I have been wondering how the velocities were determined for all the classic british express and other classic big bore rounds of yesteryear. Any enlightened souls out there that know how the old timers figured velocity. Lets face it they didn't have photocells and digital timers in 1900!

I guess I have always questioned the velocities documented for the nitro express rounds, etc. My personal gut feeling is that these rounds were loaded to a copper crush pressure threshold and what ever the corresponding velocity was it was. In actuality I bet that the velocity was calculated and in no way ever verified.

Any other thoughts.

Todd E

They would shoot the bullets into a pendulum.

Knowing the weight and length of the pendulum, they could calculate how much momentum the bullet had by measuring how far the pendulum would swing after the impact. Knowing the weight of the bullet, they could then calculate the velocity.

Of course, as with any scientific experiment there were a million measurement variables (friction, wind resistance, etc) so accuracy was largely dependant upon who was running the show, but I think they were pretty darn accurate for 150 years ago.

[edit] Oops, make that 250 years ago.

[This message has been edited by Jon A (edited 01-16-2002).]

Todd,

Winchester 375 ammo has done 2450 with 300 grainers and about 2620 with 270 grainers since I had an Oehler in 1970. That was the Oehler 10 with paper screens.

That about match es the original ballistics for the 375.

If it was a "guess" it was a good "guess"

Mike

They weren't guessing, as earlier stated they used metal pendulums, I read it in a reloading manual, Lyman I think. It wasn't as fast as an Chrony, but pretty darn good for its time.
Good luck and good shooting

The ballistic pendulum is based on classical Newtonian physics and works pretty danged well to calculate velocity. It just goes to show that you don't need gee whiz electronic devices to do everything, just some simple principles that have been around for five hundred years or so.

As Jon A, Eterry and boltman stated it was probably by ballistic pendulum. What I find fascinating is how long it has been used.

(Alluding to ballistic advancements post Galileo)

"A clever way to measure bullet simply and accurately is with a device called the Ballistic Pendulum, which was invented a century later, in 1730, by Benjamin Robbins, an Englishman." (from MODERN PRACTICAL BALLISTICS by Prof. Arthur J. Pejsa)

The late Walter Roper had a detailed schematic in his book EXPERIMENTS OF A HANDGUNNER (if I recall the title correctly)

[This message has been edited by Scott H (edited 01-16-2002).]

Has anyone ever correlated a ballistic pendulum with a chronograph to determine the true accuracy of the pendulum?
Todd E

Jon A: If Newton had shot the ballistic pendulum with the same 12 guage as that cop in the "Overkill" thread, I guess the pendulum would have been blown completely out of the window (and knocked over a truck on the street outside).

Thanks again for bringing a little enlightenment.

Jon A,

Could you or one of the others with knowledge please provide teh equation that is used to calculate the projectiles velocity due to the impact with the pendulum?

Thanks,
Todd E

Todd E, you rely on the fact that torque (Force x distance) and energy have the same units. Measure the distance from the hinge of a steel plate to the impact point. Measure the angle or height of the plate (pendulum) from impact. You can relate the height of the swing to the applied force (sorry, I don't have a text with me and my brain is too tired to start with F = ma). There are basic equations in any freshman physics text for a simple pendulum. Knowing the force and distance (moment arm) you calculate the bullet's kinetic energy: KE = F x d. Knowing the KE, you get velocity.

Now, all of this is not perfectly correct. The assumption is that no energy is lost in resistive forces, or deformation of the plate and bullet, and that all of the velocity of the bullet is spent on impact, etc. Well, those things don't go together. But in some circumstances it is close to the right answer.

v = ((m1 + m2)/m1)*(2*g*h)^.5

m1 = mass of bullet
m2 = mass of pendulum
g = acceleration of gravity
h = height the pendulum reaches

Ummmm... I think it is a little simpler than all that, Harald... When I was learning physics a zillion years ago, good ol' Dr. Dibble would bring in a ballistic pendulum and an ancient .22, and proceed to demonstrate.

The pendulum is just a horizontal 4x4 piece of lumber, with a support string at each end. As it swings, it rises, but remains parallel to the earth. You set a meter stick up underneath it, with a little paper slider, cut to fit around the meter stick. You angle the meter stick up slightly, so that as you fire a bullet into the end of the lumber, the motion of the pendulum slides the slider. So you know how much height the pendulum gained, and thus the potential energy.

The big assumption in all this is that the amount of energy lost to shredding wood and deforming the bullet is small compared to the whole kinetic energy.

Year after year, CCI MiniMags were the most consistent and potent .22 ammo.

Jon A and I are in violent agreement... and were apparently typing at the same time!

Between the Robbins pendulum (which we used at the university, back in the Jurassic Period!) and the modern electronic chronograph, there was the ingenious electromechanical le Boulang� chronograph. This device held a long steel rod (with a soot-blackened aluminum jacket or sleeve) suspended vertical by a magnet.

Before each shot, the operator tripped a solenoid that jabbed a blade into the side of the jacket around the rod. As the bullet broke a fine wire (usually about 3 ft in front of the muzzle), the magnet released the rod. As it fell, the bullet struck a dangler that triggered the solenoid, and the solenoid jabbed the blade into the falling rod's jacket again. The distance between the knife marks, subjected to the appropriate math and physics, told the bullet's average velocity between the solenoid's two triggers.

A well made pendulum was large and tedious to use -- keeping the weight of the bob constant was both necessary and a pain -- and the bob had to be prepared for each shot. The le Boulang� chronograph was less clumsy and easier to use than the Robbins pendulum but MUCH more complicated to use than any of the modern electronic marvels.

The Potter and later the Avtron, two of the earliest electronic chronographs, were great improvements over the le Boulang� but not nearly so convenient and easy to use as, say, an Oehler Model 35P. I have a couple of the old Avtrons and will display them at the Powley Center -- would probably use 'em for some tests, if I could get 'em refurbished. One uses a pair of break screens, the other a pair of make screens.

As clumsy as they all were, all these predecessors of the Oehler 35P were amazingly accurate. Their operating principles relied on some pretty reliable, pretty well known laws of physics.

"When I was learning physics a zillion years ago, good ol' Dr. Dibble would bring in a ballistic pendulum and an ancient .22, and proceed to demonstrate.
"The pendulum is just a horizontal 4x4 piece of lumber, with a support string at each end. As it swings, it rises, but remains parallel to the earth. You set a meter stick up underneath it, with a little paper slider, cut to fit around the meter stick. You angle the meter stick up slightly, so that as you fire a bullet into the end of the lumber, the motion of the pendulum slides the slider. So you know how much height the pendulum gained, and thus the potential energy."

That was an extremely crude imitation of a good Robbins pendulum. The bob on a Robbins used for serious work was a long section of large tubing (filled with sand, sawdust, etc) with a pair of suspension wires on each end and knife-edge bearings on the ends of the suspension wires. Boxes of bullets atop the bob let the operator remove, for example, a 180-grain bullet for each 180-grain bullet just fired into the bob. From time to time, the bob had to be cleaned-out, refilled, and precisely weighed again. The spent bullets came out, and the boxes atop the bob got a new supply of bullets.

The physics-lab pendulum you describe was no more than an educational toy in comparison with "the real thing." It's not my intent to demean it -- only to point out that a full-scale, well built, properly used Robbins was not nearly so crude.

V^ = U^ + 2as

V = Final velocity of pendulum which will be 0

U = Initial velocity of pendulum

a = acceleration of gravity

s = height pendulum achieved.

Thus we will know U, which was the initial velocity given to pendulum.

Then it is simple as the momentum of the pendulum is the same as the bullet.

If the pendulum is 1000 times heavier than the bullet, then the bullets impact velocity will be 1000 times the pendulums initial velocity.

Did I pass

Mike