at long range or at bad angles. In short, a chronograph and velocity chart seems to be a more consistent way to ensure cannon performance meets the intent of the Big Gun ruleset.
Sorry! I didn’t mean it to sound like I was arguing with your data! I’ll edit my post! I actually thought it was close enough to consider it as supporting information. Especially when you consider the years and distance. Yes, I think a chronograph is a much better solution these days. Easier to find locally too!
