I don’t pretend to know the answer to this so it’s not a “gotchaâ€...but has anyone ever pondered what the effect of draft/turbulence behind a bullet has on rounds fired from a high cyclic rate automatic weapon?

Anyone who has ever fired a fully automatic rifle with tracers knows that the bullets are pretty close to each other and it is logical to assume that there would be some effect going on with the bullets traveling through the “wake†of the bullet ahead of it.

I do not recall ever reading anything regarding this topic.

Still, considering a muzzle velocity of 2700 fps @ a cyclic rate of 3 shots per sec., would imply that there would be 900 ft between bullets, or 300 yds.

I would hardly believe that residual turbulance from the previous bullet would have any effect, unless the bullets were following each other, say at a 50 ft distance between shots.

That would require a cyclic rate of 54 shots per second. I know of no full auto rifle that could fire that fast.

I have no idea either, Mike...but when you get older you start pondering all sorts of weird things that make absolutely no difference to anything at all!

I’ll add to the brain teaser.

What about a minigun firing at 6,000 rpm (100 rounds per second)?

quote:

Originally posted by Rick 0311:
I’ll add to the brain teaser.

What about a minigun firing at 6,000 rpm (100 rounds per second)?

Well, I would contend that it would require too much reloading and barrel cleaning!!!

I would also have to believe, if the gun is held steady enough so the bullets are following in the previous bullets path, that the turbulence would have to affect the grouping of a string of shots.

Which is a really big "if".

I don't know either, but with the (DANG! Forgot the name...) 20 m/m cannon you appear to get a definite "cone" of fire, from the six barrels. That suggests at least 6 different bullet paths, with 16.6 rps per path at best, no matter how steadily held..

Still, would be interesting to know if the "drafting"of each bullet behind the one in front of it would eventually result in the "behinder" bullets catching the leading ones which were being more slowed due to air resistance? (Assuming a gun which WOULD fire 55 or so RPS from a single barrel...)

Probably not, but an interesting theoretical question......

P.S.,remembered the name..."Vulcan"

The miniguns have multiple barrels but they fire from the same position as they rotate around the central axis, so in effect the bullets are all leaving the bore at the same indexed position(just like a Gattling Gun) as the previous barrel that fired and should therefore be “following†each other.

Obviously, since the aircraft is also moving there would be a dispersion, but what if the weapon was fired from a solid stationary platform????

quote:

Originally posted by Rick 0311:
The miniguns have multiple barrels but they fire from the same position as they rotate around the central axis, so in effect the bullets are all leaving the bore at the same indexed position(just like a Gattling Gun) as the previous barrel that fired and should therefore be “following†each other.

Obviously, since the aircraft is also moving there would be a dispersion, but what if the weapon was fired from a solid stationary platform????

When following a tractor trailor on the highway, turbulance begins effecting my vehicle at about 40 ft. seperation. now that's a real loose estimate, but it should be close enough for our purposes here. Drafting begins to occur when I get within 20 ft.

Does the increased speed of a bullet create a "longer" turbulance trail, or is the length of the turbulance trail a constant, regardless of projectile speed?

I haven’t got the slightest fu*king idea!!!

Once we get this one solved we can get into what happens to bullets fired out the rear of a plane flying at Mach 2?????????

quote:

Originally posted by Rick 0311:
The miniguns have multiple barrels but they fire from the same position as they rotate around the central axis, so in effect the bullets are all leaving the bore at the same indexed position(just like a Gattling Gun) as the previous barrel that fired and should therefore be “following†each other.

Obviously, since the aircraft is also moving there would be a dispersion, but what if the weapon was fired from a solid stationary platform????

Good point. Guess it depends on the mounting tolerances and damping of each barrel to actually determine whether the same exact track is followed. And who knows how much leeway there is there? Might be they don't have to follow the "exact" same track for any effect to become significant.

I wonder if there is any publicly available gov't info on such. I am virtually sure it must have come up in the Vulcan design engineering...

and to really complicate things how about the metal storm concept of mulitple projectiles from a single barrel? I think these are "fired" by electo magnetic impulses they are capable of incredible rates of fire and are used in Missle defense on ships? check out the link
http://www.metalstorm.com/

Somewhat related....

Was watching Fox News yesterday and they had a camera crew imbedded with an outfit from the 7th Marines in Ramadi,Iraq. They had a camera shot from just off to the side of a Mk 19 Grenade launcher and the guy popped off a three round burst. You could watch the grenades all the way to the target and they were pretty damned close to each other. It’s impossible to be exact but they were certainly not hundreds of feet apart, and the Mk19’s do not have a very fast cyclic rate.

According to Wikipediathe MK-19 is cycling 5 rounds per second!!! I could find no information regarding projectile velocity. My guestimate would be about 600 fps, maybe 800 max. Either of these rates of fire would allow for a minimum of 100 ft between projectiles.

I am sure they make an impresive turbulance trail, and even more "turbulance" when they hit their target!!

I am sure there are ballistics experts out there who know the answer....But they ain't talkin!!

The Mk19’s have a muzzle velocity of 780 fps...just over three times that of the 203’s and M79’s. They have a cyclic rate of 350 rpm.

I would bet that those big rounds lose velocity really fast.

My original question is probably meaningless with these types of weapons anyway since they are area weapons and not precision weapons where pin-point accuracy is required. I just was wondering how much effect, if any, the proceeding round has on the one following it, and if there is any cumulative effect from round to round.

Mass/shape of the projectile probably has influence on the amount of turbulence. Consider the sonic booms of a .17 caliber 25 grain bullet doing mach 4 and an F15 Eagle doing mach 2. You cannot hear either one comming; your ears will notice the .17 after passing you; your whole body will notice the F15 leaving the area. The F15 is displacing a lot more of this fluid-like stuff known as air. As I understand it, window panes have been known to part company with their frames.

RareBear,

Very good point. I live in the flight path for the Space Shuttle when it lands at Edwards Air Force Base and my entire house jolts when that sucker comes by.

I also know that jets can be adversely effected when getting into the turbulence of another aircraft...so I just wondered how, or if, this might effect rounds being fired from high cyclic rate full auto weapons. As I stated from the start, I don’t have any idea what the answer is but I thought the question was a valid one, and one I had not heard discussed before.

I asked this question of a currently serving member of the military and he told me that he witnessed some tests being done at Abberdine Proving Grounds on this very topic where they fired high cyclic rate weapons through smoke and filmed it with high speed cameras.

He told me that the built up turbulence that each successive bullet had to pass through was quite high.

Rick,
Are we shooting .45's out of an open door or .308's. MV has a big effect on how fast the bullet will go backwards when it leaves the barrel. As for turbulence and flight paths, the 20 MM in the CIWS fires a lot of rounds (900 RPS or so) and puts up a wall of rounds in front of the incoming missile not multiple rounds in one hole.

quote:

Originally posted by Sam:
Rick,
Are we shooting .45's out of an open door or .308's. MV has a big effect on how fast the bullet will go backwards when it leaves the barrel. As for turbulence and flight paths, the 20 MM in the CIWS fires a lot of rounds (900 RPS or so) and puts up a wall of rounds in front of the incoming missile not multiple rounds in one hole.

This isn’t a “practical†topic...just a “brain-teaser†to have fun with, which is why I used that term as the title of the thread.

I believe that it does have some validity though when designing any high cyclic rate weapon. As I’m sure you are aware, not all of these type weapons are used to put up “walls†of bullets to take out missles and incoming projectiles. Some of them (the guns on A10’s and Cobra’s) are used in CAS missions where accuracy is a major factor.

Let's not forget that though automatic weapons (LMG and above,) can be used on point targets, they are area fire weapons. In the class of weapons I've identified, even with a rock steady mounting, recoil, as well as barrel resonation, is such that it is about impossible to have a bullet follow another bullet's direct wake. MGs create a pattern of impacts known as the "beaten zone" that blankets a target area. Interestingly, Gattling guns were originally the property of the Artillery Branch and used as indirect fire. Anyway, that's what we learned at the Armor School.

quote:

Originally posted by Col K:
Let's not forget that though automatic weapons (LMG and above,) can be used on point targets, they are area fire weapons. In the class of weapons I've identified, even with a rock steady mounting, recoil, as well as barrel resonation, is such that it is about impossible to have a bullet follow another bullet's direct wake. MGs create a pattern of impacts known as the "beaten zone" that blankets a target area. Interestingly, Gattling guns were originally the property of the Artillery Branch and used as indirect fire. Anyway, that's what we learned at the Armor School.

I’ve already stated that this was a “brain-teaserâ€...not something that would have that much practical effect in the real world.

Obviously, if the Military did tests on it I am not the only person that has raised the question before.

I don’t pretend to know how much “wake†is left behind a bullet in flight...nor do I pretend to know how large or how long it stays there where it might have an effect on subsequent bullets passing through the same general proximity in the air.

Following this vein of thought: If you had an MG set up to fire through the screens of a chrono and recorded the MV of each successive round, what would a graph of the MV's look like? I would suspect there would be some slight increase in the MV of the following rounds but does anyone know for sure??????
Someone stated above about the dispersion of rounds from an MG on target - I seem to recall reading about this dispersal being discussed re fighter planes from WWII and reference made to the "Cone of Fire." Were they speaking to the POA being different for each of the multiple guns in the armament array or the different flight paths of projectiles from each MG?

I'd think that the turbulence behind a bullet fades out pretty quickly due to the small diameter of the bullet, but the disturbance of a previous muzzle blast would definitely be a significant factor for the next bullet coming out and that there would be some cumulative effect from sequential muzzle blasts' turbulence building up in front of a stationary machine gun.

quote:

Originally posted by Ricochet:
I'd think that the turbulence behind a bullet fades out pretty quickly due to the small diameter of the bullet, but the disturbance of a previous muzzle blast would definitely be a significant factor for the next bullet coming out and that there would be some cumulative effect from sequential muzzle blasts' turbulence building up in front of a stationary machine gun.

If you look at the high speed photos in Vaughn’s book it is amazing how large the wake behind the bullet, and the shock wave ahead of it, are. I’m not so sure that they would dissipate all that quickly with no wind.

I also agree with your observation about the muzzle blast.

Regarding - "Projectile Wake Turbulence Separation Critera"

Using the FAA standard.

Given:

30 Cal
Projectile Length(PL) 1"
3000 FPS
6000 Rounds Per Minute

At this speed and rate of fire the Estimated Projectile Interval(EPI), would be 30 Feet, or 360 Projectile Lengths (PL)

When compared to your average Boeing 747-400

Projectile Length - 2782"
Cruise speed - 565 StatuteMPH/829 FPS/

The FAA mandates that separation at cruise and 'in-trail', Projectile Interval(PL), between successive B747-400 shall be 5 Nautical Miles (NM) which is 30,000 feet.

This equates to a Projectile Interval(PI) of 129.4 Projectile Lengths(PL).

Since, the FAA is tasked with the Safe, Orderly and Expeditious flow of air traffic, and since, in the case of the B747-400, babies and Samsonite are at risk, and the aforementioned agency has determined that 129.4 PL does not place either babies or Samsonite at risk, I must conclude that bullets fired under the circustances above have little to no effect upon each other.


JAMSWTiCHO

That B747-400 cruises right at .45 Auto muzzle velocity.

Yeah, but the cross sectional area is a smidgeon larger, and they leave skids marks that would make an elephant blush.

I like Muffin's analysis, and God save the Samsonite! I also know you fellas are floggin' a stuffed horse for the most part. Best case scenario for intrail spacing comes from a Mini-gun at 6,000 RPM, and I don't think they use or make 'em like that anymore. You might also note the mini's are not common as ground based weapon systems, mostly because they eat ammo like Tony Montana goes thru nose candy, and it weighs a LOT. Anyhoo, unless I've been mislead the mini's are shooting at 3000 rpm these days, so double your interval before you whip out your calculator. Next issue is that since your platform is probably airborne, AND MOVING, it makes analysis of wake turbulence problematic at best, and more likely pointless. Even it your aircraft is straight and level, it is moving forward, thus each firing point is different...so is the arc of trajectory, even if aimed at the same point. Oh, one last point on this teaser.... if I were to spot you the point that wake turbulence or vortex, or whatever you wish to call it, if I granted it caused accuracy issues, then I am absolutely bumfuzzled how I could use a mini to burn holes in bunkers in Viet Nam, generally within 100 meters. I don't mean big holes...mostly less than 12" in diameter thru 3-5' of earth and logs. It would have also made engaging 12.7mm AA positions problematic out near 1000 meters....but it didn't, and I wasn't(bumfuzzled). You can call a mini-gun an area fire weapon, and rightfully so, but the area they beat ain't that big if you don't want it to be that way. An aside not relevant to the discussion...when you fired one of those from a position in sunlight, but the target is dark in color and under a cloud shadow, you can see ALL of the bullets, not just the tracers. The phenomona is called glimmer, and it is an awesome sight to behold. They aren't going all squiggley from wake turbulence either.

I think a better brain teaser is:

Which shoots better, an octagon barrel, round barrel, or a hexagon barrel with the peaks(corners of the flats) of the barrel at 12 and 6 o'clock. Assume all quality of manufacture issues are equal, point of discussion is barrel harmonics and heat effects, firing 20 rounds is a 10 minute time frame.

Note to class: NO BARREL BORE IS EVER PERFECTLY CONCENTRIC WITH ITS EXTERIOR PROFILE. You may assume a tapered profile or straight, and assume same minimum barrel wall thickness at a given datum for each type.

WHY?

quote:

Originally posted by mike_elmer:

quote:

Originally posted by Rick 0311:
I’ll add to the brain teaser.

What about a minigun firing at 6,000 rpm (100 rounds per second)?

Well, I would contend that it would require too much reloading and barrel cleaning!!!

I would also have to believe, if the gun is held steady enough so the bullets are following in the previous bullets path, that the turbulence would have to affect the grouping of a string of shots.

Which is a really big "if".

If I'm not mistaken the "Mini gun" is regulated to only about 2000rpm or so and is ultimatly limited by the ability of the mechanical firing pins to cycle.

The M61 "Vulcan" (for Alberta Canuck's benefit) 20mm Aircraft cannon does fire at 6000rpm, but they use electrically primed ammo and are not mechanically limited.

And in either case the barrels are intentionally set so that the bullets do not follow the same path to generate that "cone" of fire rather than a harder to hit with "stream"
of fire.

The 30mm "Avenger" cannon in the A10 tank buster
has seven barrels and the weapon occupies nearly the entire length of the fuselage
the A10 was literally designed around the gun.



The Seaborne version of the vulcan 20mm cannon is called CIWS (Close In Weapon System) and the radar actually tracks individual projectiles outbound.

I've been told that the CIWS has the barrels
tuned so that unlike the aircraft cannon
the "bullets" follow a tight stream
On their way outbound... this makes it easier to adjust aim at a 12" diameter missile as the computer adjusts the bullet stream so it and the missile merge, if the barrels were set to
"scatter" the rounds this would be far more difficult.

And adoption of CIWS caused a change in 20mm projectile design, the heel of the 20mm projectiles were changed to provide a better radar return for the CIWS radar and computer, bacsically a concave recess was made in the back of the projectile in a "reverse stealth"
move to focus the radar return back at the ship that fired the projectile....

and unlike a fighter jet that only carries 500-550 rounds (the F15 Eagle carries 750rounds) a ship isn't likely to run out of ammo and can carry multiple sets of spare barrels.

there was to be an Anti Ballistic Missile defense version of the 30mm Avenger cannon as a "point defense" at ICBM bases but they never built or deployed them.

AllanD

The Vulcan’s and the Mini guns (same basic design) only fire the rotating barrels at one position...TDC.

Since these are normally only found on airborne platforms its somewhat academic since the platform is normally moving at a pretty good clip when they are fired.