Measuring Cannon Ball Velocity

[CrufflerSteve]

I just did some testing of a handgonne and it made me wonder if there is a somewhat affordable way to measure the velocity of a cannon ball?

I used my old reloader's chronygraph for testing. For those who've never used one, it has two 'V' shaped pieces with a sensor in the bottom. They are seperated a fixed distance like two or 4 feet. The shadow of the bullet passing over the first sensor starts the measurement. The shadow of passing over the 2nd sensor ends the measurement and its displayed usually in feet per second.

The problem is that this device is fairly small so something rather inaccurate would not pass through the middle but blow the who thing up.

I've also had problems using it with BPCR loading I've done. BP makes smoke and there usually wads in those rounds which confuse the chrony.

A cannonball is followed by the great cloud of smoke and perhaps pieces of the bag for the BP. If a sabot is used for the ball, there is more stuff flying downfield.

I saw some radar chronygraphs which seemed to be exclusively for paintball.

I just wondered if there was anything out there for non-millionaires.

Steve

[Dirigo]

i heard the trick was to put up cardboard in front of the chono to catch the debris

[GGaskill]

Depending on the accuracy of measurement desired, one could put contact microphones on two large pieces of cardboard or thin plywood or frames covered with paper, connect them to the chronograph and fire through the sheets.  This would likely require a special chronograph or at least some kind of special interface into a standard one.

On the other hand, if you are using a large shot, it might be possible to remove the triangular shades from a skyscreen and fire over the bare photodetectors.

Or one could resort to the old ballistic pendulum, although for large shot, the swinging weight (bob) would have to be pretty heavy.

[Cat Whisperer]

xWEHRMACHTx  Welcome to the forum!


Some have built steel deflectors, probably good for the times when you're firing full auto or have had too many beers.


Interesting problem.  Need two switching devices and an accurate time-base to count the time between and a known distance.

[GGaskill]

It ought to be possible to use a laptop and some specialized (but home makable) screens for this.  I am looking into it.

[Will Bison]

Velocity measurement of cannon balls has been a project that I too have been working on since last Spring.

GGgaskill suggested a form of blast shield to reduce the effects of smoke and debris. This seemed like a logical approach. After some experimentation I found that a two inch thick, laminated wood shield angeled at 45 degrees would stop some of the blast. The shield was placed at 10 feet from the muzzle. (An earlier test resulted in a catastrophic and spectacular destruction of the shield) The angle shield deflected most of the blast upward.

A dummy chronograph was constructed and placed in front of the shield, still too much blast. The dummy and tripod went head over heels. A second shield was placed an additional 5 feet down range to further reduce the smoke and debris.

The next problem arose from the supersonic shock wave from the ball. The second shield stopped virtually all of the visible smoke and blast but the overpressure from the ball continued to wreak havoc on the dummy chrono and the tripod. Further testing was suspended at that point.

The second method employed involved the use of an electronic stop watch and a GPS. I utilized an assistant to fire the gun while I moved off a distance and observed the emergence of smoke from the muzzle and the impact of shot. While this method is not perfect it did produce the best results thus far.

Some practice is required with the stop watch and this was accomplished with a rifle and black powder. After considerable practice I developed the eye/hand response required for this rather unscientific approach.

We then commenced shooting three rounds at various ranges. Thus we picked random targets and fired three shots at each observing the fall of shot on each. Once the shooting was complete, we simply measured the distance to each target with the GPS. I placed a MOB at the gun position and then from each target I selected a GOTO and aquired the distance.

Now that I had the time of flight and the distance I could compute the average velocity for a multitude of ranges. When more data is gathered I should be able to construct a graph and interpolate velocity at various distances.

So how fast does the ball go?? At this point we estimate a muzzle velocity of about 1,240.

Test specs are as follows: The tube is 47mm, rifled, 28.5 inches length of bore. Ball weight is 8,780 grains. Powder charge 2,500 grains GOEX 1f. All balls and powder weighed on a digital scale for consistency. Ball is patched with .015 ticking to prevent the ball from rolling forward in the bore. Ball is pure lead. Powder is contained in a standard aluminum foil packet.

As I get more info I'll pass it along. If it's not obvious, all this testing has consumed a considerable amount of time not to mention the quantity of powder and lead.

Bill

[CrufflerSteve]

GGaskill and Will have some really good points. My favorite cannon has a 2" bore and it is machined steel so it is strong. With 2 1/2 ounces of powder it produces a huge plume of rapidly moving smoke. Unfortunately, its in a naval carriage and is low to the ground.

Will's idea of a blast shield at a 45 degree angle is a good one. Perhaps 45 and angled like the snowplows for a train so it diverts some of smoke to the side. The chrony could then be placed in a trench behind it for even more safety. If I made sure the trench was deep and it wasn't noon so the sun was directly on the sensors, they might pick up the shadow of the cannonball. I might be able to try this test later this month. I will try the test without the chrony but something light and fragile in the trench to see if it survives first.

Steve

[Powder keg]

Hi, Rick Neff, one of our sponsers has done this. I'll call him and have him post details. He some times gets to busy to view the board every nite. Later, Wes

[CrufflerSteve]

Just to give an idea what you're dealing with, here's one a fraction of a second after ignition:


I'd say getting muzzle velocity would darn't near impossible but far enough downfield, you could have the blast shield and chrony in a trench.

Steve

[Powder keg]

Smokin!!!

[GGaskill]

OK, so what's all the yellow smoke from?

[Powder keg]

Yea! Why's the smoke Yellow?

[Double D]

What did you blow up?

[CrufflerSteve]

What did you blow up?

I didn't blow up anything. That shot actually hit dead in the middle of a target that you can't see for the smoke. The projectile was a lead ball. The range wasn't that great. Here's a higher res picture:
http://www.crufflersteve.net/cannon_fire.jpg

The powder used was 2.5 ounces of Skirmish 1f. This picture is within a tiny fraction of a second from ignition. If you look at the picture it looks like a piece of the aluminum foil powder bag is flying downfield.

The yellowish color could be some digital artifact of capturing a rapidly moving cloud of smoke or it might have been yellowish at first. After the shot its the usual cloud of white smoke.

Steve

[Will Bison]

The Yellow smoke is from the aluminum combusting. I normally get a ton of Yellow smoke from canister shot as I wrap the canister in foil as well as the powder charge.

Steves photos are quite graphic and are a good indication of the volume of smoke that must be redirected to get valid results from a chrony.

When I built my blast fences, I put a three inch hole in them for the ball to pass through. The first shield passed quite a bit of smoke, the second one stopped it but of course did nothing to mitigate the overpressure from the ball passing over the dummy chrony box. My dummy sky screens went away.

A ballistic pendulum would have to be quite substansial I would think. I know what my little gun does to an automobile when it hits the engine block. I think Phil Sharpe or one of the other older gun writers explains the ratio of pendulum weight vs ball weight.

If Rick Neff has some data or design ideas, I for one, would be interested.

[GGaskill]

If you could fire iron shot, an inductive screen would ignore all the rest of the junk.

Ackley talked about a ballistic pendulum.  From memory, he said to use a 150 lb bob for .450 magnum class cartridges.

A 1 lb shot at 1200 ft/sec would impart 7.95 ft/sec velocity (and 147 ft lbs energy) to a 150 lb bob which would be enough to lift the bob almost exactly 1 foot.  With 10 foot support cables, that would give the bob a swing of 4.36'.  I think Ackley said that you want to keep the swing down to about 6 inches or so.

[CrufflerSteve]

If you could fire iron shot, an inductive screen would ignore all the rest of the junk.

Ackley talked about a ballistic pendulum.  From memory, he said to use a 150 lb bob for .450 magnum class cartridges.

A 1 lb shot at 1200 ft/sec would impart 7.95 ft/sec velocity (and 147 ft lbs energy) to a 150 lb bob which would be enough to lift the bob almost exactly 1 foot.  With 10 foot support cables, that would give the bob a swing of 4.36'.  I think Ackley said that you want to keep the swing down to about 6 inches or so.

Which would be a darned big bob. Big rack to hold it on, cables and such. It would probably be harder to transport then the cannon.

I am thinking of Will's blast shield idea. I have no ambitions of trying to shoot through a small hole. If I make it great, if I don't I make a heck of a mess. To have any hope of shooting through the hole, it would have to be close to the cannon where the blast would be intense.

The cannon I want to test is close to the ground. That means that it picks up debris from the ground as well as from the shot. Here's another picture. I won't shrink it to be official but just put a link:
http://www.crufflersteve.net/fire01.jpg

I am thinking of a blast shield about 1 foot to 18" high. It would have the 45 degree angle with a V shape to divert to the side. That would stop some debris and move some smoke aside. It would be sturdy and staked to the ground. If I put it 20 yards or so downfield and had a chrony in a trench behind it, I might get something. The smoke and debris moves fast, but much slower than the shot. By keeping it a distance away, the ball would arrive much sooner and the chrony might have finished the measurement by the time the smoke arrives.

Steve

[Will Bison]

There is another way. I just remembered it. Two discs each rotating at a known RPM on a common shaft. The discs might be three feet or so in diameter and spaced two or three feet apart. The disc diameter and spacing is not too critical.

The common shaft is aligned parallel to and off to one side of the bore. The ball passes through the first disc and since the discs are turning, the hole in the second disc is not in line with the first.

If we know the RPM we also know the revolutions per second and we know how far the first hole moved in relation to the second hole and of course we now know the MV. That is if we do the rest of the math.

Bill

[Cat Whisperer]

There is another way. I just remembered it. Two discs each rotating at a known RPM on a common shaft. The discs might be three feet or so in diameter and spaced two or three feet apart. The disc diameter and spacing is not too critical.

The common shaft is aligned parallel to and off to one side of the bore. The ball passes through the first disc and since the discs are turning, the hole in the second disc is not in line with the first.

If we know the RPM we also know the revolutions per second and we know how far the first hole moved in relation to the second hole and of course we now know the MV. That is if we do the rest of the math.

Bill

One disk can be fixed, or if the location of impact can be controlled (known) the angular change of the disk can be determined with one disk.

[Double D]

Why not use the old wire grid method lke chrongraphs use to use.  In fact I seem to remember reading some where that Oehler chronographs can still use these by changing some switch settings.  Drop Oehler an email and see what they have to say.

[GGaskill]

Email has been sent.  It may take a while; the last email I sent them took a few weeks to be answered (probably an anomaly.)

[Cannonmaker]

I have been busy with a contract and had not much time left at the end of the day.  Will soon slow down and be able to start on a couple of Coehorns.

When I Chronograph the Cannons I find the following works the best.

I place the Chronograph apx 5" from the muzzle of the Cannon. This allowes the muzzle blast to pass through the Chronograph with out any destruction.  Place some weight in the chrony to keep it stable.  Tape  the Polymer strap to the rods holding them up. Tape only the very ends, light must pass through those straps.  Have a bright sunny day, although I have had good luck using lighting overhead when the clouds moved in.  Use warm water and clean the Polymer strap after each shot,  if not you will not be consistence in your readings.  I prefer to shoot at least 8 shots, not counting the fastest or the slowest and take the average of the rest.

This works best for me, good shooting to all, Rick

[Cat Whisperer]

Is that 5" in front of or 5" off to the side - or both?

I have a picture (somewhere) of the 1" board (3/4" thick) used to adjust the elevation on my 4.5" mortar that was a little longer than needed and stuck out past the muzzle.  The muzzle blast snapped it off.  But then, mortars are short barrelled too, so that might be a bit different.

[Powder keg]

Sounds like fun Rick. We'll have to check a couple of my guns one day. I've got a 1/3 scale 24 pounder that would be fun to check.

[Cannonmaker]

ca,  It is 5" right in front of the Muzzle.  The ball enters the Chronograph 5" from the muzzle, as close to center as possibly.  the smoke  and concussion follows through without much problem. Much more distance on these larger bore blows the top off  the Chronograph.  I have measured from 1" to 1-15/16"  (1/3rd 24 pdr Field Howitzer, bore to scale).  The 24 pdr. actually looks better when bored for golf ball.

[Cannonmaker]

Woops,  I meant to say
           CW,  Its 5" from----   Rick

[Cat Whisperer]

That's interesting.

It means that with the cannon the column of gasses is moving very fast and with the mortar it's still expanding.

That would also be consistant with the difference in the sound of the firing of both - as well as in pistols vs. rifles.


Thanks.  Another piece of information in the overall puzzle we play with.

[GGaskill]

I got a reply from Oehler regarding the use of "wire grid" screens with their chronographs.  I have a Model 33 which should be adequate for this kind of activity. 

It requires making a couple of special cables to connect the "grids" to the chronograph but the degree of specialness is quite small.  Anyone who can do electronic soldering can make them.  Parts required (for one cable) are a male phone plug, an adequate length of wire, two 10K resistors and the grid screens.  The easiest way to do this is to incorporate the resistors in the screen instead of the cable.

If you are interested, I can email a copy of their .doc file with the diagram.

[GGaskill]

Diagram added to above post.