Do 7/32" cannons penetrate better than 1/4"?

For that matter do BBs?

It is obvious that when you have two objects moving at the same speed, the heavier one will have more kinetic force.

• 
  However:
• 150psi cannon also have to accelerate that mass. A heavier object will accelerate slower than a lighter one. So it will take more cannon length for a 1/4" to gain the same speed as a BB. Therefore, it makes sense a shell that is "too large" will have less kinetic energy than a BB. Where is that "optimum" point?
  
• A larger bearing has more surface area than a smaller BB therefore will be slowed down more when traveling through water. However, it will also have more mass to counteract that drag. It is possible that water can slow down a 1/4" bearing considerably more than a BB.
  
• When a larger bearing impacts the surface of a ship, it will try to damage a larger area than the smaller BB. It is suggested that on thinner balsa, bearings can actually "tear" through therefore creating a larger hole.

I think its obvious that a larger shell will have more penetrating power than a smaller shell... up to a point. The topic of this discussion is, at what point will that power actually be reduced?

 

Most, if not all, Big Gun clubs use foam penetration testing to set gun limits. I'd expect this to equalize the different calibers in terms of force delivered, since everything gets fired into the same foam at the same distance. I think most people tend to crank up the power as much as they can get away with, to get as far into the foam as possible while not going all the way through.

Now, if guns were limited by velocity or pressure, & all were set to be equal, I'd expect different penetrability by caliber. Where the standard is penetrability of a common material at a common distance, I wouldn't expect much difference in actual power. At longer ranges, though, one size may retain more velocity & therefore more punch. Likewise, whichever size loses velocity the soonest probably comes out of the barrel the hottest, & might have better penetrating power close in. I doubt if it would be easy to detect or measure, though, or worth the trouble to try to exploit (vs. putting that time & effort into more productive exploits, such as practice).

JM

 

I'll second John on this one. Practice is the most important. This is a mute point if you can't hit the target.

Another factor that I think is more relevant is as far as the Indiana style cannon (as produced by Bill N and Jason A) there were only 2 sized made, 3/16 and 1/4. The 7/32 used the standard 1/4 cannon and the BB the 3/16. This made the cannon shoot irregularly and tougher to dial in that extra punch, and stay legal.

As far as kinetic energy, its not that simple. Kinetic energy is mass*velocity^2. Increasing speed increases the energy faster than increasing mass. I figured it outone time and will see if I can find my calculations.

1/4 balls tend to cause more damage (bigger hole). And yes, they can rip the thinner balsa easily. As a former cruiser Captain, I can tell you I dreaded the day a BB got an angled shot on my bow.

 

Actually, kinetic energy = (1/2)mv^2 but that's really just a nit & the point is still valid.

My point was that it's really kinetic energy that we test for in the foam penetration tests. All else being equal, except for the size & velocity of the ball, pretty close to the same kinetic energy should be getting applied to the point of impact. The difference should be the friction of the ball through the foam, which is roughly proportional to the cross-section & velocity, assuming that the foam can be treated like a fluid.

The formula for calculating drag is:

f(drag) = -(1/2)CpAv^2 where:

- C is the drag coefficient, 0.5 for a sphere
- p is the density of the fluid
- A is the cross-section area

The drag formula looks a lot like that for kinetic energy, which is appropriate since the drag ultimately results in the loss of all kinetic energy in a moving object, as long as the object doesn't hit anything before its velocity slows to 0. Using substitution, we get the following:

m = CpA or, since C = 0.5 for a sphere, m = 0.5pA ; A can be calculated for any sized ball as pi * diameter

Mass of a steel ball can be calculated, since volume of the ball can be calculated & the density of steel is easy enough to look up. With that, one can solve for foam density.

With the density of foam known, along with the fact that all kinetic energy is absorbed in 2" of this foam, the kinetic energy can be calculated.

Various assumptions have been glossed over.

Have fun!

JM

 

John, you made a few mistakes in your calculations. first off, the cross-sectional area of a sphere is pi * radius^2, not pi * diameter. Second, your equation m = CpA has issues. Namely, it states that m (proportional to radius^3) is equal to a pair of constants times A (proportional to radius^2), in other words it says that radius^3 is directly proportional to radius^2, which is only true for radius = 1 or 0. I made the same calculations, and the source of the mistake is the use of an equation that only holds true when force is constant (which it is not).

I will run some simulations in a spreadsheet program to get a more accurate answer to this conundrum. The basic design of the spreadsheet simulation will be this:
*assume an initial velocity of 165 feet per second and position 0, for a 1/4" diameter spherical steel ball bearing.
*calculate the force of friction at the moment of impact, hereafter referred to as "T0"
*calculate the acceleration caused by the force of friction at T0
*move to time T1, where T1 = T0 + (delta)T and (delta)T equals some small amount of time, maybe 1 millisecond or 1 microsecond
*calculate a new velocity based on the previous velocity, the previous acceleration, and (delta)T
*calculate a new position based on the new velocity and (delta)T
*calculate a new force of friction based on the new velocity
*calculate a new acceleration based on the new force of friction
*move on to time T2
*repeat until either velocity 0 fps or position 2 is reached, then revise simulation and repeat.

By adjusting different values, I will be able to get a useable density for the foam, velocities of other calibers of projectile, minimum velocity to penetrate 1/8" balsa, and other data on penetration. I'll report back once the calculations are done.
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edit: The simulation was a failure. To begin with, my computer model determined that the approximate density of the foam was 17500 kg/m^3, whereas water has a density of 1000 kg/m^3. In reality, the foam floats on water, and therefore must be less dense than water. Then, my computer model determined that the penetration velocities of 7/32 and 3/16 bbs were 280 and 690 fps, respectively. Lastly, the model predicted that .177" bbs CANNOT penetrate foam, no matter how fast they go, and in fact they penetrate LESS when their velocities exceed 1000 fps.

The primary source of error is most likely the use of formulas designed to model friction from a gas for calculating penetration through a solid. These states of matter are not interchangeable, and formulas intended for gasses do not yield accurate results when applied to solids.

In order to properly answer the question of cannon penetration, a different experiment is needed, one that uses experimentally determined data to generate a computer model, rather than the other way around. In effect, you must experimentally determine NOT ONLY the maximum legal velocity of each caliber of cannon, but also the velocity of each caliber projectile at several different points within the 2" test foam. Other data worth gathering is the minimum velocity of each caliber projectile necessary to penetrate the various thicknesses of balsa wood.

If anyone wants to see my model or more information, just let me know.

 

OOPS!! You're right, I posted the equation for circumference, not area.

As for the other, something had been bothering me about that. Specifically, it seemed to me like there was a missing component of distance, to account for how much through the fluid/foam/whatever the object penetrates. You may have found it for me. That would make radius^3 proportional to radius^2 * distance (travelled through the medium before velocity is reduced to zero). It's bound to be more complicated than just that, but I think that's getting closer.

My main point, though, was that since we measure penetration through a certain thickness of foam, we are really setting a limit on the kinetic energy delivered at the measured fixed distance. Since the masses of the different-sized balls are different, to deliver the same kinetic energy at the same distance, the velocities will have to be different as well. A graph of kinetic energy vs. distance for each size of ball should have all of them crossing at the 12" distance (discounting the drag through the foam by different-sized balls).

JM

 

I changed the testing medium from 2 inches of foam to 2 feet of water, and got somewhat better results. It's still not great, but at least this time I'm using a fluid medium rather than a solid one. I then calculated the energy for each, and I got a wide range of different energies. Turns out the 1/4" ball has the least starting energy, and .177 bbs have over six times the starting energy as the 1/4" ones. The interesting part is that the smaller the ball, the faster it loses its energy, so by .01 seconds after impact, the 1/4" ball has the most energy. The other interesting part is that in that same .01 seconds, the 1/4" ball travels the least distance.

Basically, I don't think the penetration test measures energy, but we won't know for sure until we run some real-world tests. Without real, measured data to support or disprove these claims, it's all just hot air we're spewing.

 

Here in Australia, we are strictly limited by law on our muzzle velocities, and as such do not use any penetration test. (far too inaccurate). We test for muzzle velocity instead.
What we use is a paintball velocity gauge, with an adaptor to allow it to be fitted directly to a cannon.
The upshot of this is that, for us, smaller caliber guns hit with less force than larger ones, just like in real life.

 

our own limited & less-than-satisfying tests showed velocities all over the place for multiple shots from the same ship/same gun with no adjustments in between. Is that consistent with what you've seen? Can you recommend any particular equipment to measure?

JM

 

I'm interested in the velocity guage. How expensive is it? How difficult is it to use? How consistent is it? Acurately measuring velocity is the most important step in determining the effectiveness of a cannon (what pressure does it need to get up to speed, what speed does it take to penetrate armor).

 

Carl forgot one thing... where do you get one? Any paint ball store?

 

The gun timer is labelled "VLOCITY Viewloader", and cost the club $65.00 Australian. I made the adaptor to fit it to the gun barrels using acetal and poly pipe. It reads number of shots, ft/sec and stores the highest recorded speed till reset. Not sure of what system it uses to measure the speed, I just accept that it can.

 

wow. I cannot wrap my head around this one. LOL Although I will tell you that BB damage is just as lethal as bearings. Think about this. Curt lines me up with his dual sidemount on Yamato. I'm coasting in with North Carolina. I have no power on five. He blows both mags (100 shot into my poor girl) and disintigrates eight inches by three inches from my starboard hull around "b" turret. Very impressive. I sank five seconds later.

Cumberland was sniping at Mini-CANNATS last year and hit from about twenty feet out on Scharnnie.

I say they penetrate just fine.

 

I am very happy with the penetrating power of a .177 size bb at 120 to 150 psi. Works very well. No matter what your style, they are required to penetrate a penetrable hull, not a impenetrable hull. Happy punching holes in soft balsa.

 

I only have experience with Big Guns, but I can tell you in the 6 years I have been involved in this hobby, I cannot remember a ship ever being sunk by BB's or 3/16's, but only 7/32's and 1/4's. Even when I had a cruiser, I ignored the BB's.

Andy

 

So is it useless for a cruiser in Biggun to Broadside a large battleship becaue it's bbs cannot penetrate the thicker balsa? Historically that would be accurate.So are cruisers in Biggun limited to attacking ships with equal balsa thickness and cargo ships?

 

They will penetrate, but the thicker balsa seals right back up. Once I was able to use a ligt cruiser and put 60 BB's in the same spot on a Richelieu and get it pumping hard, but it was never in danger of sinking.

I will clarify that these holes do count as points. They just don't contribute much to sinks, which is what I like.

Andy

 

Then 2 light cruisers should do the job. Where most of those holes below,on or above the waterline?

Hey saw on YouTube a very brief but cool shot of the stern area of a hood that had water in it and get this a couple of minnows swimming around inside it. Saw another video where a Biggun ship ram sunk and I do mean RAM a light Cruiser? Not sure but it rolled over pretty quick and sank. The video title says "SPEED BUMP" .

 

It's more of a physics question, really. You've got two projectiles, 1 and 2, of identical material and shape, but different sizes. These two projectiles penetrate the exact same distance into solid substance A. What happens when you test them on solid substance B? Honestly, we really don't know. I've got circumstantial evidence and arguements saying both YES and NO. Until we do some detailed experiments, no conclusive answers will be reached.

 

Back to the on water tests I say. Still though very interesting thread.