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Old February 23, 2011, 10:50 PM   #1
ClemBert
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Non-symmetric BP flame?

You are looking at an Uberti Walker sitting in a test fixture that is used to evaluate test firing certain cartridges. This Walker was converted to fire the .45 BPM cartridge. The question is: Why is the flame non-symmetric? Notice how the flame jets out downward. Discuss...

Sorry for the poor quality of the picture. It was taken from a camcorder on a bright sunny day with the sun at its highest point.



The .45 BPM cartridge being fired contains 55 grains of Goex FFFg, a fiber wad, and a 150 grain Biglube bullet (second from the right). That's a .45 Colt on the left side.


Last edited by ClemBert; February 27, 2011 at 10:54 AM.
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Old February 23, 2011, 11:25 PM   #2
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I can't answer you, but let me share a related observation. I loaded the Walker up with 50 grains of Triple Seven and a .457 ball this evening. All chambers had this load. 4 chambers had a considerable fireball and 2 had none visible. I can't explain it. They all behaved the same except for the fire.
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Old February 24, 2011, 07:05 AM   #3
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If that's the only picture you have (that is, only one shot was photographed), I'd say the result is just random. Burning gas is a plasma, so where it goes in free atmospheric space is subject to chaos theory.
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Old February 24, 2011, 07:10 AM   #4
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I might add

I comparison of the Walker fireball with that of other revolvers might be instructional.
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Old February 24, 2011, 08:48 AM   #5
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Just a guess, but does the fixture holding the Walker move under recoil? It might be the fixture and or gun rising up a little bit under recoil. Again just a dumb guess
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Old February 24, 2011, 09:23 AM   #6
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S.W.A.G. only but...........
Unburnt powder grains exit muzzle, curve down by gravity & get ignited by muzzle flash?
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Old February 24, 2011, 10:26 AM   #7
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Quote:
Originally Posted by mykeal
If that's the only picture you have (that is, only one shot was photographed), I'd say the result is just random. Burning gas is a plasma, so where it goes in free atmospheric space is subject to chaos theory.
I have some other film footage to analyze yet...different cartridge combinations.

I will say that it was a rather breezy day (15 mph) so your theory is quite plausible.
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Old February 24, 2011, 10:28 AM   #8
ClemBert
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Quote:
Originally Posted by olmontanaboy
Just a guess, but does the fixture holding the Walker move under recoil? It might be the fixture and or gun rising up a little bit under recoil. Again just a dumb guess
Yeah, the test fixture does recoil. You can see the slides under the top platform and a gas piston in the back. I can tell from the picture that the bullet has clearly exited already (because of the flame) and based on the position of the top platform I can see that the firearm has not recoiled yet.
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Old February 24, 2011, 10:31 AM   #9
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Quote:
Originally Posted by wogpotter
S.W.A.G. only but...........
Unburnt powder grains exit muzzle, curve down by gravity & get ignited by muzzle flash?
I had thought of that too but I just don't think there is enough time for gravity to have taken its effect on any loose powder. Just a thought. I need to experiment with different amounts of crimping around the bullet to see what effect, if any, it would have.
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Old February 24, 2011, 11:04 AM   #10
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It may have something to do with the distribution of unburned powder within the barrel. Just a thought, but perhaps the powder charge was not uniformly compressed, so maybe there would be some non-uniformity in the muzzle flash.

I agree with ClemBert - gravity will not have that much effect within that short of time.
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Old February 24, 2011, 12:15 PM   #11
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I think that what's seen in the photo is totally normal. It resembles the downward draft behind a large aircraft that's airborne. Behind it there's a vortice of downward turbulence, a downward wake of circulating air that lasts for a period of time.
It's simply an air circulation pattern that originates from the bullet surface creating an obstacle to the air flowing around it as it travels at high speed when exiting the barrel tube.
I believe that some of the relevant concepts involved are vortex (or vortice), airfoils and airflow, Bernoulli's Principle, and the venturi effect.
What I've read points to this downward airflow as being normal.
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Old February 24, 2011, 12:42 PM   #12
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Quote:
I just don't think there is enough time for gravity to have taken its effect on any loose powder.
Funnily enough I just saw a show on NatGeo where they had a 15-man squad of musket firers competing against a Gatling.

Every time the Gatling fired there were sparks arcing down just as your pic shows but they had a faster capture speed so you could see a storm of individual burning grains all dropping & stopping withing 10~15" of the muzzle.

I guess the individual grains don't have the mass to keep going like a bullet or ball?
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Old February 24, 2011, 12:58 PM   #13
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What you are seeing may be an artifact of the camera. If it is older, or recording at a simulated high resolution, it will be scanning from the top down, so there is a time difference between the top and bottom of the picture. If you can try recording at a lower resolution and 60 frames per second.
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Old February 24, 2011, 01:23 PM   #14
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Quote:
I believe that some of the relevant concepts involved are vortex (or vortice), airfoils and airflow, Bernoulli's Principle, and the venturi effect.
What I've read points to this downward airflow as being normal.
Somewhere, someplace, a dissertation is waiting to be written
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Old February 24, 2011, 09:53 PM   #15
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I just looked at the specs on the video recorder: 60 fps @ 1280x720.
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Old February 25, 2011, 02:52 PM   #16
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OK 720@60Hz is newer and it is not an artifact of the camera.
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