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XyZspineZyX
09-08-2003, 03:16 PM
For those so interested, the following comes from AF Manual 335-25 FIGHTER GUNNERY, dated Dec 1950 -

QUOTE -

With an F-80 harmonized at 350mph IAS for a 1,000 foot range, the trajectory of the bullet will cross the sight line the first time at 1,000 feet. The trajectory will rise gradually to a height of 7 inches above the sight line and then will fall, recrossing the sight line again at 2,000 feet. (snip) With a cone of dispersion (the cone of bullet dispersion from a caliber .50 machine gun is about 4 mils for 75 percent of the rounds and 8 mils for 100 percent of the rounds) of 8 mils, or 16 feet at 2,000 feet, 6 guns (M2) firing 72 rounds per second give a bullet density of one bullet per 2.8 square feet per second, ...

- UNQUOTE

To put this in better perspective, the bullet density within the "75 percent zone" for 6 x M2 .50cal MG's at a convergence of 333 yards (about 300 meters) range will be about 1.1 rounds per square foot per second.

... and the bullet density for the "50 percent zone", which can will be roughly about 2 mils is about 2.8 bullets per square foot per second under the above-mentioned conditions. A 2 second burst would put 3 .50cal rounds into every square foot of an approximately circular target disk just shy of 13 square feet in area (4 foot diameter). For our European colleagues, this equates to 36 strikes per second within an area slightly larger than 1 square meter.

If convergence was set at 600 feet (200 yards) the effect on target would be about 1.67 times greater.

A P-47 with 8 x .50's would show 1.33 times better performance.

Also notice that, between 1,000 feet and 2,000 feet, the vertical separation between bullet path and line of sight does not exceed 7 inches. This remains ballistically true for some distance less than 1,000 feet and greater than 2,000 feet as well.

In terms of horizontal separation, assuming that wing guns are separated by an average of 15 feet on the airplane and are adjusted to converge at 1,000 feet, the bullet streams will be about 7.5 feet apart at 500 feet (167 yards) and 3.25 feet (1 meter) at 750 feet (250 yards).

Please note that all above discussions relate to the WW2 period M2 model of the .50cal. Pretty effective against a fighter target, I would say.



Blutarski

XyZspineZyX
09-08-2003, 03:16 PM
For those so interested, the following comes from AF Manual 335-25 FIGHTER GUNNERY, dated Dec 1950 -

QUOTE -

With an F-80 harmonized at 350mph IAS for a 1,000 foot range, the trajectory of the bullet will cross the sight line the first time at 1,000 feet. The trajectory will rise gradually to a height of 7 inches above the sight line and then will fall, recrossing the sight line again at 2,000 feet. (snip) With a cone of dispersion (the cone of bullet dispersion from a caliber .50 machine gun is about 4 mils for 75 percent of the rounds and 8 mils for 100 percent of the rounds) of 8 mils, or 16 feet at 2,000 feet, 6 guns (M2) firing 72 rounds per second give a bullet density of one bullet per 2.8 square feet per second, ...

- UNQUOTE

To put this in better perspective, the bullet density within the "75 percent zone" for 6 x M2 .50cal MG's at a convergence of 333 yards (about 300 meters) range will be about 1.1 rounds per square foot per second.

... and the bullet density for the "50 percent zone", which can will be roughly about 2 mils is about 2.8 bullets per square foot per second under the above-mentioned conditions. A 2 second burst would put 3 .50cal rounds into every square foot of an approximately circular target disk just shy of 13 square feet in area (4 foot diameter). For our European colleagues, this equates to 36 strikes per second within an area slightly larger than 1 square meter.

If convergence was set at 600 feet (200 yards) the effect on target would be about 1.67 times greater.

A P-47 with 8 x .50's would show 1.33 times better performance.

Also notice that, between 1,000 feet and 2,000 feet, the vertical separation between bullet path and line of sight does not exceed 7 inches. This remains ballistically true for some distance less than 1,000 feet and greater than 2,000 feet as well.

In terms of horizontal separation, assuming that wing guns are separated by an average of 15 feet on the airplane and are adjusted to converge at 1,000 feet, the bullet streams will be about 7.5 feet apart at 500 feet (167 yards) and 3.25 feet (1 meter) at 750 feet (250 yards).

Please note that all above discussions relate to the WW2 period M2 model of the .50cal. Pretty effective against a fighter target, I would say.



Blutarski

XyZspineZyX
09-08-2003, 05:20 PM
BLUTARSKI wrote:
- For those so interested, the following comes from AF
- Manual 335-25 FIGHTER GUNNERY, dated Dec 1950 -
-
- QUOTE -
-
- With an F-80 harmonized ...

just a few pedantic points..

The results for a P47 would be somewhat different.
The P/F-80 has all the guns mounted in the nose,
reducing the following:

The effect of convergence relative to gun mountings

Much less dispersion due to vibration

Much less effect of relative roll of aircraft.

In other words, you'd expect the bullet density of an
P/F-80 to be higher than a plane with 6 wing mounted
.50s. As to the comparasion with an 8 gun fighter,
that's another matter.

XyZspineZyX
09-08-2003, 07:10 PM
AaronGT wrote-
- The results for a P47 would be somewhat different.
- The P/F-80 has all the guns mounted in the nose,
- reducing the following:
-
- The effect of convergence relative to gun mountings
-
- Much less dispersion due to vibration
-
- Much less effect of relative roll of aircraft.


The afore-mentioned gunnery manual, which addresses the F47 and F51 as well as more modern jet a/c, is altogther silent on the matter of wing vibration affecting gun accuracy. Does anyone have any data citations on the effects of wing vibration, or is this perhaps a logical assumption which is not actually supported by the facts?

The manual does mention bank and roll effects when shooting beyond 400 yards.



Blutarski

XyZspineZyX
09-08-2003, 07:33 PM
read this, It was my post a long time ago:

I do agree that the 50 cal. was not as powerful as it should be pre-patch, but all of you 50 cal. whiners complaining must not really know what it is capable and incapable of! There are a number of concepts which you don't understand, except basic ballistics, where the bigger and faster a round is, the more destructive it is, etc...

Lesson 1: Bullets vs. Cannons

All cannon rounds were bullets but not all bullets were cannon rounds. Yes, it's one of those jobbies. A cannon is really just an explosive bullet with a few complications here and there. Some are more powerful than others, yes, but the 50 cal. is not a cannon. It's a bullet. Meaning one bullet won't do a lot of damage. It punctures a hole, it doesn't explode unless it sparks something flammable. You need a whole lot of the bullets to cause a whole lot of damage. Which brings us to...

Lesson 2: Bullet Spread and Convergence:

Bullet spread is related to convergence. Convergence is setting the guns up so that the bullets connect or cross paths at a certain point. This is also known as concentrated fire. bullet spread is basically how far apart the bullets are. The P-47, from the left-most round to the right-most round is a considerable distance, so the bullets are spread out right from the start. The more guns, the bigger the bullet spread. This goes only for guns mounted in the wings. Guns mounted in the nose have convergence for up and down, not left and right. Since nose guns are already centered, almost no convergence is needed.
Example 1:

plane convergence set to: 20 meters- plane fires at twenty meters at an engine- RESULT: the engine should be thouroughly destroyed or the armor around it should be punctured well.

let's say the plane fired at fifty meters, then the bullets spread out too far and only hit a few times in many different places on the plane, not that effective.

if the plane is firing at 10 meters, then the pilot isn't giving the bullets enough range to converge, so the guns will hit two separate points on the target, say on both wings, but the bullets can't do as much damage because the ammunition wasn't concentrated at one point.

I'm sure you know about deflection shots and the fact that the farther a bullet goes it loses speed and power, so try to set the convergence to small distances. At most 200 meters, at least, 10 meters. In the game: .18 on an icon means 180 meters. When they say height 30 in a mission, it means 300, if they say 300, it means 3000. if they say 3000, you know they're talking feet because you can't get to 30,000 meters easily. I hope this helps with you 50 cal. problems.

Boosher-PBNA
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XyZspineZyX
09-08-2003, 07:38 PM
Gentlemen,
Here is an excellent page on Gunnery in WarBirds:
"Ogre's Gunnery Effects Study"
http://www.concentric.net/~reaper/gunnery/gunnery.html
Granted - it is about WB but it is most educational and very relevant to the meter you are discussing here.

All is interesting, but especially this page on dispersion:
http://www.concentric.net/~reaper/gunnery/fvsvfw.html

And this one on hit probability at convergence:
http://www.concentric.net/~reaper/gunnery/hvz_at.html



AKA_Bogun

---------------
The difference between fiction and reality? Fiction has to make sense.

- Tom Clancy


Message Edited on 09/08/0302:39PM by Bogun

XyZspineZyX
09-08-2003, 08:47 PM
Bogun,

Agree, an interesting site which I have visited in the past. The author's analyses, although related to a flight sim, are generally in accord with the .50cal dispersion data given in the FIGHT GUNNERY manual from which I quoted. His strike diagrams are also valid if the assumption is made that the Hellcat's guns are point converged (or harmonized) at each of the specified diagram ranges.



Blutarski

XyZspineZyX
09-08-2003, 09:25 PM
It was "eye opening experience" for me to realize how much normal bullet dispersion affect the hit probability even if shooting is taking place under <u>best</u> circumstances - i.e. at convergence distance, no deflection. %36 at 300 yards. Imagine shooting while trying to maneuver with any kind of G-load where a normal wing flexing is going to become a factor? Or in dive.


Here is a diagramme of P-47 with its eight harmonized at two convergence points (250 and 350 yards):
http://www.zenoswarbirdvideos.com/Images/P-47/47GECD.gif


AKA_Bogun

---------------
The difference between fiction and reality? Fiction has to make sense.

- Tom Clancy


Message Edited on 09/08/0304:29PM by Bogun

XyZspineZyX
09-08-2003, 09:36 PM
Boosher-PBNA wrote:
- read this, It was my post a long time ago:


..... I did read your earlier post on this topic. And please note that I am not indulging in any whining about .50cal effectiveness. I'm just posting some interesting info which I turned up over the weekend in my library.



- Lesson 1: Bullets vs. Cannons
-
- All cannon rounds were bullets but not all bullets
- were cannon rounds. Yes, it's one of those jobbies.
- A cannon is really just an explosive bullet with a
- few complications here and there. Some are more
- powerful than others, yes, but the 50 cal. is not a
- cannon. It's a bullet. Meaning one bullet won't do a
- lot of damage. It punctures a hole, it doesn't
- explode unless it sparks something flammable. You
- need a whole lot of the bullets to cause a whole lot
- of damage. Which brings us to...

..... I don't disagree. An individual explosive round will generally do more damage to an airframe target than an individual kinetic energy round. And it is pretty clear that the best all round air-to-air weapon of WW2 was a high velocity 20mm cannon. But the comparison between weapons firing kinetic energy rounds and those firing explosive rounds can be complicated by various factors such as rate of fire, muzzle velocity, ballistic efficiency of the projectiles, time of flight, fusing method of explosive rounds, and the nature of the a/c component struck. For example: it is quite possible that a .50cal AP round maydo a better job against armor plate than will a 20mm HE round.



- Bullet Spread and Convergence:
-
- Bullet spread is related to convergence. Convergence
- is setting the guns up so that the bullets connect
- or cross paths at a certain point. This is also
- known as concentrated fire. bullet spread is
- basically how far apart the bullets are. The P-47,
- from the left-most round to the right-most round is
- a considerable distance, so the bullets are spread
- out right from the start. The more guns, the bigger
- the bullet spread. This goes only for guns mounted
- in the wings. Guns mounted in the nose have
- convergence for up and down, not left and right.
- Since nose guns are already centered, almost no
- convergence is needed.

..... "Bullet spread" originates from two principal sources: the natural dispersion of each weapon; and the manner in which these weapons are converged or harmonized. Point convergence at a given range is only one method of gun harmonization. An examination of USAF gun harmonization diagrams very commonly show the practice of "pattern harmonization", in which the guns were separately aligned to produce a pattern of overlapping individual dispersion patterns. This was done even with a/c featuring all nose-mounted armament. The result was the creation of a large volume of space swept by a reasonably deadly density of fire, as opposed to the intensely lethal density over a much smaller area created by point convergence.

Also, recall that ballistic dispersion is not evenly distributed within the hitting zone. At any given range: 50 pct of bullet strikes will occur within a radius of 1 mean error from the mean point of impact; 82 pct of strikes will occur within a radius of 2 mean errors; 96 pct within a radius of 3 mean errors; and 100 pct within a radius of 4 mean errors.



Blutarski

XyZspineZyX
09-08-2003, 10:15 PM
Bogun,

I'd imagine that the 250 yd harmonization was for fixed reticle gunsights and the 400 yd harmonizatin was for the K14 gyro gunsight.

The diagrams can be a little misleading, since the distancee scale are not constant. Lay out the bullet dispersion patterns for the guns and see how the hitting patterns emerge at various ranges around the convergence point. Even at 400 yds range with a 250 yd point convergence, about 80 pct of rounds will still strike within a horizontal oval of about 200 square feet (approx 10 x 22 feet). An 8 gun burst of the recommended two seconds duration from a P47 would then still give a striking density of about one round per square feet. It's very interesting and shows that some considerable thought went into these methods.

The big problem was pilot aiming. Here is what the manual states about pilot aim with a fixed reticle (circa WW2) gun sight -

QUOTE -
At a 1,000 foot range, it is difficult for even an expert to hold his sight within 5 or 6 feet of the desired aiming point, and at 1,500 feet it is difficult to hold the sight within 8 or 9 feet. Therefore, since fighter aircraft represent a relatively small target area, the pilot's ability to aim becomes a major limitation of effective range.
- UNQUOTE



Blutarski

XyZspineZyX
09-08-2003, 10:34 PM
200 to 300m sounds about right. My unit flew a coop today w/ Jugs and there were 190's as oppostion. One of our guys caught up to one of them and started a 2 second burst at 300m by the time he made 200m the 190 exploded. I have fire at them in the past w/ a 400m setting and just shot it up but did not bring it down.

Btw 300yds = 274.4m if is any help

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Message Edited on 09/08/0308:36PM by Sniper762x57