A basic primer on WW II aircraft guns

Shortround6 said:

View attachment 483302

Click to expand...

I just wanted to point out that the caption in the image isn't entirely correct.
The A6M2 Model 21 actually carried about 690-700 rounds per gun IIRC.

- Ivan.

Well, it's not just weight of fire. Kinetic energy is important, too. Otherwise we'd be firing bowling balls.

Many years ago I sat down with a copy of Gun Digest and did some calculations based on the ammo data. Turns out that because the thirty ought six round was more powerful than the .303 and the .50 cal round a whole lot more powerful than the .303, the two fifties and four .30 cal guns of the early P-40 and P-39 put out a great deal more kinetic energy than did the eight .303 guns of the British fighters.

I would guess that the eight (or twelve) .303 guns of the RAF fighters were better for strafing ground troops and reports from Burma where this was done quite a bit tend to confirm that.

Needless to say, the eight .50 cal guns of the P-47 and strafer B-25's put them in a whole another world when it came to firepower.

MIflyer said:

Well, it's not just weight of fire. Kinetic energy is important, too. Otherwise we'd be firing bowling balls.

Many years ago I sat down with a copy of Gun Digest and did some calculations based on the ammo data. Turns out that because the thirty ought six round was more powerful than the .303 and the .50 cal round a whole lot more powerful than the .303, the two fifties and four .30 cal guns of the early P-40 and P-39 put out a great deal more kinetic energy than did the eight .303 guns of the British fighters.

I would guess that the eight (or twelve) .303 guns of the RAF fighters were better for strafing ground troops and reports from Burma where this was done quite a bit tend to confirm that.

Needless to say, the eight .50 cal guns of the P-47 and strafer B-25's put them in a whole another world when it came of firepower.

Click to expand...

Hello MIFlyer,
The British probably agreed with you because the while the Spitfire Mk.IXc had 2 x 20 mm and 4 x .303, the Mk.IXe replaced the .303s with a pair of .50 caliber Brownings.

When comparing energy, one has to also consider at what range the target will be. At the muzzle, the .30-06 has more energy, but at a distance, the .303 British typically retains velocity better because the bullets tend to be heavier and with a boat tail. In addition, military .30-06 tends to run a bit less velocity than commercial .30-06, so Gun Digest may not be the best reference.

- Ivan.

I think the biggest missed opportunity in WWII aircraft guns was that the US refused to develop a 20MM version of the .50 cal, the experts saying it would not work. The Japanese did not know that and went ahead and did it. At the Smithsonian they have a US .50 cal and a Japanese HO-5 20MM cannon sectioned and sitting side by side.

going on to the big guns we have,

one/two 23mm guns in common use,

two 30mm cartridges in common use,

two 37mm guns in common (somewhat) use in air to air combat.

There were other guns but only in small numbers or for ground attack.

Now here it is good to remember the cube rule of gun design. As a very rough guide for guns of similar purpose the weight of a projectile and the needed gun go up with the cube of the caliber. a 20mm gun would fire a projectile about 15 times heavier than an 8mm gun if the projectiles were of similar construction and shape. a 23mm gun would fire one roughly 50% heavier than a 20 mm and a 30mm gun would fire one about 3.375 times as heavy as a 20mm.
They can a did play games with both shell shape/construction and with gun velocity/rate of fire to keep gun weight down, but large guns and ammo get very large and heavy very quickly.

The Russians were the only users of the 23mm in quantity, others had prototypes as it was an attractive caliber (useful increase in size of projectile whie still staying close in gun size).

The most common 23mm gun was the Russian VYa used mostly in the IL-2 for ground attack. It was large heavy gun (68 kg) that fired at 550-600rpm at high velocity (880m/s) with 200 gram shells. It may have been trialed in through the prop installations but was not very successful at it. It used 23 x 152
ammunition

The second Russian gun/cartridge was the 23 x 115 NS-23 although there is little agreement as to how much service it actually saw in WW II.
To go with the smaller cartridge case it used a lighter projectile (in some forms) and lower velocity (690m/s) that allowed for a smaller,lighter gun.

The Germans used a long 30mm, the 30 x 184B in two guns, the MK 101 and the MK 103 but on a basic level the 103 is just a faster firing/lighter 101.
However we are no getting into the drawbacks of big guns, Firing 330-500 gram projectiles at 690-940m/s requires large guns (180-141 kg ) and low rates of fire, 230rpm for the MK 101 and 360-420 for the MK 103.

The MK 108 used a much shorter, lower powered round (330 gram projectile at 505m/s) that allowed for a smaller (60kg) gun and higher rate of fire (600-650rpm) This was the gun in the 109, under the wings of some FW 190s, in the nose of the me 262 and in many other installations.

The 37mm guns are the US M4 gun used in the P-39 and P-63. A 96 KG gun it fired 608gram HE shells at 610m/s at a cycle rate of 140-150rpm (at best)

The Russian 37mm NS-37 was a 170kg gun that fired 735 gram HE shells at 900m/s at a cycle rate of 250rpm (?). The 37mm gun used in the post war jets was lighter, used a lower powered cartridge and fired faster.

Obviously mounting big guns required both proper planing and sacrifices somewhere in the plane's design/performance.

Shortround6 said:

I first read that book in my teens from the local library. Prices for print copies kept me from buying it.
A lot of good information and the sections on the American high rate of fire .50 cal and the high velocity .50 and .60 cal guns sure show that the Americans weren't sitting back complacent with the the standard .50 cal gun.
They also show that designing and building high performance guns is neither quick or easy.

Click to expand...

The Navy, at least, was trying to get 20 mm guns into its fighters, but the problem seemed to be incompetence by the US manufacturing and procurement system. From what I've read, the USN determined the 20 mm was much more effective than the 0.50". The USN ditched the 0.50" pretty quickly post-war.

MIflyer said:

Well, it's not just weight of fire. Kinetic energy is important, too. Otherwise we'd be firing bowling balls.

Many years ago I sat down with a copy of Gun Digest and did some calculations based on the ammo data. Turns out that because the thirty ought six round was more powerful than the .303 and the .50 cal round a whole lot more powerful than the .303, the two fifties and four .30 cal guns of the early P-40 and P-39 put out a great deal more kinetic energy than did the eight .303 guns of the British fighters.

Click to expand...

Here we start getting into details. All of the figures I have given so far are for guns that are "free firing", that is not hindered/restricted by synchronizer mechanisms.

I have two figures for British .303 ammo for energy. 3280 joules for the AP round and 2730 joules for the Incendiary round. averaging them together and multiplying times 19 for rate of fire time 8 for the number of guns and we get 456760 joules per second.

for the long nose P-40 the .30 cal guns (which used boat tail bullets or AP for the most part that was 168-173 grains and not the 150 grain flat based bullets used in the rifles) we have 3890 joules for the AP round and 4050 joules for the M1 incendiary round. which gives us 317600 joules for the four wing guns.

The two cowl guns however have ammo that is listed at 16,600 joules for the incendiary (M1) and 17,400 joules for the M2 AP.
Unfortunately the the synchronized cowl guns have rates of fire of about 450rpm, instead of the 600rpm of a free firing gun in 1940/early 41. Which gives an energy figure of 255000 joules per second for a total of 572600 joules per second, or about 25% greater than the British eight .303s.

Yep, that's right. The two .50 cal cowl guns overwhelm the eight .303's in terms of energy.

What I don;t think we can quantify easily is
1. Range. The .50 cal is virtually a sniper round.
2, Penetration. What does the round do when it hist armor, an engine, etc.

And of course there was API ammo, which greatly increased the lethality of the .50 cal. There are reports of Hellcats being down to almost no guns working, hitting a Val with a single .50 cal round and that setting it on fire.

Ah no. the total of all six guns on the P-40C/Tomahawk was 25% greater than the eight .303 guns.

The two cowl .50s had 56% of the energy of eight .303s or roughly one cowl .50 was slightly better than two wing mounted .303s.

of course the ratio changes when the .50s get put in the wing and their rate of fire goes up to 600rpm and the ratio changes again when the rate of fire is increased to 800rpm.

I am afraid the .50s vaunted reputation as a sniper round does little good in air to air combat. A 300mph airplane is moving 440feet per second and any time of flight of a projectile, regardless of shape and size, that approaches even 1 second let alone 2 simply introduces too much error in aiming.

The M8 API projectile was not introduced until about 1943 so what ever it's benefits in 1943/44 it didn't exist in 1940-41-42.

Hi Shortround,

I like where you are headed with this calculation. Being an engineer, I tend toward doing that, too.

Just for fun, the energy you calculate above is muzzle energy, not energy at impact. I'd think that while no two shells are likely exactly the same in air resistance (and perhaps other ballistic characteristics), they are close enough that energy dissipation within ... say ... 200 yards or meters SHOULD be quite close to one another. I am thinking of energy at the point of convergence for wing-mounted guns. Fuselage-mounted guns do not converge, so that is not a factor. But MOST shooting will likely take place in and around the point of convergence since the guns would normally be set to converge at a likely target distance. My bet is most pilots shooting fuselage-mounted guns are at similar ranges.

But energy at 1,000 yards or meters could be quite difference, especially for bigger rounds in cannons.

So, I was wondering where you are taking this calculation. Is it a comparison of muzzle energy, an eventual lethal range calculation, or perhaps something else? Or just for fun? Digging into data is fun!

Just to share, I attached my file on aircraft guns, mostly but not entirely gotten from the Great Fighter Gun Debate. I didn't take their word for it and calculated the formulas myself, and added a column or two as well as muzzle energy in Joules and high, average, low plus high and low 1-second mass of fire.

In the cannons, I'd LOVE to add a calculation for explosive energy added to kinetic energy per round. If anyone has those data and would share them, thanks you in advance.

Also, we have a Bf 109E at the museum that as shot down in Russia. I have not been all that curious as yet, but I will go look hard at it this weekend and see how many holes are in it and what the likely caliber is. I am assuming that since it is an early model (an E), that it was likely shot down by an LaGG-3 or other early-opposition fighter. At least we'll have some idea of how many hits it took to bring it down.

Shortround6 said:

The Germans used a long 30mm, the 30 x 184B in two guns, the MK 101 and the MK 103 but on a basic level the 103 is just a faster firing/lighter 101.
However we are no getting into the drawbacks of big guns, Firing 330-500 gram projectiles at 690-940m/s requires large guns (180-141 kg ) and low rates of fire, 230rpm for the MK 101 and 360-420 for the MK 103.

The MK 108 used a much shorter, lower powered round (330 gram projectile at 505m/s) that allowed for a smaller (60kg) gun and higher rate of fire (600-650rpm) This was the gun in the 109, under the wings of some FW 190s, in the nose of the me 262 and in many other installations.

Click to expand...

GregP said:

...
Just to share, I attached my file on aircraft guns, mostly but not entirely gotten from the Great Fighter Gun Debate. I didn't take their word for it and calculated the formulas myself, and added a column or two as well as muzzle energy in Joules and high, average, low plus high and low 1-second mass of fire.

Click to expand...

The Fw 190 often carried the MK 108 in the outer wings.
Let's put the myth of the over-weight MK 101 to bed. Empty weight 139 kg. Translation by your's truly:

GregP said:

Hi Shortround,

I like where you are headed with this calculation. Being an engineer, I tend toward doing that, too.

Just for fun, the energy you calculate above is muzzle energy, not energy at impact. I'd think that while no two shells are likely exactly the same in air resistance (and perhaps other ballistic characteristics), they are close enough that energy dissipation within ... say ... 200 yards or meters SHOULD be quite close to one another. I am thinking of energy at the point of convergence for wing-mounted guns. Fuselage-mounted guns do not converge, so that is not a factor. But MOST shooting will likely take place in and around the point of convergence since the guns would normally be set to converge at a likely target distance. My bet is most pilots shooting fuselage-mounted guns are at similar ranges.

But energy at 1,000 yards or meters could be quite difference, especially for bigger rounds in cannons.

So, I was wondering where you are taking this calculation. Is it a comparison of muzzle energy, an eventual lethal range calculation, or perhaps something else? Or just for fun? Digging into data is fun!

Just to share, I attached my file on aircraft guns, mostly but not entirely gotten from the Great Fighter Gun Debate. I didn't take their word for it and calculated the formulas myself, and added a column or two as well as muzzle energy in Joules and high, average, low plus high and low 1-second mass of fire.

In the cannons, I'd LOVE to add a calculation for explosive energy added to kinetic energy per round. If anyone has those data and would share them, thanks you in advance.

Also, we have a Bf 109E at the museum that as shot down in Russia. I have not been all that curious as yet, but I will go look hard at it this weekend and see how many holes are in it and what the likely caliber is. I am assuming that since it is an early model (an E), that it was likely shot down by an LaGG-3 or other early-opposition fighter. At least we'll have some idea of how many hits it took to bring it down.

Click to expand...

Hi Greg,

SR6's analysis may be difficult to replicate for what you ask for as there are far too many variables involved. Let's say for instance we took 300 meters as the measurement (many wing mounted guns converge at this distance; but of course, that is not a given as an individual pilot could change to his liking).
Then one has to have the ballistic coefficient of each projectile to correspond with muzzle velocity to get an idea of energy loss at a given distance. But this will always be different at different altitudes and barometric pressures and relative humidity... see where I am going? So while the difference in .30-06 and .303 is so nominal as to not really be worth the effort to work out the comparison, the .50 cal is going to retain more of its energy and will have an even greater advantage over distance than at the muzzle. In any case, at the muzzle gives the most consistent comparison even if it is not the most relevant.

Hi Tomo,

Got the numbers from the Gun Debate Table, not from personal measurement.

Since you are generally spot on,. I have updated my table for the Mk 101. Anyone else can do the same for themselves in Excel. Naturally, it changes the Soviet Q factor, but not the projectile weight, rate of fire, or mass thrown.

Thanks for the correction. I have the gun data but have never really gotten into examining it mainly out of more interest in other topics, not from lack of interest in guns.

Cheers.

Greg - not my measurement, simply what is stated in the manual
Thanks for the Excel table. Seems like the MK 101 weight is still at 180 kg.

tomo pauk said:

Let's put the myth of the over-weight MK 101 to bed. Empty weight 139 kg. Translation by your's truly:

Click to expand...

Thank you. I will note however that the 6 round box magazine, empty seems to weigh around 7.5 kg and the 30 round magazine around 19.5kg if we subtract the weight of the ammo from the weight of the gun with the loaded magazine/s.

I would note however that the British/American Hispano also needed either a drum or a belt feeder that weighed almost the same as a drum but neither are usually listed in it's weight either.

Shortround6 said:

Thank you. I will note however that the 6 round box magazine, empty seems to weigh around 7.5 kg and the 30 round magazine around 19.5kg if we subtract the weight of the ammo from the weight of the gun with the loaded magazine/s.
...

Click to expand...

6rd box was at 'about 6.2 kg', drum was at 'about 18.2 kg'.

tomo pauk said:

Greg - not my measurement, simply what is stated in the manual
Thanks for the Excel table. Seems like the MK 101 weight is still at 180 kg.

Click to expand...

Yes, I changed it locally on my own system only. But, if you can open the file posted, then you have Excel and can simply changed the weight yourself in the spreadsheet. I have a LOT of data in Excel, and like to keep on top of it. This small file is an update of some data I got maybe 10 - 15 years back when I ran across the Great Fighter Gun Debate website.

Keeping track of it is getting to be a chore!

Cheers.

As far as striking energy goes, it becomes a tar pit of complication as so few rounds show the same decrease in velocity over distance. Over 100-200 yds we may be able to make some assumptions but by the time you get to 300 meters things can get very different. However this is at sea level and at 20,000ft or so where the air is roughly 1/2 as dense the rounds are going to show a lot less difference.

However, and the figures for the German rounds and the allied rounds were from different tests even if both German.
At sea level the 20mm Hispano lost about 23% of it's velocity by 300 meters.
The US .50cal lost about 15%
The German 7.9 lost about 33%
The German 13mm lost about 33%
The German 15mm lost about 23%
The German 20mm mine lost about 38%
The German 20mm 117 g lost about 23%
The German 30mm mine lost lost about 26%

Now some of these projectiles started at widely different velocities.

For the German guns the actual times of flight to 300 meters varied from 0.357 seconds for the 15mm gun to 0.696 seconds for the 30mm mine shell.
While much is made of the Germans use of fuselage mounted guns they threw much of that advantage away by using different guns with different ballistics and even some of the shells mixed in the same belts/drums of the 20mm cannon show significant differences in flight times at 300meters. While the 92 gram mine shell starts out faster it looses velocity so fast that the slower 117 gram projectiles (which often made up 60% of the belts) wound up passing them out.

At close range it makes no difference and there may be a sweet spot further out (or blending?) but for long range shooting the set up was pretty lousy.

I don't get too excited by the difference in trajectory as planes are pretty big targets compared competitive shooting or even deer hunting so by the time you have to worry about the shells falling below the target you need to be leading the target by multiple plane lengths (like over 5) so that becomes the bigger error.

Was just wondering, Shortround. Was going to offer to help calculate data.

Since you seem to have a lot of this data, you KNOW it isn't easy t find in electronically-readable format. Most has to be hand entered. I have done a lot of that, but make some data entry errors, as we all do from time to time. Much better to use OCR, if possible ... but not always possible.

Cheers.

Nice work guys. Very interesting and absorb-able. keep it going pleaae.