Dispersion Angle for rapid fire WW2 aircraft guns

[straffo]

Thank you

At least I didn't put an accent in sustainèd fire ... oops I just did

[gripen]

Originally posted by Crumpp

I guarantee you Gripen those pins are there for the exact same reason, ease of deployment or removal.  Although they add dispersion that is a flaw not a feature.

If you disassemble the gun, you can even measure couple mm loosenes from the rectangular mounting supports. It wont make any easier or difficult to assemble the gun if these were tighter.

Besides, our instructors as well as documentation told that it's there for dispersion.

gripen

[Crumpp]

You could get different barrel clamps for the M61A1, which gave different dispersion patterns (including a wide one) by varying the spacing between the barrels. Don't know if that saw any use, though.

Hi Tony,

Looks like those may have been an attempt to reduce the dispersion which is usually the case in gun design.

Check out this Raytheon advertisement for the Phalanx system under "optimized barrels":

http://www.raytheon.com/products/stellent/groups/public/documents/content/cms01_055720.pdf

"Original M61A1 gun barrels were designed for short bursts and subject to wear and increased dispersion patterns."

All the best,

Crumpp

[Tony Williams]

I have an original GE '20mm Weapons Applications Data' handbook, with lots of technical stuff about the M61 family. It includes information about three different muzzle clamps which were available, together with nice shot pattern diagrams to show the effects of them. They are (for 100% of shots):

1 - Standard: circular pattern, 4.5 mils.

2 - Oval: 8 mils high by 38 mils wide.

3 - Large Dispersion: circular pattern, 16 mils.

The text states that: "The M61A1 gun normally produces a small circular dispersion pattern at the target. However, certain missions or targets may call for greater than normal dispersion. Still other targets may call for an oval pattern for increased hit probability. Such increased dispersion or pattern distortion can be obtained by substitution of a special muzzle clamp."

As I said, I have no idea whether any of these special muzzle clamps were ever used, but GE obviously thought that there might be a demand for them.

Tony Williams: Military gun and ammunition website and discussion forum

[Tony Williams]

Originally posted by Crumpp
The M2 is considered a very flat trajectory MG and very accurate.  It has a 4 mil dispersion cone.

The first point is to clarify whether we are talking about the figure for 100% or the often-quoted 75% of shots (the latter being typically half the size of the former). Then there is the question of the mounting.

Yes, the .50 M2 could achieve 4 mils for 75% of shots, from a rigid mounting. But that is not very accurate, in fact it is among the worst of WW2 aircraft guns.

That is not too surprising, as the Browning uses a short-recoil action which means that the barrel is not fixed but has to be free to move to and fro. That also helps to explain why the short-recoil MG 151 had far more dispersion than the fixed-barrel MG-FF (another part of the reason was that long barrels tend to 'whip' more than short ones, so have more dispersion).

And all that leaves entirely aside the issues already mentioned of the flexibility of the mountings (wings being worse than fuselages) or convergence effects for wing-mounted guns, or 'aim wander', all of which had a considerable effect on the overall shot pattern.

Tony Williams: Military gun and ammunition website and discussion forum

[HoHun]

Hi Tony,

>Yes, the .50 M2 could achieve 4 mils for 75% of shots, from a rigid mounting. But that is not very accurate, in fact it is among the worst of WW2 aircraft guns.

Are you certain that 4 mils is the 75% dispersion circle diamter and not the 100% one? I beleive that in the old thread referenced above, Butch2k quoted 4 mil for the Browning and 3 mil for the Hispano as 100% dispersion circles.

Regards,

Henning (HoHun)

[butch2k]

Nope that was for the 75% dispersion

[Crumpp]

As I said, I have no idea whether any of these special muzzle clamps were ever used, but GE obviously thought that there might be a demand for them.

Hi Tony,

Interesting.  Guess there was not a demand for them if added dispersion was not needed to bring down a small fast moving target like a missle.

But that is not very accurate, in fact it is among the worst of WW2 aircraft guns.

Interesting.  Well that is a myth down the tubes then.


All the best,

Crumpp

[HoHun]

Hi Butch,

>Nope that was for the 75% dispersion

Thanks for the correction! That does of course have a serious impact on my example!

I'll double all dispersion figures (including the German ones, after re-reading your post in the old thread) and re-run my example:

The MK108 will still hit accurately out to 500 m, but be virtually useless beyond.

The wing-mounted Brownings set to 250 m convergence will be a ineffective at 100 m if the pilot aims at the target fuselage because of convergence. (Easy to fix by kicking rudder, of course.) At 200 m, maybe 40% of the fire will be on target, at 250 m it's 80%, and at 300 m it's only 30%. (Note the way the hit ratio peaks at convergence range!) At 400 m, the horizontal stabilizer will be showered and there might be a few random hits on the fuselage. At 500 m and beyond, hit chances are very small.

With the nose-mounted Brownings, out to 200 m, the fire will hit virtually without a miss. At 300 m, the hit ratio will drop to maybe 80%, at 700 m it will only be about 20%. At 800 m, trajectory drop will roughly halve the hit chances, and at 1000 m they will be maybe 5% or less.

So the three example batteries still show the problems I orginally described, but the conclusions are a bit different.

For the Me 109, not much has changed because its dispersion is rather small.

The P-47 is limited in its range primarily by the divergence of its fire, and dispersion means that its fire loses effectiveness rapidly at long range. Firing at beyond 500 m probably won't be worth it, though it's still possible to envelop the target in tracers for tactical effect and score a handful of hits with a long burst.

The P-38's battery still is the best for long-range shooting, and a thee-second burst at that range might yield a fair chance of bringing an enemy fighter down. (The probability will, say, double if the Hispano cannon I neglected in my above consideration is added to the battery.)

So the P-38 is a real long-range killer if there ever was one! I stick to that comment ;-)

Regards,

Henning (HoHun)

[HoHun]

Hi Tony,

>I have an original GE '20mm Weapons Applications Data' handbook, with lots of technical stuff about the M61 family. It includes information about three different muzzle clamps which were available, together with nice shot pattern diagrams to show the effects of them. They are (for 100% of shots):

>1 - Standard: circular pattern, 4.5 mils.

>2 - Oval: 8 mils high by 38 mils wide.

>3 - Large Dispersion: circular pattern, 16 mils.

Thanks, that's interesting information! An A-10 pilot who usually provided very reliable information once told me about a similar purposefully increased dispersion for the 30 mm Gatling on the A-10. Of course, that was meant for attacking ground targets, and at least the wide oval pattern you quoted suggests that it was meant for ground attacks, too. A circular pattern does not suggest any particular target, but considering that the M61 is not a one shot MiG killer by any means, I'd suspect that the large dispersion setting was not really intended for air combat either. That's just my personal guess, of course :-)

Regards,

Henning (HoHun)

[Tony Williams]

Originally posted by HoHun
An A-10 pilot who usually provided very reliable information once told me about a similar purposefully increased dispersion for the 30 mm Gatling on the A-10. Of course, that was meant for attacking ground targets, and at least the wide oval pattern you quoted suggests that it was meant for ground attacks, too.

From Flying Guns – the Modern Era: Development of Aircraft Guns, Ammunition and Installations since 1945:

The 30 mm GAU 8/A in the A 10 "tankbuster" can get 80% of its shots within 5 mil, equal to 9 m dispersion at the 1,800 m maximum range. On test, the A-10 managed to hit a tank with about 10% of the shots fired at ranges varying between 500 and 1,340 m; a performance which has almost certainly improved since the LASTE package (low altitude safety and target enhancement), including a radio altimeter, autopilot and ballistic computer, was fitted in the 1990s. Incidentally, of the hits scored (against Russian T-62 tanks) just under 20% penetrated the armour (i.e. 2% of shots fired), although many others extensively damaged the track and suspension.

Tony Williams: Military gun and ammunition website and discussion forum

[gripen]

Originally posted by HoHun
A circular pattern does not suggest any particular target, but considering that the M61 is not a one shot MiG killer by any means, I'd suspect that the large dispersion setting was not really intended for air combat either. That's just my personal guess, of course :-)

That certainly depends on your personal abilities; if you can aim more accurately at long range to the moving targets than stationary targets, then your personal quess is correct.

gripen

[HoHun]

Hi Tony,

>Incidentally, of the hits scored (against Russian T-62 tanks) just under 20% penetrated the armour (i.e. 2% of shots fired), although many others extensively damaged the track and suspension.

Highly interesting! I'd say in conjunction with the info from the loss analysis linked by Crumpp (pointing out that 50% of the A-10 losses were due to SA-16 MANPADS), that suggests that gun-armed slow-movers are not a good choice for today's battlefield environment.

Regards,

Henning (HoHun)

[HoHun]

Hi again,

Some additional numbers on my example:

The Me 109's MK108 will hit with about 8 - 10 shells per second out to 500. That's equal to about 4 - 5 MW of total firepower on target. At 550 m, firepower on target will be down to 4 hits/s or 2 MW, at 600 m there will be no hits :-)

The P-47's wing mounted Browning are more complicated:

100 m*: 26 hits/s -> 0.57 MW
200 m: 42 hits/s -> 0.91 MW
250 m: 83 hits/s -> 1.82 MW
300 m: 31 hits/s -> 0.68 MW
400 m: 10 hits/s -> 0.23 MW

* aim laterally offset to hit fuselage

The nose-mounted Brownings yield the following results:

100 m: 52 hits/s -> 1.13 MW
200 m: 52 hits/s -> 1.13 MW
300 m: 42 hits/s -> 0.91 MW
700 m: 10 hits/s -> 0.23 MW
800 m: 05 hits/s -> 0.11 MW
1000 m: 2.6 hits/s -> 0.06 MW

Regards,

Henning (HoHun)

[gripen]

I have compared the new AH K-4 to the AH P-47D-11. At long range between 600-800, I can definately kill the drone B-24 easier with with the P-47 than with the K-4. It's just much easier to get correct lead with the 8 mgs and the needed lead seem to be less ie there is less room for error. Generally it seems that in long range deflection shooting, the amount of bullets (more hits) and velocity of the bullets (less lead needed) are the most important factors.

gripen

edit: Convergence was default.