Thursday, December 31, 2009

The ballistic pendulum

by B.B. Pelletier

Many of you have wondered how the gun makers of centuries past were able to test the power of their guns. This blog has touched on a few of the ways gun power was measured over the years, with the Splatology discussion being the most significant. If you are not aware of that report you really need to read it, because it's the Rosetta stone that unlocks the mysteries of the past when it comes to airgun power.

Another way the shooters of history determined relative power was by the use of the ballistic pendulum. You can find a wealth of information about the ballistic pendulum online. Just do a Google search for ballistic pendulums and see what turns up.

The first big bore airgun match needed a ballistic pendulum
My own experience with ballistic pendulums dates back to the time I ran the first big bore airgun match at the August 1998 Mid-Atlantic Airgun show. I needed a way of determining the relative power level of the guns in that match and, even though we had and used modern electronic chronographs to record the power of the guns, I wanted something more--something that visibly showed the power so everybody could see it. I wanted what didn't exist at the time--a ballistic pendulum for big bore airguns.

Gary Barnes was helping put the big bore match together, so he took on the project of building a ballistic pendulum for it, too. What he wound up building was a large spidery machine with a 4-inch steel plate the shooters had to hit. I wanted the match to be challenging, so we placed the pendulum 40 yards from the firing line. Believe me, in 1998, hitting a 4-inch target at 40 yards with a big-bore airgun was considered a big deal!


The ballistic pendulum was two feet high and four feet long.



A pen under spring pressure recorded how far the pendulum arm swung.



The steel plate was backed by more steel to make the pendulum arm heavy and to strengthen the plate.


Put up or shut up
In fact, hitting the target at all was the principal motivation for building the pendulum the way it was made. At the time, there were all sorts of stories circulating about super-powerful big bore guns with unbelievable accuracy. Among them, some smoothbore Farco air shotguns were supposed to be getting 2-inch 5-shot groups at 50 yards. Yeah--right! We ran this first-ever modern big-bore match as a "put up or shut up" affair, and not surprisingly a lot of shooters had to shut up.

At the first match, there were several guns that could not hit the target even one time in five shots. Out of 11 shooters, only 6 managed to hit the target even once out of five tries, and one of the six just scraped paint off the edge of the plate without recording any energy on target.

The score was determined by a combination of hits on the 4-inch plate and energy recorded by the pendulum. That last part was very arbitrary, as I will discuss in a moment, but back to the scoring. The more energy a gun had, the higher number of points were given for each hit on the plate. Powerful, accurate guns were rewarded, and weaker guns that were still accurate were penalized. The thinking behind that was that we wanted to reward power in combination with accuracy.

The lessons of the pendulum
How the first match turned out was less important than the lessons that the big pendulum taught us. First, it taught us that no rifle can ever expend all of its energy on a ballistic pendulum. How much it does expend is really how much that gets recorded, and that can only ever be a fraction of the total energy available. Let's look at some energy thieves and learn why ballistic pendulums aren't foolproof.

1. Loss of energy through projectile deformation
When a bullet hits a steel plate of any mass, it deforms, taking some of the impact energy with it. If the bullet hits at a very high speed, the deformation is more violent, robbing more energy. A lightweight bullet from a high-power centerfire rifle, for instance, will turn into lead powder and guilding-metal fragments, with an accompanying flash of light caused by the heat of impact that flashes some of the lead dust to incandescence. A slower, heavier projectile will not fragment as much and will impart greater energy to the target, causing the pendulum arm to swing farther. A ballistic pendulum constructed as this one was will show that a 400-grain bullet moving at 750 f.p.s. has greater energy than a 55-grain bullet moving at 3,200 f.p.s., even though the smaller, lighter bullet actually has more than twice the energy of the larger bullet.

This bias can be offset a little by selecting a different medium for the target. For example, if a big log is used and positioned to be hit on the end by both bullets, the smaller bullet will make a much better showing. That's because the log will absorb more of the bullet's impact energy without allowing as much deformation.

2. Friction
The pendulum has friction in several places. The arm that swings has bearings with friction, and the pen that records the energy also has some friction. Granted, these are both small forces, but they're still real and they do matter. Barnes made the arm of the pendulum ride in a long bearing that was oiled and exercised frequently, but it still retarded the swing angle of the arm.

3. Gravity
As the pendulum arm swings, it soon comes under the influence of gravity. The moment it swings past 90 degrees, gravity starts pulling at the swinging arm, slowing it down.

4. Glancing blows
When the bullet hits the plate, the plate begins to move. The bullet expends its energy by deforming, breaking into dust and flashing to incandescence, but it also glances away from the plate fairly fast. As it goes, it carries some energy with it. Other ballistic pendulums have been built with bullet (pellet) traps in their pendulum plates. The plates were shaped like funnels, so the bullet was deflected ever inward and continued to expend energy against the plate.

The energy thieves were but one lesson the pendulum taught us. Another was how arbitrary our measurements really were. If you look at the lines drawn on the scorecard, they're supposed to represent foot-pounds of energy. Even when I made up the scorecard, I knew I was drawing the lines arbitrarily because I had no good way to calibrate them. Oh, I did shoot a few rounds with a blank scorecard in the machine so I could get a rough approximation of the energy needed to deflect the pen, but it was far from accurate or exact. It was never calibrated because I had no good understanding of how the energy thieves acted. Nothing was linear, either. As I mentioned earlier, a light, fast bullet was penalized, compared to a slow heavy bullet. The farther the pendulum swung, the more gravity acted upon it.

The next year, Ray and Hans Apelles showed up with single-shot Career 9mm rifles. We had added a 50-yard accuracy test to the ballistic pendulum test and they taught us another lesson. On the pendulum, they used a bullet that weighed over 175 grains, if I recall. I think it even weighed over 200 grains. But it was hell on the pendulum, with most shots smacking the plate sideways or nearly so. It did what they wanted it to do. But on the target at 50 yards, they used a 9mm pistol bullet that probably weighted 115-125 grains. Far more stable and accurate at airgun velocities.


Gary Barnes shot a .563 Express to win the match.



Bob Chilko shot his homemade .398 multi-pump pneumatic.


The Chilkos
We learned another big lesson about big bore accuracy from the team of Bob Chilko and his son, Mike. They competed with their homemade smoothbore big bore guns. Bob shot an underlever and Mike shot a front-pumper that took 30 strokes to pressurize for every shot. Mike hit the 40-yard target four times in five shots and had everyone talking. How could he do that with a smoothbore? It turned out Mike, who was a physicist, had designed dumbbell-shaped slugs for both guns that had such high drag they flew accurately without a spin on them.

I noted that within the year, Gary Barnes was selling similar bullets for his big bores, and they pushed the distance at which his rifles were accurate from about 50 yards to 200! He called them Hornets, for the noise they made in flight. These bullets were a reincarnation of the French Balle Blondeau shotgun slug of the 1960s that revitalized the rifled slug industry.

So, the bottom line with the ballistic pendulum was that it provided everyone with an extended course in practical physics. In a world where accurate electronic chronographs abound, there isn't much reason to have one of these. But at one time, they were the best that money could buy.

44 Comments:

At December 31, 2009 5:54 AM, Blogger Slinging Lead said...

December 2009 Index

1. Tennis, golf, baseball, football (Edith)
2. Relum Supertornado - Part 3
3. Christmas gift list 2009 - Part 2
4. Making lemonade
7. Air Arms S200 Sporter - Part 1
8. Micro Desert Eagle concealed carry gun - Part 1
9. Colt Defender BB pistol - Part 1
10. Christmas gift list 2009 - Part 3
11. The Red Ryder - Part 1
14. Ruger Explorer - Part 1
15. Christmas gift list 2009 - Part 4
16. Ruger Explorer - Parts 2 & 3
17. Air Arms S200 Sporter - Part 2
18. The Red Ryder - Parts 2 and 3
21. AirForce Edge - Part 1
22. Colt Defender BB pistol - Parts 2&3
23. Daisy 25 dating information - Part 1
24. AirForce Edge - Part 2
25. Merry Christmas, an unusual Crosman 760
28. Healthways Plainsman BB gun - Part 3
29. Doing strange things with airguns
30. AirForce Edge - Part 3
31. The ballistic pendulum

 
At December 31, 2009 6:37 AM, Blogger Lloyd said...

B.B.,
Very interesting blog. With all the variables you pointed out, it really emphasizes that there is a lot more to the actual effectiveness of a hunting bullet than a simple FPE calculation.

I read about someone shooting different ammo into a wet clay river bank and assessing the shape and volume of the resulting hole. Pretty arbitrary, but like the ballistic pendulum, fun.

Best regards,
Lloyd

 
At December 31, 2009 6:45 AM, Blogger B.B. Pelletier said...

Lloyd,

Funny you should mention the clay, because we toyed with the idea of using bales of wet newspaper before settling on the ballistic pendulum. The newspaper was too difficult to handle in a match, plus the logistics of getting it ready were overwhelming.

B.B.

 
At December 31, 2009 7:04 AM, Anonymous Michael in Florida said...

BB,

Wishing you and your readers a Happy and Prosperous New Year.

Regards,
Michael in Florida

 
At December 31, 2009 9:10 AM, Blogger kevin said...

I sure like these articles. A look into the past for a glimpse of airgunning grass roots.

Although 1998 is not the distant past, relatively speaking, I doubt many people (me included) imagined the innovations taking place in big bore airguns. This is certainly a realm of airguns that few even considered. This handful of airgun enthusiasts, physicists and garage inventors had to create electricity in the air when they all got together in one place.

I'm trying to imagine the serious conversations by experienced and dedicated shooters brainstorming about a device to accurately measure energy from a big bore airgun. Had to be fun. I know if I would have been lucky enough to be there my wife would have rolled her eyes (again) and uttered her famous phrase, "He reached the age of 13 and quit maturing."

Dumbell shaped slugs in big bore airguns. Never gave it a thought. We used to shoot these in shotguns but they were called bobbins.

The best part about today's article is knowing there are airgun addicts that have it worse than me. In my mind if you design an airgun that requires 30 pumps per shot you've reached the pinnacle of this sickness.

kevin

 
At December 31, 2009 12:06 PM, Anonymous nbumpo said...

I just got a new Daisy 953, and the "Introduction Guide to Competitive Shooting" that came with it lists among the available accessories a sling bracket and a nylon web sling.

I can't find these anywhere on the Daisy or Pyramyd web sites.

Anyone know where to get them?

(The Daisy phones are shut down for the holiday.)

 
At December 31, 2009 12:07 PM, Blogger Albert said...

BB,

Thanks for another great article. Surrounding this topic of discussion, do you happen to know the ballistic coefficient for the Eun Jin 32 grain pellet (or someone who might know?) It is an excellent projectile for my Sumatra 2500 rifle in terms of power and accuracy. After cleaning the barrel per your recommendation and passing the break-in period, the rifle is producing a maximum muzzle velocity of 1020 ft/s with this pellet. Shooting them between 990 and 965 ft/s averages 1 inch (5-shots group) at 50 yards. I am really interested in finding out the long range performance of this pellet and found a ballistic calculator on the web. But it requires the ballistic coefficient as one of the inputs:

http://www.realguns.com/calc/exteriorballistics?calc

Thanks,
Albert

 
At December 31, 2009 12:25 PM, Anonymous Anonymous said...

nbumpo,

Congragulations on your new air rifle. I receaved a 953 for Christmas last year and love it. I to have wanted a sling and mabe those target sightes but I couldent find out where to get them. I dident call daisy though. The sights are kida cheap from them to. I`ll be interested to hear how to get those to.

Anon.

 
At December 31, 2009 12:36 PM, Blogger kevin said...

Albert,

You need the velocity at 2 distances, then use the online Troyer trajectory calculator. Or take your velocities to the Chairgun program. BC's are not a constant and vary as a function of several variables, but mainly velocity.

Here's a link to Brad Troyers BC calculator:

http://www.airguns.net/software_downloads.php

kevin

 
At December 31, 2009 12:49 PM, Anonymous Volvo said...

Despite being laid off yesterday, I still have hope for 2010 that will out shine ’09.

Happy air gunning to all in the New Year.

Volvo

 
At December 31, 2009 1:07 PM, Blogger BG_Farmer said...

BB,
It sounds like the Big Bore custom makers re-invented the wheel a little bit in terms of barrels and projectiles for accuracy. Most of the pieces should have been available from BP sources, with years if not centuries of testing behind them. 4" at 40 yards should have been child's play even with a patched round ball, assuming the rifling rate was correct, and plenty of suitable barrels are available for a reasonably low price.

I do like the machine, though. I need to build something similar, as you know we rednecks love reactive targets, whether they are scientifially valid or not. A lighted bar "power meter" on a pole above the contraption will provide adequate feedback:).

 
At December 31, 2009 1:14 PM, Blogger BG_Farmer said...

Volvo,

Sorry to hear about the job situation, but I know you've got the grit to come back out on top.

 
At December 31, 2009 1:53 PM, Blogger FRED said...

Nbumpo,

while it appears Pyramyd does not carry the Daisy brand of slings and swivels, they do carry some high quality aftermarket accessories. You can find it at this link:

http://www.pyramydair.com/a/Miscellaneous/Slings_and_swivels/49

I looked at the Daisy website and they don't list any slings or swivels so perhaps they have discontinued these accessories.

Welcome to the blog and good luck with your new air rifle.

Volvo, I guess the old saying is true, when it rains it pours. Good luck to you in the new year and to everyone on this blog, especially Edith and that ole rascal, BB.

Fred

 
At December 31, 2009 2:15 PM, Blogger B.B. Pelletier said...

nbumpo,

Daisy wrote the owner's manual years ago. But over the years their accessories change and nobody bothers keeping up with what's in the manual.

We are checking to see if an optional sling is available for this rifle.

B.B.

 
At December 31, 2009 2:16 PM, Blogger B.B. Pelletier said...

nbumpo,

I doesn't appear that Daisy has such a product, however if you call them they may have one in stock that they can sell you.

B.B.

 
At December 31, 2009 2:16 PM, Blogger B.B. Pelletier said...

nbumpo,

I doesn't appear that Daisy has such a product, however if you call them they may have one in stock that they can sell you.

B.B.

 
At December 31, 2009 2:29 PM, Blogger B.B. Pelletier said...

Volvo,

I'm sorry about losing your job. What a swell end-of-the-year present for you and your family.

B.B.

 
At December 31, 2009 2:52 PM, Blogger kevin said...

Volvo,

Sometimes great opportunity is well disguised.

Here's to a prosperous new year.

kevin

 
At December 31, 2009 3:21 PM, Blogger CJr said...

SL,
Thanks for the index.

BB,
Very entertaining and educational article.

You mentioned Champion's Choice in an earlier comment today and that reminded me that I got the target gauge with magnifier from them last week. It is really a very handy tool for verifying my competition POI's. It has made me both happy and sad. It certainly removes all doubt about when the pellet crosses the line and saves a lot of time I spent pushing a pellet through the hole for measurement.

-Chuck

 
At December 31, 2009 3:37 PM, Blogger Fred said...

Hi B.B.
I've really been learning a lot from your blog! I have a few questions for you. Please excuse me if I'm posting in the wrong place!

1. Posting to your blog:
Is it always best to post any question or comment to the newest blog, even if a former blog (say from 2007) is what the question is about?

2. I've just ordered a new 2300KT from the Crosman Custom shop, and a I have a nice Williams notched blade sight coming from Pyramid! This is my first Co2 gun purchase since recycling has become more available in most areas. Are the Crosman Co2 cartridges recyclable? What exactly are they made of? Can they be sorted in with aluminum cans? I can't seem to find a clear answer to this from google searches.

Thank you for your time!

-Freddie (another Fred on the blog)

 
At December 31, 2009 3:42 PM, Blogger B.B. Pelletier said...

Different Fred,

As metal the cartridges are recyclable, but not in economic quantities for shooters. They cannot be refilled.

B.B.

 
At December 31, 2009 3:43 PM, Blogger B.B. Pelletier said...

Different Fred,

Yes, it's best to ask your questions on the current blog, as only a very small number of people can see when you post to an old one.

B.B.

 
At December 31, 2009 3:54 PM, Blogger derrick38 said...

Volvo,

Sorry to hear about your job. Hang in there.

Derrick

 
At December 31, 2009 4:31 PM, Anonymous Mr B. said...

Volvo,

Truly sorry about your job situation. I have to agree with Kevin's comment to you. I got fired when my second child was two weeks old. Made a career change and retired from that job of thirty years 2 years ago.

God bless you and your family.

Mr B.

 
At December 31, 2009 4:34 PM, Anonymous Mr B. said...

HAPPY NEW YEAR TO ALL YOU WONDERFUL PEOPLE

Mr B.

 
At December 31, 2009 4:46 PM, Anonymous Scott298 said...

Good day B.B.--hope you and mom had a merry shristmas and are looking forward to a happy-new-year and that all is well.And yes iT's your adopted son, Scott298 checking in. B.B.--forget about price I don't want it to be an issue in your answer. I've been looking at new guns recently - especially Air Arms - and unless there is a specific need - are there any advantages to buying a pneumatic vice a springer rifle? Either rifle would be an air arms but does the mechanics of one outway the other and if they do - not doing any competition shooting, just the average guy with "the itch", where and when would these advantages really stand out? Hope all is well on your end-Scott

 
At December 31, 2009 4:47 PM, Anonymous Desertdweller said...

Happy New Year from New Mexico!

Sorry to hear about your job loss, Volvo, but a positive attitude like yours will go a long ways toward finding another. Wishing you all the best.

Les

 
At December 31, 2009 5:00 PM, Blogger donheatley said...

RE: Daisy 953. I bought one last year and contacted Daisy by phone for the sling, the sights and the sight inserts. Maybe they still have them

 
At December 31, 2009 5:09 PM, Blogger B.B. Pelletier said...

Scott,

A pneumatic rifle doesn't have any hold sensitivity. Therefor it's easier to shoot accurately. That's the biggest advantage.

B.B.

 
At December 31, 2009 5:25 PM, Blogger Albert said...

Thank you Kevin. Your information is very helpful.

I too hope that Volvo will get a better job soon.

Happy New Year everyone!

Albert

 
At December 31, 2009 5:33 PM, Blogger ajvenom said...

I just want to wish everyone a HAPPY NEW YEAR!!!!!!!

I often think about clean renewable resouces to generate electricity inwhich compressed air can be used for transporatation purposes.. Perhaps it can have a class of it's own on the drag strips someday.

 
At December 31, 2009 6:40 PM, Anonymous /Dave said...

Volvo,

Sorry to hear that. I've been in that position more times than I care to remember... Learn what you can from it, and continue. Many times, what I thought were the bad things in my life, were actually blessings n disguise. Good luck to you!

/Dave

 
At December 31, 2009 9:41 PM, Blogger kevin said...

It is my desire and wish that everyone have the best year yet!

Health, Happiness, Prosperity in that order.

kevin

 
At December 31, 2009 9:45 PM, Blogger kevin said...

Albert,

You're welcome.

You ask very relevant questions. Hope you become a frequent contributor.

A very Happy New Year to you.

kevin

 
At December 31, 2009 9:46 PM, Anonymous Wayne said...

Volvo,

Better things are coming for you and yours! You've been through way tougher stuff with your daughter. Life is still good!

B.B.

Excellent story today. Are the Hornet air bullets a similar design as the JSB domes. It seems like a design would work no matter what size you made it, if all other factors were the same.

That sounds like a fun event. Big bore air guns are on my wish list for next springs fun money.

Happy New Year Everyone!
May all our future days be in abundance of Joy and Love and money... and ammo... lots of ammoooooooo

Wacky Wayne, MD. Ashland Air Rifle Range

 
At December 31, 2009 9:49 PM, Anonymous Wayne said...

Happy New Year Kevin!

I owe you big time... I'll start payments in the new year!

"I'll gladly pay you Tuesday for some shotgun shells today"

Wacky Wayne

 
At December 31, 2009 10:14 PM, Blogger kevin said...

Wayne,

If you don't send me a bill I'll send guido after you. ;^) We had an agreement.

Gary Barnes hornet bullets were designed after the "bobbin" or "French Balle Blondeau shotgun slug of the 1960s" as B.B. more accurately describes them. They look nothing like a jsb. Think more along the lines of a barbell. B.B. mentioned the sound that these made when shot through the air with a big bore airgun, hence the name "hornet". (never heard that sound out of a shotgun but understandably so).

I think the design "innovation" has to do with smoothbores. A barbell or bobbin shaped projectile in a rifled barrel loses to a jsb design in my simplistic experience and way of viewing such things.

A very happy new year to you and yours.

kevin

 
At December 31, 2009 10:26 PM, Anonymous Anonymous said...

Happy New Year BB and gang.

This Blog is the best!

Brian in Idaho

 
At January 02, 2010 9:03 AM, Anonymous luke said...

Thank you BB, you just gave me my new year present! I've been waiting for this, hope i can find time to made one...

 
At January 02, 2010 9:19 AM, Anonymous Mr B. said...

Slinging Lead,

I agree with you 100%. A Weaver Rail doesn't aesthetically belong on a TX200.

Also thanks for putting together the monthly indexes.

Mr B.

 
At January 02, 2010 10:55 AM, Blogger CJr said...

Mr B and SL,
I agree with the aesthetic preservation of the TX200. But I think that all air rifles that have that assault look should have the Weaver/Picatinny rails. They do add to the meanness look of the rifle. And while we're at it couldn't we work on a Weavatinny or a Picaweaver rail instead of having to choose one or the other? Come on, if we're talking standardization, let's standardize.

 
At January 02, 2010 11:19 AM, Blogger CJr said...

Good news everybody!! Well, good news for me, anyway. I just won the December eMatch drawing again for a $10 PA gift certificate. I want to thank each and everyone of you for staying out of the competition so that my drawing chances are better.

For December I entered my Daisy 953 and my Talon SS in the benchrest, any sight match. And I got beat out again by that d**n Anschutz. At least I tied for third place. Does anyone know of an Anschutz weakness I can exploit with my 953?

The scores (max 300) follows:

Randy152 - Anschutz 8001 using Beretta Ultra mAtch pellets - Scored 284

Desert fox - Air Arms EV2 using Vogel 4.50/.53g pellets - Scored 271

Desert fox - RWS Diana mdl 75 using Vogel 4.50/.53g pellets - Scred 269

Chuck3e - Daisy 953 using JSB Exact 8.4gr - Scored 269

Chuck3e - Talon SS CO2 using Crosman Premiers 10.5gr - Scored 261

I know my T-SS can out shoot my 953 but it didn't this time. I can explain that by saying I shot the 953 30 times first and then shot the T-SS right after. I blame the diff on fatugue. Next time I will shoot them on different days or at least shoot the T-SS first and see if that makes a diff. I'm not doing too good on the 10's either. Dang those are small circles!

-C

 
At January 02, 2010 11:57 AM, Blogger ajvenom said...

Wow, nice shooting Chuck!!!!

I wonder how much a LW barrel would Help? I often use RWS R10 match sometimes. It all depends on the tin. Sometimes JSB exact heavies and sometimes RWS R10 rifle match.

 
At January 02, 2010 12:09 PM, Blogger CJr said...

aj,
I do have some R-10's. I think I'll practice with them a bit. They have worked well in my 953 but the JSB seemed to be better when I was testing. However, I could have just been having a bad day when I tested the 10's. Thanks for the reminder.

-Chuck

 

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