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!
I'm glad to see people other than me showing interest in advancing Big Gun technology. The old foam method was not particularly reliable, since previous test shots would damage the foam and give widely variable results. More than that, making cannons more available and otherwise advancing the hobby is hugely important. I haven't had nearly the time I want to play with boats, and what time I do get is mostly spent on developing Fast Gun stuff.
@JustinScott is there any chance of you doing similar tests for other calibers? I think it would be awesome if we could all entirely move away from foam.
I absolutely will do for my cannons as I add other calibers. For our next battle we’ll (probably) do some 1/4” Indiana gun tests as well. For this past weekend’s battle I had Tiger’s guns set as posted, and it sure looked like the existing indianas are hotter. That said, who knows the last time they were calibrated. For example, I was punching holes in Bismarck, but she was tearing gashes in me. Admittedly, she has much heavier armor, and it probably SHOULD work out exactly like it did.
7/32” cannon test - upgraded the magazine to a coil-based design for better feeding. Initially the coil alone seemed to max out at 150FPS. I added an accumulator, and got the performance back to baseline, and arguably beyond. The cannon seems reliable at the 200-210FPS range. I was able to get it up to 230FPS, but couldn’t it get back there after I was greedy and tweaked it beyond.
would I be correct in assuming from the sound that there is a delay between trigger pull and bang? How much does this affect accuracy and combat effectiveness?
Good ears! TLDR - The max 200+FPS test does take more time to build pressure compared to battle pressure. At 165FPS, I did not notice a lag at July’s battle. Conjecture- I see this is a limitation of the air tube. I’m using flexible/tiny 1/16” tube for easy rotation. I just don’t get high flow rate into the cannon. I could bump the cannon to higher flow tubes at some point, but today it seems like a bench test problem only. Now that I have said that, I guarantee it’ll be the next thing that frustrates me on the lake.
