Gas sealing with PRBs in rifled barrels

[Wes/Tex]

Excellent photos, thank you. Those are 'light years' ahead of what we got all those years ago. It truly amazes me at what can be seen in quality high-speed photography. Thanks again! :hatsoff:

 

[Rifleman1776]

Fascinating. My admiration for your work is unbounded. :bow:
But :shocked2: that doesn't mean I necessarily agree with you. We are looking at the same pic but seeing different things. What the pics show is not the flame proceeding out of the muzzle ahead of the ball. What we are seeing is the burning detrius flying faster than the ball after both have left the muzzle.
Jug is to you again. :stir:

 

[coloradoclyde]

didn't I mention something about the velocity of the explosion? it is always greater than the velocity of the projectile I'm not that good at phsysics but I think that might be Newtons 3rd law

 

[Larry Pletcher]

The devil is in the details while setting up the shot. The flash is shut down to 1/40,000 sec. The camera shutter is set to stay open for a couple seconds. The room is dark. when the rifle is fired and the ball breaks an infrared beam the flash is triggered. The ball or anything that does not make its own light, is only seen during the flash duration. The sparks however, make their own light and can be seen during the time the camera shutter is open. If the sparks were only seen during the flash, they would be stopped as well. But, with the shutter open for seconds, the sparks can be seen after the flash duration is over.

In reality the process goes like this. The shooter gets his sight picture on the bench. The aim has to be repeatable to hit the infrared beam. (That is set up prior to the shot.) With the shooter ready, I shut off the room lights and open the camera shutter. The shooter fires the shot, and we wait for the camera lens to close. Then lights are on and we look at the shot. If necessary we repeat with slight adjustments. Usually that means many repeats.

I hope get set up for more shots in before Christmas. I'll get some shots of the equipment.

Regards,
Pletch

 

[Billnpatti]

Uh......What kind of glass? and where are you going to do this experiment? Just want to know so I can be far, far away. :haha:

 

[Billnpatti]

I was thinking about your explanation of how the shadow of the spark could occur after the ball had already exited the scene. I thought I understood what you were saying and agreed with the possibility. However, after giving it some thought, I wanted to toss out this idea: When the flash goes off and captures the ball in flight, its image is already fixed in the digital media. Then if a spark flies by after the ball leaves the picture, the spark will not leave a shadow. It may leave an orange streak of light superimposed on the image of the ball but it will not create a shadow where one did not exist because the image of the ball is already fixed. Does this make sense or am I off on another tangent?

 

[Claude Mathis]

What the pics show is not the flame proceeding out of the muzzle ahead of the ball. What we are seeing is the burning detrius flying faster than the ball after both have left the muzzle.

My thought as well.

 

[Zonie]

Then if a spark flies by after the ball leaves the picture, the spark will not leave a shadow.

I totally agree.

Had the spark flown past after the ball had left the image there would be no ball present for the shadow to land on.

IMO, the shadow was caused by the spark, traveling at a much faster speed than the ball, blocking off the light from the flash.
This created the shadow that clearly shows on the side of the ball.

 

[coloradoclyde]

http://en.wikipedia.org/wiki/Internal_ballistics

read it explains all

 

[coloradoclyde]

There are many processes that are significant. The source of energy is the burning propellant. It generates hot gases that raise the chamber pressure. That pressure pushes on the base of the projectile, and causes the projectile to accelerate. The chamber pressure depends on many factors. The amount of propellant that has burned, the temperature of the gases, and the volume of the chamber. The burn rate of the propellant depends not only on the chemical make up, but also on the shape of the propellant grains. The temperature depends not only on the energy released, but also the heat lost to the sides of the barrel and chamber. The volume of the chamber is continuously changing: as the propellant burns, there is more volume for the gas to occupy. As the projectile travels down the barrel, the volume behind the projectile also increases.

There are still other effects. Some energy is lost in deforming the projectile and causing it to spin. There are also frictional losses between the projectile and the barrel. The projectile, as it travels down the barrel, compresses the air in front of it.

 

There are many processes that are significant. The source of energy is the burning propellant. It generates hot gases that raise the chamber pressure. That pressure pushes on the base of the projectile, and causes the projectile to accelerate. The chamber pressure depends on many factors. The amount of propellant that has burned, the temperature of the gases, and the volume of the chamber. The burn rate of the propellant depends not only on the chemical make up, but also on the shape of the propellant grains. The temperature depends not only on the energy released, but also the heat lost to the sides of the barrel and chamber. The volume of the chamber is continuously changing: as the propellant burns, there is more volume for the gas to occupy. As the projectile travels down the barrel, the volume behind the projectile also increases.

There are still other effects. Some energy is lost in deforming the projectile and causing it to spin. There are also frictional losses between the projectile and the barrel. The projectile, as it travels down the barrel, compresses the air in front of it.

And what's your conclusion after you read all that online?

 

[coloradoclyde]

some people are wrong and everyone is right.
and this forum needs an internal and probably a external balistician

 

[coloradoclyde]

science is history too!
If a picture is worth a thousand words, why do we usually come to a singular conclusion?

 

[coloradoclyde]

more fodder http://en.wikipedia.org/wiki/Transitional_ballistics

 

[Larry Pletcher]

I was thinking about your explanation of how the shadow of the spark could occur after the ball had already exited the scene. I thought I understood what you were saying and agreed with the possibility. However, after giving it some thought, I wanted to toss out this idea: When the flash goes off and captures the ball in flight, its image is already fixed in the digital media. Then if a spark flies by after the ball leaves the picture, the spark will not leave a shadow. It may leave an orange streak of light superimposed on the image of the ball but it will not create a shadow where one did not exist because the image of the ball is already fixed. Does this make sense or am I off on another tangent?

Bill, I think you're right. I've gone back and forth on this. I first thought the spark was passing the ball right in front of the camera. THen I considered that the extra time the lens is open may be fooling me. The shadow is the exciting thing in the pic - or troubling depending on your thinking.

I don't doubt that the sparks can be moving faster than the ball as Claude says. The shadow left by the spark seems to say the ball and the spark must be there at the same time. I have one other pic with a spark shadow, but it's not in good focus. At least the shadow isn't a single happening.

Regards,
Pletch

 

[ApprenticeBuilder]

I would think that if there was flame escaping the patch then the patch would be charred/shredded beyond the centerline of the ball.

I am not so sure. You can pass your hand thru a candle flame without getting burned as long as you move it fast enough. The patch is only in contact with the burning powder/hot gasses for an instant, not long enough to burn thru the bottom (center) of the patch. Easy enough to experiment by shooting a very loose patch/ball combo (loose enough to guarantee blow by) & see what the recovered patches look like. Inquiring minds want to know ..............

For the passing of the hand thru the flame to be relevant the flame needs to be at pressures such as expanding gasses propelling a projectile out of the bore of a fired weapon otherwise we are comparing apples to door locks.

Agreed that the patch is only in contact with the expanding gasses for a fraction of a moment but it is a most violent meeting.


I agree about the loose combo to test out the durability of the patch material, there have been several posts that advocate adding wads or fillers to compensate for the shredded patches so as to allow for ease of loading etc. instead of using a larger ball or thicker patch which typicaly requires much more effort to load.

The following picture shows how a tight patch/ball combination can force the soft lead to form to the grooves and lands leaving an imprint of the material weave in the soft lead, in a Green Mountain 50 cal. barrel I am loading a .495 ball with a .026 denim patch, no way to ignore the imprint on the ball.

Also with that thickness of patching there is no possible way to "see thru" the heavy denim.

 

[Rifleman1776]

I think the jug is empty.
Bye. :v

 

[Brad Clark]

They were called polypatch and were great, never expeirenced them coming loose but could happen.

I just started looking for them, having been out of the sport for many years. I'm gathering my stuff to prepare for this year and wanted to get some supplies - my beloved green .50 cal polypatches. I converted to them after many attempts for accuracy with regular cotton patches that would not group. I switched and can group with a 3 or 4 " circle at 100 yards pretty regular, back a few years ago I should say. I'm sorry to see them unavailable and even dissed. I loved them. Never had a bit of a problem. So much easier to start than cloth. Anyways, keep the wind in yur face N the sun at yur back