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  #11  
Old 01-26-2010, 09:13 AM
edlmann edlmann is offline
 
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Originally Posted by VMFn542bob View Post
I haven't a clue how they would have measured velocity back then, when those old MANN barrels in the photo were tested.
Back before the development of the modern chronograph, I believe velocity was tested by firing a projectile at a swinging pendulum of a known weight at a known distance. High speed photography would measure how far the pendulum was moved and the velocity computed from that.

Prior to Oehler's chronograph, a lot of inaccurate velocity estimates were in print.
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  #12  
Old 01-26-2010, 06:34 PM
UncleWilly UncleWilly is offline
 
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I've seen pictures of those old pendulums. They predate high speed photography. The pendulum moved a very light weight indicator needle around a dial and when the pendulum fell back, the needle stayed at its maximum moved location. Pretty clever device. If everything was weighed and measured accurately, some standard physics equations would yield the velocity.
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  #13  
Old 01-27-2010, 12:37 AM
americal71 americal71 is offline
 
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Perhaps I can shed a very little light on the subject. Every lot of military ammunition had to meet accuracy requirements to be accepted. For example, M118 7.62 Match ammunition had to produce a 3.5 " mean radius at 600 yards. Samples from each lot were sent to a testing facility - at various times this could have been Frankford Arsenal, RIA, APG, etc. At some point the manufacturing facilitiies were required to have their own test set up. I believe as late as the '50's and '60's the Govt had personnel stationed on sight (military or civilian) to observe and certify the results. As you see in those old photos at an early time they actually tested at the required range. Later they built tunnels to limit the effect of wind and climate and fired the ammunition using the Mann devices as a known constant test bed at 100yds/m and extrapolated the results. The number of test required resulted in a large number of the devices and the barrels being manufactured. I know that SA, FA, and later RIA manufactured most of the barrels.
When I was at RIA in the '70's Rodman Lab still had Mann devices that could be mounted into a machine rest with a large armor shield that were used in ammunition development. The only test I witnessed using these devices was in development of the projectile profile for the 6mm SAW cartridge. Shortly after that, the lab was closed down and the equipment and mission transferred to Picatinny Arsenal. Hope this may help!
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  #14  
Old 01-29-2010, 09:23 AM
VMFn542bob VMFn542bob is offline
 
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Originally Posted by americal71 View Post
... Hope this may help!
Sure helps me and confims what I suspected. It makes a lot of sense to shoot through a tunnel. Not only can wind effect be eliminated the entire environment can be controlled inside a tunnel: altitude, humidity, temperature etc, about every variable that can affect the performance of the bullet. With the design of the MANN barrel reducing its effect on the bullet to the maximum extent possible, and the tunnel controlling the environment, the only variable left is the ammunition. That would seem to imply that group width would be then be related to the projectile and group height would be related to the velocity. Because many things can affect velocity that is probably where ammo manufacturers concentrate their attention.
A little trivia: I have read that the performance of the black powder 45-70 GOVT cartridge was so bad that the shape of the bullseye was changed to accept the fact that velocity could not be controlled well enough to shoot at a round bullseye. As a result, the military competition target was changed from a round bullseye to a bullseye that was about twice as high as it was wide.
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  #15  
Old 01-31-2010, 12:41 AM
VMFn542bob VMFn542bob is offline
 
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Default More information on the MANN Accuracy Device

Here is another photo of the MANN Accuracy barrel in early field testing. This photo and the earlier photo in this thread was found linked to this on-line document:
http://www.nps.gov/spar/historycultu...erimenting.htm The following statement there describes the purpose of this device.
"Mann Accuracy Barrel SPAR3728 This barrel is as close to being perfectly accurate as it was possible to achieve. It is used to test the performance of ammunition. Rounds are fired under conditions of controlled temperature, pressure, humidity, and wind. If the ammunition is consistent and the bullet perfect, each round would hit the same point on the target. The Mann barrel was used in testing the T65E5 cartridge, which became the standard NATO round."

This photo clearly shows the two precision "donut" bearings attached to the barrel of the Mann Accuracy Device. It also does not have the "collar" attached to the receiver end of the barrel that appear on later MANN "rifles".
The MANN Accuracy Device is laying on a elaborate test platform with a "V" way with compound adjustments.
The stock has not been cut off, possibly because the design of this platform does not make that necessary.
The MANN "rifle" is not yet positioned in a in a battery position so there is no way of knowing the orientation of the barrel when it was fired.

With the exception to handguns, as far as I know, no receiver has ever been designed to support the weight of a rifle barrel, much less the massive barrel on the Mann Accuracy Device.
Accurizing most rifles require bedding the rifle barrel and receiver. I think that two bearings shown in the field test photos accomplish the same thing.

I also think that if the barrel is supported only at he breech end by that collar, the barrel is floating.
Battleship rifles are supported at only one end and have changes in barrel diameter and tremendous accuracy.


In the case of the currently available barrels, which have a precision collar at the receiver end, the collar can support the weight of the barrel without introducing any stress on the receiver or the gun stock.

TORQUE- When a bullet is fired through a rifled barrel, the rifling must rotate the projectile almost INSTANTLY.
The projectile will pass some of its rotating energy to the barrel causing the barrel to twist (torque).
A wave of energy will be pass down the barrel from the receiver to the muzzle.
I believe those different diameters on my MANN barrels are intended to disrupt that wave before the projectile gets to the muzzle and minimize the effect on accuracy.

Just how much torque is this? The 308 Winchester / 7.62x51 NATO M1A rifle has a muzzle velocity of 2820 feet per second.
The M1A barrel (and the MANN barrel) has a 1 turn in 10 inch twist on the rifling. The length of the M1A rifle barrel is 22 inches.
Doing the math, the unfired bullet sits inside the cartridge, rotating at ZERO revolutions per minute (RPM).
Pull the trigger.
When the bullet exits the muzzle, just 22 inches of travel, it is rotating at about 164,000 RPM.
That kind of torque would rip out your transmission and break you car all over.

Another early Mann barrel testing photo


I don't know how long it may be before I will have the time to test the two MANN barrels I have.
When I do have the time this drawing shows how I plan to support them.
Anyone wishing to use this idea, or any variation of it, has my permission to do so.
I do not think there will ever be any more MANN Accuracy Devices like this made.
I feel sure that advances in technology provide other, easier and more accurate methods for measuring the performance of ammunition and weapons.

A plan to support the MANN Accuracy Device by the collar.
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  #16  
Old 03-18-2010, 07:05 PM
mousegun mousegun is offline
 
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Quote:
Originally Posted by edlmann View Post
Back before the development of the modern chronograph, I believe velocity was tested by firing a projectile at a swinging pendulum of a known weight at a known distance. High speed photography would measure how far the pendulum was moved and the velocity computed from that.

Prior to Oehler's chronograph, a lot of inaccurate velocity estimates were in print.
The ballistic pendulum went out of serious use at armories over a hundred years ago. Instrumental velocities in the time of John Garand were quite accurate and reliable if not tedious to measure. According to Hatcher's Notebook on page 251 service ammunition was measured with a Le Boulongé chronograph. The setup and method of measuring instrumental velocities with the chronograph is described on page 404.

A typical chronometric measurement around the turn of the century was probably made with an electromechanical apparatus consisting of frangible detector screens, a source of high voltage and a recording device. The recording device was usually a hysteresis/synchronous motor driving a waxed disk with a conductive backing on a spindle. A worm grear drove a stylus in a spiral track on the disk. High voltage (90-200V) was connected across the fragible screens and the leads connected to the stylus through a "kicking" inductor. As the bullet passed through the screens the short caused a high voltage spike on the stylus to arc through the disk. The angular distance on the disk between two arc spots indicated time of flight. Very accurate...

..and expensive.
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Last edited by mousegun; 03-18-2010 at 07:15 PM.
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