the force it hits with is dependent on a lot of stuff, but really you probably dont really want force anyway, Kinetic energy and momentum are better suited for terminal ballistics. and those numbers I have. Well I have small gun numbers and could get them for big gun if needed, or you could its pretty easy to calculate. First for an Ideal Gas gun with a 5 in barrel shooting a .177" steel ball using 150 psi Muzzle Velocity = 105.6 m/s = 346.7 ft/s Assume Steel density of 7.85 g/cc Projectile Mass = 0.000373499 kg Momentum = 0.0395 N*s Kinetic Energy = 2.09 J However thats not realistic since our guns cant shoot that hard in real life, so we shall assume a more realistic muzzle velocity. Muzzle Velocity = 84.53 m/s = 277.34 ft/s (this is still probably 50 ft/s or more over what we battle with but is about the hardest ive seen or heard of one of our guns shooting) Assume Steel density of 7.85 g/cc Projectile Mass = 0.000373499 kg Momentum = 0.0316 N*s Kinetic Energy = 1.33 J And finally at one thats closer to what we actually fight with a battle tweak. Muzzle Velocity = 64.6 m/s = 211.8 ft/s Assume Steel density of 7.85 g/cc Projectile Mass = 0.000373499 kg Momentum = 0.0241 N*s Kinetic Energy = 0.78 J Thats not a whole lot, im sure we could find data for bb guns and or paintball guns and such to compare these values to. EDIT: according to wiki paintballs have about 11 J of Kinetic energy, (dependent on muzzle velocity but as you can see we are about an order of magnitude smaller)
Since you are doing all the math calculate for big gun sizes and pressures. Then there will be no doubt. And many kudos awarded!
Dam, pellets shot from a fast gun ship have nearly no "stopping power" at all. That will help me greatly thanks snipe!
alright but i need more info like size and pressure also i need the effective barrel length. for our boats i measure from the oring and use the max allowed barrel length, well not counting restrictor guns. im not sure what that distance is in big gun since your guns work a bit different id make sure people know you mean bbs and not pellets like the target air gun shooters use. cause from my experiences pellet guns are more dangerous than bb guns and the rounds are better at penetrating stuff since some of them have points and such. well and lead pellets would have different values since lead is a bit denser than steel.
Anecdotally only: I've been hit in the shins by plenty of both, & I know the small ones hurt the worst. JM
pressure is 150psi for big gun size of shot is 1/4" ball bearing (other sizes are available, but 1/4" is the extreme) -> I don't know the weight. barrels are a bit longer than FG... John wanna crack open that ship of yours? I'd say 8" barrel length. ----- Something to note: Big gun uses a huge (like 1/2") apperature and fires all barrels at once, so operating pressure is drastically reduced... basically to zero during the firing process. ----> I think you need muzzle velocity to calc this for big gun. ----> Isn't there a penetration test for big gun cannons? 2" blue foam? Perhaps it would be easier to calc from this?
Ok, Took those numbers and did the ideal gas gun equations for it. 8 inch barrel 0.25" steel ball bearing 150 psi Muzzle Velocity = 112.46 m/s = 368.97 ft/s Assume Steel density of 7.85 g/cc Projectile Mass = 0.00105242 kg Momentum = 0.1184 N*s Kinetic Energy = 6.655 J wowzers thats a heck of a lot more than with the bbs. Ill stick to small gun. [] So if those numbers (barrel length) are right then these numbers are the MAX you could ever see in a perfect world, but just like with the other guns your cannons are not perfect gas guns, due to blow by and the decrease in pressure you mentioned and all that jazz, so in the real world the numbers would be lower. on another note what device are you using that has a 1/2" apperature that takes 150 psi?
id make sure people know you mean bbs and not pellets like the target air gun shooters use. cause from my experiences pellet guns are more dangerous than bb guns and the rounds are better at penetrating stuff since some of them have points and such. well and lead pellets would have different values since lead is a bit denser than steel. [/quote] good point
The velocity of a big gun cannon is lower than a typical fast gun cannon, as they have to pass a penetration test. i.e. nowhere near 370fps. It'd be nice if we could get some input from a big gun captain who knows what his firing pressure is (they run secondary adjustable regulators to drop the 150# down to whatever lower pressure will allow them to pass the foam test)
Allow me to go into a little more detail about how cannons (all model warship cannons) work, and the physics math behind them. At its very base level, the round that a cannon fires is propelled by the pressure differential between the gas behind it and the gas in front of it. That pressure differential determines the force with which the round is pushed. In an O-ring cannon at 150 PSI, at the moment the round slips past the O-ring, the pressure differential is 150 PSI. Do a little unit converting and multiply that by the cross-sectional area of the round (2mm^2 * PI = 12.566 square mm) and you get the initial force applied. That totals out to approximately 12.995 newtons of force applied to the round the instant it slips through the O-ring. In an ideal cannon with zero friction and an infinite supply of 150PSI gas, the shot will be accelerated by that force for 5 inches, and SnipeHunter's initial calculations show the result of this pretty well. However, our cannons are NOT ideal cannons. They do have friction, they have a limited supply of gas, and they have a certain amount of blow-by, AKA pressure that slips past the projectile and slows it down rather than accelerating it. It is possible to calculate some of these elements, but others are not so easy. For example, we can safely assume that the volume between the selector piston and the O-ring is the amount of gas readily available. Sure, additional gas flows in from the air lines leading in, but this is the amount that can flow at full speed and maintain pressure behind the round. Knowing how much gas is in this "accumulator" space, and the dimensions of the barrel, you can calculate how the pressure (and thus, force applied to the shot) will drop as the shot moves down the barrel. Other factors, such as friction and blow-by, are not so easy to add into the equation. Big Gun cannons also add in backspin, which makes the friction and blow-by even harder to predict. All of these add up to reduce the final muzzle velocity of the cannon. I am not a professional gun-maker and I'm certainly not an expert on the physics here, so don't take what I've said for granted. I have tried to predict a cannon's muzzle velocity with math before, but I have never succeeded. I think what I've outlined above explains why, but I make no guarantees.
The AusBG requires that all cannons have no more than 165 fps muzzle velocity. That applies to all cannons, be they 1/4", 7/32", 3/16", or .177". I remember that the WWCC used to have a muzzle-velocity chart in addition to its foam test, and the muzzle velocity for 1/4" was 165 fps, like the AusBG. However, I also remember that the smaller calibers were allowed greater muzzle velocity. I think .177" cannons were allowed 225 fps, though I can't be certain until I check a really old rulebook. I do not remember the velocity allowed for the in-between calibers. Since Tugboat asked, my cruiser's torpedo cannons pass the foam test between 120 and 130 PSI, depending on the weather. That's firing six 1/4" balls, two per barrel, into 2" target foam from one foot away, and not going all the way through. Sometimes the shots just barely bulge the backside, but don't break through, and then I know I'll be hitting really good for that day. I also remember that one particular Prinz Eugen cruiser had to operate its cannons at 40 PSI to pass the foam test. It had monstrously oversized accumulators, and super-long tight tolerance barrels, but even so 40 PSI is a mind-bogglingly low pressure to operate cannons at. Most cannons operate over a wide range of pressures, depending on their accumulator size, gas routing, aperture sizes, and projectile caliber. The average "Indiana" cannon (your classic rotating Big Gun cannon) operates between 100-140 PSI. Other designs have more efficient gas routing, which boosts efficiency and allows lower operating pressures. I remember the infamous Stomper cannon operated at about 65 PSI, and several torpedo cannons operate at 85 PSI. Still others are not capable of failing the test (and reaching the maximum hitting power), even at 150 PSI. When your cannons are at max pressure and still bouncing off the foam without leaving a dent, it's time to get better cannons (and yes, I've seen this before. It was rather amusing).
For the record, Carl, my cannons ARE ideal, hand-forged from pure unobtainium by scores of enslaved gnomes working 23-hour days in a forge fired by an active volcano beneath my shop. (really, I use tight-tolerance stainless steel barrels and huge accumulators) Good paper on cannon theory and thanks for the data.
Nice Carl, What you've said is pretty much right on. In fact you would get better estimates using the using the ideal gas law to get the pressure time curve like you mentioned, still have to deal with blow by and other losses. pumping more volume of gas in behind the projectile does and will increase you velocity but not above the max values listed. actaully predicting the muzzle velocity even if you know the pressure curve in a real gun isnt very easy due to all this stuff. one of the guys I work with has to do this for part of his phd thesis and its not anywhere near easy even with the nice modeling software and supercomputers we have. however it really doesnt matter for big gun since you guys have th foam test and that pretty much limits muzzle velocity for a given projectile so if you get that you can accurately predict the momentum and kinetic energy of the projectile (mv and .5mv^2 respectively) do big gun cannons have a oring you can tweak to increase shot velocity? In small gun that makes the penetration test pretty cumbersome since we normally retweak between battles and testing 2-6 cannons per ship before battle would take forever at NATS when you have that many ships . we were having this disscussion on the MWCI list and nobody have a good simple way to test velocity(since in the end thats what matters) quickly and easily. I think we'll just let cannons keep evolving till the average battle velocities start getting close to being dangerous which from what Ive heard and read about bbs is around 300 fps maybe a bit higher. (note those numbers arent that great cause there are more factors than that which determine if a round will break your skin)
I think someone is bringing a chrono to the next Nats to gather some data. My guns are nowhere near that fast, so I'm not worried (I use geek breech guns, so no tweaking for ultimate cosmic power Generally, I'm happy if they all work. Actually, if everything else on the ship works, I'm happy as long as I'm on the water.
Yeah there was a chrono at NATS this year, they were testing some guns and the fastest anybody shot was like 270-280 ft/s. but you cant battle at that tweak that was just how hard can you shoot. when they are down a a battle tweak the guns seem to be in the 180-220 ft/s range. I dont think any geek guns were tested, if they were i don't know the results.
My guns are the same design as Brian Koehlers, if they got tested. If Charley Stevens and Don Cole were shooting 270-280, I'm probably in the 180-200 range. It's enough to break balsa, just not from across the pond (I didn't name Charley and Don to complain, they're my friends. I named them because they have the most powerful guns I can think of in Region 3)
