Hit rate- cannons vs mg

[HoHun]

Hi Suntracker,

>I believe due to wing resonance, that bullets were lucky to hit in a 12ftx12ft box at 300 yards.  

Sure. But the Browning M2 had about the largest dispersion among all WW2 guns for which I've seen data, and cannon like the Hispano II and the MG151/20 were more accurate.

>So 30-50 seconds of firing time, compared to as little as 8 seconds for some cannon armed planes, was a big benefit.  

This is a list of batteries selected to give approximately 2.3 MW firepower (equivalent to 8 x Browning M2) at 30 s firing duration:

1x MK 108 - 300 rpg - 236 kg - 5 MW firepower - firepower per weight: 21,4 kW/kg
1x MK 103 - 210 rpg - 334 kg - 4,1 MW firepower - firepower per weight: 12,2 kW/kg
2x MG 151/20 (MX) - 360 rpg - 238 kg - 2,8 MW firepower - firepower per weight: 11,8 kW/kg
2x MG 151/20 - 360 rpg - 238 kg - 2,5 MW firepower - firepower per weight: 10,7 kW/kg
2x Hispano V - 360 rpg - 261 kg - 2,5 MW firepower - firepower per weight: 9,5 kW/kg
2x Hispano II - 300 rpg - 248 kg - 2,1 MW firepower - firepower per weight: 8,6 kW/kg
3x MG-FF - 240 rpg - 328 kg - 2,3 MW firepower - firepower per weight: 7,1 kW/kg
5x MG 151 - 360 rpg - 538 kg - 2,2 MW firepower - firepower per weight: 4,1 kW/kg
11x MG 131 - 450 rpg - 573 kg - 2,3 MW firepower - firepower per weight: 4 kW/kg
8x ,50 Browning M2 - 390 rpg - 575 kg - 2,3 MW firepower - firepower per weight: 3,9 kW/kg
26x Browning ,303 - 600 rpg - 728 kg - 2,3 MW firepower - firepower per weight: 3,1 kW/kg

As you can see, the Browning battery weighs 575 kg, compared to the MG151/20 battery with just 238 kg.

In other words, your aircraft becomes 743 lbs lighter just by stepping up to 20 mm cannon! =8-O

If you want 50 s firing duration, the cannom advantage increases to more than 1000 lbs.

Regards,

Henning (HoHun)

[SunTracker]

But that brings me back to my original point.  A pilot firing cannons would not have the same amount of shells in the air, nor the dispersion if firing with 1 or 2 cannons.

So basically it all comes down to this.  At the average engagement distance, would it be easier to land 20-30 hits with 6 50 cals (the average U.S. Armament), or would it be easier to land 2-5 cannon hits with two cannons (the standard cannon armament)?

6X800rpm=4800rpm.  4800rpm/60=80 rounds per second.  It would take a 1/4th second burst to down an enemy aircraft.  Though indiviudal machine guns could be ramped up to 950 rounds per minute by armorers.

Hispano MkII= 600rpm.  600rpmx2=1200rpm/60=20 rounds per second.  Figuring 2 rounds to down an enemy aircraft, it would take 1/10th of a second.  Figuring 5 rounds, it would take 1/4th of a second.

[HoHun]

Hi again,

Here are the same batteries, but this time with so much ammunition to bring them all up to the weight of the 8 x Browning M2, 30 s firing duration battery:

1x MK 108 - 881 rpg, 88 s duration - 575 kg - 5 MW firepower - firepower per weight: 8,7 kW/kg
1x MK 103 - 472 rpg, 67 s duration - 575 kg - 4,1 MW firepower - firepower per weight: 7,1 kW/kg
2x MG 151/20 (MX) - 1149 rpg, 96 s duration - 575 kg - 2,8 MW firepower - firepower per weight: 4,9 kW/kg
2x MG 151/20 - 1149 rpg, 96 s duration - 575 kg - 2,5 MW firepower - firepower per weight: 4,4 kW/kg
2x Hispano V - 998 rpg, 83 s duration - 575 kg - 2,5 MW firepower - firepower per weight: 4,3 kW/kg
2x Hispano II - 966 rpg, 97 s duration - 575 kg - 2,1 MW firepower - firepower per weight: 3,7 kW/kg
3x MG-FF - 484 rpg, 61 s duration - 575 kg - 2,3 MW firepower - firepower per weight: 4,1 kW/kg
5x MG 151 - 401 rpg, 33 s duration - 575 kg - 2,2 MW firepower - firepower per weight: 3,8 kW/kg
11x MG 131 - 452 rpg, 30 s duration - 575 kg - 2,3 MW firepower - firepower per weight: 4 kW/kg
8x ,50 Browning M2 - 390 rpg, 30 s duration - 575 kg - 2,3 MW firepower - firepower per weight: 3,9 kW/kg
26x Browning ,303 - 404 rpg, 20 s duration - 575 kg - 2,3 MW firepower - firepower per weight: 4 kW/kg

Again, the 0.50" Browning M2 battery compares quite poorly, the Hispano and MG151/20 batteries getting about three times the firing duration from the same total weight at the same firepower.

Regards,

Henning (HoHun)

[63tb]

If the 20mm was superior (especially the Hispano) to the .50, why didn't the British and Americans use them for bomber defense? I see that they might be tough for hand-held positions but they would work in a turret mount, right? Wouldn't  a 20mm be a better defensive weapon too?

63tb

[HoHun]

Hi Suntracker,

>But that brings me back to my original point.  A pilot firing cannons would not have the same amount of shells in the air, nor the dispersion if firing with 1 or 2 cannons.

Number of rounds or dispersion don't increase your probability of a kill.

A higher number of less destructive projectiles with larger dispersion just ensures that you get a lot of subcritically damaged targets.

That was the actual German combat experience, and the reason they went to projectiles capable of destroying the aircraft structure immediately.

>So basically it all comes down to this.  At the average engagement distance, would it be easier to land 20-30 hits with 6 50 cals (the average U.S. Armament), or would it be easier to land 2-5 cannon hits with two cannons (the standard cannon armament)?

The most important factor is firepower. Here's a comparison of real batteries:

Me 262:       20,1 MW
Fw 190A-8/R2: 13 MW
Fw 190A-8:     5,5 MW
Me 109K-4:     5,5 MW
Tempest:       4,9 MW
Fw 190A-4:     4,3 MW
Typhoon:       4,2 MW
Spitfire IXE:  2,7 MW
Spitfire VC:   2,5 MW
P-47D:         2,3 MW
P-38:          2,2 MW
Me 109G-6:     1,8 MW
Me 109E-4:     1,7 MW
P-51D:         1,7 MW
Me 109G-2:     1,6 MW
P-51C:         1,1 MW
Hurricane IIA: 1,1 MW
Spitfire II:   0,7 MW
Me 109F-2:     0,6 MW
Me 109E-1:     0,3 MW

Regards,

Henning (HoHun)

[HoHun]

Hi 63tb,

>If the 20mm was superior (especially the Hispano) to the .50, why didn't the British and Americans use them for bomber defense? I see that they might be tough for hand-held positions but they would work in a turret mount, right? Wouldn't  a 20mm be a better defensive weapon too?

It would! Note that even the USAAF, otherwise dedicated to the Browning M2, added a 20 mm cannon to the B-29 tail, recognizing its superior power.

(It got pulled out when Le May did away with most of the defensive armament of his B-29s and went for night raids, and Korean War B-29s had a 12.7 mm MG in its place. They were facing jets with 23 mm and 37 mm cannon then ...)

Fitting 20 mm cannon in turrets can be difficult, though, and even the countries that did use them confined them to the positions most likely to see action (or the front position, which would have only very limited firing time in a head-on pass).

Regards,

Henning (HoHun)

[SunTracker]

HoHun, I don't believe your table takes into account the different factors of aerial gunnery.  Muzzle velocity, shell trajectory, recoil vibrations.

According to your table, wouldnt a B-25H reign supreme, with its 75mm cannon?

[Kweassa]

Suntracker, you have to take note that 'more shells in the air with faster firing time' is still only about effective as a single cannon fire. As Karnak points the US Navy has determined a single 20mm Hispano cannon is worth three M2 50cals.

 In reverse logic, it means to achieve the overall effectiveness a single 20mm cannon would wield, you needed more guns, more shells, and more hits to the same spot on the surface, plus the negative effect of the sheer weight of the weaponery as oppsed to a single 20mm cannon.

 Why attach three M2 50cals which needed more space and added more weight, when a single 20mm cannon could do the same thing?

 Theoretically a gun with a flatter trajectory and faster rate of fire would greatly benefit in the ability to hit at far distances.

 However, this is only taking ballistics and figures into the equation. There are more factors to aerial gunnery than just ballistics and RPM and velocities, and these very factors prevented practically ALL form of weaponery to be more or less useless when over 400m distances.

 According to Mr.Williams the absolute limit of successful gunfire against fighters would be around 200m, for bombers around 400m. Anything further out than that, and it made no difference whether or not a plane was armed with 20mms or 50cals - the distance was simply too far, and you couldn't hit it.

 Better trajectory and rate of fire brings proportionate increase in hitting chances only upto a certain distance. Further out than that, other factors intervene and drop the effectiveness drastically for all guns.

 Thus, the only real effective firing range would be inside 200m, where there wasn't any large difference between the 20mm cannons and .50 guns.


 
 Imagine you're in a P-51. You see a Fw190 in front of you and fire 6x 50 cals.

 You'd achieve more hits than 20mms, yes. But all of those hits still mount up to the amount of practical damage mere two 20mm cannons would do.

 To make matters worse, the sheer number of armament would mean the guns needed to be placed at the wings, and were very sensitive to harmonization. Dispersion and spread would scatter the limited number of hits even more on the Fw190.

 And if you were in a typical BnZ pass, you're window of chance would be small due to the quick approach speeds.

 Now, imagine if it was a Spitfire, landing only two cannon hits whereas a P-51D would land 10~15 hits all over the Fw190. Only two hits it is, but it would blow whole chunks off the enemy plane, immediately effecting its flight capabilities.

 With the .50s, you have to hope one of the 10~15 hits achieved snagged a delicate internal system. With the 20mms, it doesn't matter - you land even one hit, and the enemy plane will be forced to fly with a hole the size of your computer monitor on its surface.

[Tony Williams]

Originally posted by 63tb
If the 20mm was superior (especially the Hispano) to the .50, why didn't the British and Americans use them for bomber defense? I see that they might be tough for hand-held positions but they would work in a turret mount, right? Wouldn't  a 20mm be a better defensive weapon too?

63tb

Yes. The problem was that 20mm guns required a much bigger turret design, able to take the recoil. And it was not a simple task to fit a bigger turret to an existing plane - the bombers were usually designed around a certain size of turret.

In contrast, it was a relatively simple task to strap a bigger gun onto a fighter, so fighters were always able to keep ahead in the firepower race.

Furthermore, better turrets were a relatively low priority for the RAF because they bombed mainly at night, but even so they were working on some 20mm-armed bombers right at the end of the war.

Tony Williams: Military gun and ammunition website and Discussion forum

[HoHun]

Hi Suntracker,

>HoHun, I don't believe your table takes into account the different factors of aerial gunnery.  Muzzle velocity, shell trajectory, recoil vibrations.

Well, the latest table lists bare firepower and includes muzzle velocity for the calculation of energy.

Well, the MG151, the Hispano II and the MK103 are superior to the 12.7 mm Browning in each of these respects, and have the weight and firepower advantges typical for cannon.

I actually did analyze trajectory - which is given a vastly exaggerated importance in most discussions as realistic firing ranges were 200 - 300 m. The same applies to projectile flight times - effective range against manoeuvring targets is even shorter. Here are some dispersion figures:

MG-FF:             1,0*
MK 108:            1,5*
20mm Type 99-1:    1,5
20mm Type 99-2:    1,5
Ho-1 / Ho-2:       1,5
12,7mm Scotti:     1,6
Breda-SAFAT:       1,7
MG 131:            1,7
20mm Ho-5:         1,9
MG 151/20:         1,9*
MK 103:            2,0*
20mm ShVAK:        2,0
Hispano V:         2,1
37mm M4:           2,1
Ho-103:            2,2
VYa-23:            2,5
12,7mm UB:         2,7
Hispano II:        3,0*
NS-37:             3,3
MG 151:            3,4
,50 Browning M2:   4,0*
Browning ,303:     4,2

* according to historical data - these datapoints were used as a basis for calculation of the rest, see http://www.hitechcreations.com/forums/showthread.php?s=&threadid=131669&highlight=dispersion

>According to your table, wouldnt a B-25H reign supreme, with its 75mm cannon?

Probably not, because the rate of fire is so slow :-)

Regards,

Henning (HoHun)

[Crumpp]

IIRC

From a dead 6 o'clock attack position,  The RAE determined in their FW-190 vunerability analysis that 1 round of .50 cal API had 0 percent chance of:

Penetrating or igniting the Fuel tanks
Hitting the pilot
Hitting the engine
Causing any effective fuselage damage.

From 6 degrees off a dead 6 o'clock .50cal API stood a slight chance of causing effective damage.

20mm on the other hand stood a 50 percent chance of destroying the FW-190 with a one round hit to the correct spot.  20mm stood some chance of destroying the FW-190 from a dead 6 o'clock position from any hits period.  From 6 degrees off dead 6 o'clock these percentages went up astronomically.

Crumpp

[Charge]

"If the 20mm was superior (especially the Hispano) to the .50, why didn't the British and Americans use them for bomber defense?"

Also notice that firing to rear quarter the .50Cal's hitting power increases quite a bit as an incoming enemy fighter will "collide" with the bullet and the same fighter's bullets fired at the bomber have to go sort of up-hill to reach the bomber so the fighter has to have heavier armament than bomber to intercept it efficiently.

-C+

[GScholz]

Originally posted by Charge
Also notice that firing to rear quarter the .50Cal's hitting power increases quite a bit as an incoming enemy fighter will "collide" with the bullet and the same fighter's bullets fired at the bomber have to go sort of up-hill to reach the bomber so the fighter has to have heavier armament than bomber to intercept it efficiently.

-C+

That is a fallacy. The bombers projectiles gets to add the fighters speed, but must subtract the bomber's speed. The fighter's projectiles also gets to add the fighter's speed (since it is firing forward), but must subtract the bomber's speed. So the bomber's and fighter's guns gain an equal ammount of extra energy.

The only difference is added drag for the fighter's projectiles since their speed is greater relative to the air. That speed difference is equal to the bomber's true airspeed.

[Charge]

"The only difference is added drag for the fighter's projectiles since their speed is greater relative to the air."

Exactly. So they slow down more rapidly whereas a rearwards fired bullet has to endure significantly less drag.

If you are near the target the difference is unnoticeable, of course.

-C+

[GScholz]

At 20k+ feet it is also pretty unnoticable at any range. There is nothing "significant" about +- ~200 mph to the drag of a bullet at 20k+.