"Wake Turbulence"

oooops......again


TWO effects here.... I just need to shut up........ "bumpy air" from a dead calm condition is entirely another subject from "wake turbulance."

Let's just settle my sauce by saying I have NO FRIGGIN' OPINION on the actual subject at hand of wake turbulence.

sorry

al
 
I did a little internet search on the subject, and came up with this, seemingly knowledgeable response.

"Many large caliber cannons use what is called an initiator to help get the Smokeless powder burning. The very large grains of extruded powder used in large caliber artillery shells are a bit more difficult to ignite than the types of powders we use in small arms. So a Black Powder initiator is often used, because Black Powder is very easy to ignite. In self contained artillery shells, the initiator is often a perforated tube running up the center of the 'cartridge'. The tube is filled with Black Powder, or some other highly volatile material. When the primer of the shell is struck, it ignites the initiator, which in turn ignites the main charge.

The Navy's 16" guns use 40 pound bags of extruded stick powder. The individual grains are almost as large around as a pencil. Since this powder is relatively difficult to ignite, the last bag in the stack has a pouch filled with Black Powder sewn at the rear. The normal charge for the Navy's 16" guns is four forty pound bags of powder. The bags are made of silk, so they completely combust in the gun. The shell is rammed into place by a mechanical ram, then the bags of powder are placed on the ram and gently shoved into the breech. Bad things can happen if they are rammed in too quickly. The last bag has the BP initiator at the rear. The actual primer used to fire these guns is about the size of a 38 Special cartridge. When the primer is struck, it ignites the Black Powder first, which then ignites the 160 pounds of Smokeless.

One of the reasons Goex is still in business is they are the only supplier of Black Powder made in the USA. Remember, BP is not just used in the 16" Naval guns, smaller shells have a BP initiator in them too."
 
Two types of turbulence

If you watch the video in post#12, you can see how vortices can travel pretty long distances, at least in this video. If these vortices are being produced by high velocity gasses,you can imagine how they would disturb the air in front of the bench.

As far as mirage(Image) being the culprit. I just bought a Rail Gun. When I shot it in dead calm conditions,I got the same results on many occasions. If your flags ain't moving,you can't see whats out in front of you. If you can't see it, you can't hold for it.

Hurry up with that project Andy.



Glenn

There are two types of turbulence at play. The first is that produced by the expanding muzzle gasses. They continue to expand after they are released from the barrel and as Glenn states do travel quite some distance down range. The second is the turbulence produced by the bullet itself. Only small in magnitude but when overlapped by several shooting at once can cause bullets to cant just as the wind does. Depending on how well a bullet is stabilized a small amount of wind or turbulence can disrupt a bullet more in proportion to its strength than a good gust. In some cases it induces a wobble that may be corrected due to energy dispersion after it passes say the 150 yard mark but can make a mess of the target at 100 yards.
This is why I am keen to build a prototype interferometer to see all these things. In the mean time bring on some wind. Not a gale but enough to wash the range clean of mirage, muzzle gases, poltergeists and the like.
Andy
 
gross example of what happens on an orders of magnitude smaller basis in our game. Which Battleship?Remember, these barrels are eating black powder, not smokeless

David


Which Battleship?.....Your guess is as good as mine David. I got it from a photo album. That gun looks more like a 5 inch to me.


Glenn
 
A handy explanation, for sure

I've been shooting bench rest for a bit over two years. I thought I had discovered, and eliminated, about all the reasons to shoot a 249 in IBS Score. At my last match, on the second target for score, I had 4 X's and a 9. I was inside waiting for my target to come up on the wall so I could get my crying over with. The guy scoring my target noted that I had been clean up to that point. He is one of our most experienced shooters. He asked, "was it dead calm?" I said that yes, in fact it was. Then he explained about the wake vortex, and how you need to watch the shooters on either side of you during a dead calm. First I had ever heard of that, and I will never forget it. That may not be the reason for my one errant shot that match, but it made me feel better to have a possible explanation that I could adjust for. I personally favor the "still mirage" explanation rather than the effect of moving air.
 
Non believers

I personally favor the "still mirage" explanation rather than the effect of moving air.

I guess it doesn't matter how much evidence on the subject is gathered there will always be non believers no matter what the subject is. I still meet people at the range who believe that their bullets travel so quickly that wind doesn't have time to affect them.
Andy.
 
I would have to conclude that if rail guns experience the problem, that this pretty much rules out mirage.

If the pressure of a crosswind causes bullets to cant slightly in to or away from (pick one)the direction that the wind is coming from, could it be that without any wind, that the motion of the bullet stays more random (at the distances that we shoot at), sort of semi-spit balling to the target, and could the balance and shape have something to do with the degree to which this happens? Has this been observed equally at 100 and 200 yards?
 
All of the above

I would have to conclude that if rail guns experience the problem, that this pretty much rules out mirage.

If the pressure of a crosswind causes bullets to cant slightly in to or away from (pick one)the direction that the wind is coming from, could it be that without any wind, that the motion of the bullet stays more random (at the distances that we shoot at), sort of semi-spit balling to the target, and could the balance and shape have something to do with the degree to which this happens? Has this been observed equally at 100 and 200 yards?

Actually if you have ever seen extreme high speed images of bullets leaving a muzzle you will see the gasses which are travelling faster than the bullet over take it for a short distance. That gas cloud will hit the bullet up the backside and if the muzzle blast is affected by a slight cross wind will not hit the bullet in the butt uniformly canting it. Turbulence will do the same thing. In fact the number of intervening variables that can and will disrupt a bullets flight path are so many in number not to mention the balance and shape of the bullet itself I can say confidently to your question. All of the above.
Andy.
 
Houston Warehouse

This is all very fascinating, but I'm still having trouble with the thought of vortexes in calm air being a major contributor to big groups. The reason I say that is because of the Houston Warehouse results. I've read and re-read an article by Dave Scott where it states pretty clearly that there was "no wind or mirage" in the warehouse and that the gases, etc., simply floated up and away in the huge building. Here's a quote:

“The shooting would generally start about 10 at night,” he began. “Everything settled down, and the air got real still. It just felt right. Then it was like shooting outside, except there was no wind or mirage. If you had a rifle that would shoot, it would shoot. If you didn’t, you found out pretty soon that you had a problem.”

A unique feature of the Houston Warehouse was the fact that it indeed had similarities to shooting outside. Unlike shooting tunnels, where the shooter must wait between shots for powder gases and heat to clear, firing in the vast expanses of the warehouse could be conducted at any pace. The offending products of combustion rapidly floated to the roof, high above.

So, given that, I'm at a loss for why still air OUTSIDE is so bad compared to still air INSIDE.:confused:
And it's even more confusing when you consider that Virgil could consistently shoot 0.030" groups!

Dennis
 
Non-Believers, Warehouse Shooting

Let me say first, Andy, that I never said that air couldn't move a bullet or that vortexes weren't a part of it. If I was that clueless, I wouldn't have lasted even 2 years in bench rest. I just personally believe that percentage-wise, it is more likely for your particular bullet to be affected in a shoot in calm conditions by the mirage from all those hot gasses belching out than from a particular vortex. I think both factors can be in play.

Now as to mirage in warehouses, I spoke with Ralph Council personally about a year ago. I am quoting as nearly as I can (I wrote this down as he said it) "We had to keep a fan going, or we got squirrelly mirage." Ralph said he was in on a lot of all-nighters in the Houston Warehouse and that he mostly did loading, helped out and observed technique.

I have not personally shot in a warehouse or tunnel, but I have read that it is common to get "still mirage" in tunnels, where there is a shift in the apparent position of the target, but no wavy lines to give it away. I have also read that it sometimes happens outdoors too, perhaps due to two layers of air with different temperatures. I suspect that effect can be the cause of some unexplained jumps in vertical that I have seen people experience in matches. If your neighbor's column of heated air from his last shot drifted over in front of you, you might get shift from that "still mirage". I think that "wavy mirage" comes off the ground being heated by the sun.
 
One little experiment that could be done quite easily, given the close focus capability of March scopes, is to use a close aiming point that is narrow enough to let the bullet pass it, so that paper is punched and groups formed at standard distances. It seems to me that this might help minimize the effect of mirage, whatever the type.
 
I have read on this very forum of all the hazards relating to causes of large groups and low scores. After reading this thread and consulting with my own team of experts I have come to the conclusion that the breeze from the wings of a gnit on the gnut of a gnat will influence the flight of the bullet.



Francis...I use Bug Spray for the gnits and gnats:D
 
One little experiment that could be done quite easily, given the close focus capability of March scopes, is to use a close aiming point that is narrow enough to let the bullet pass it, so that paper is punched and groups formed at standard distances. It seems to me that this might help minimize the effect of mirage, whatever the type.


Lower scope power significantly reduces the effect of mirage. A Rail Gun eliminates the effect unless you need to look through your scope to make an aim point adjustment.




Glenn
 
Now as to mirage in warehouses, I spoke with Ralph Council personally about a year ago. I am quoting as nearly as I can (I wrote this down as he said it) "We had to keep a fan going, or we got squirrelly mirage." Ralph said he was in on a lot of all-nighters in the Houston Warehouse and that he mostly did loading, helped out and observed technique. QUOTE]

Here's what the article said about the fan; it was carefully adjusted to blow over the barrel, but not over the muzzle:

"Finally, in a bold stroke of technological innovation, Bob brought in a small electric fan. Carefully directed over the barrel, the puny appliance effectively cleared away the barrel mirage. Care was exercised, however, not to allow errant air movement to invade the sensitive muzzle area and thereby deflect the bullet from its true path"

So, I'm still confused, but on a much higher plane!

Dennis
 
"Warehouses"

I used to shoot RimFire benchrest. To me,its tougher than shooting Center fire. For several season's,during Fall/Winter,there were indoor Rim Fire shoots held in a Warehouse near Ennis,Tx. I visited a couple of these shoots just to watch. The first thing I noticed was,there were several shooters using wind flags, inside the warehouse. This warehouse was a solid well constructed facility. I asked one of the competitors why was it necessary to use wind flags. His response was that there was "Stuff moving around in the warehouse that he needed to see. These guys shoot sub sonic ammo. As I recall,there were six to eight benches set up for the shoot. I can't prove it,but I suspect that the stuff that was moving around in that warehouse was caused by "Wake Turbulence" from sub sonic ammo.




Glenn
 
I've tried my hand at 22LR benchrest - unofficially - and it's tough! Good wind training, but still really tough to get those little pills to go where they should!

After reading all the Houston Warehouse information, and Virgil's ability to get consistent 0.030" groups, I'm wondering what's the point? Michael Stinnett just shot a 0.0077" group, 1/4 the size of Virgil's, and he was outside! Has he discovered how to read the unreadable? Vortices, gnits, gnats, gnuts, PFM, or????

Dennis
 
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