A basic primer on WW II aircraft guns

[Shortround6]

To avoid clogging other threads I thought I would try to collect the basic differences of WW II aircraft guns in one thread.
Books can and have been written on this subject so this is not an in depth study.

Breaking down the guns into 4 categories.

1, Rifle caliber machine guns. 7.5-8mm
2, Heavy machine guns 12.7-13.2mm
3 20mm cannon.
4 larger than 20mm cannon.

Of the Rifle Caliber Machine Guns (RCMG) most can be lumped together on this basic level.
No major country used a gun under 7.5mm in aircraft despite what their ground troops used which simplifies things.
Most of the guns were similar in size and weight which also simplifies things.
Rate if fire is the only big difference and if we take out the WW I left overs (Lewis guns, etc) and the two really high rate of fire guns, the German MG 81 and the Russian ShKAS then everybody else's RCMGs fall into the 900-1200rpm range which really simplifies things on this basic level.

So, RCMGs, not much difference in power (compared to bigger guns), not much differnce in size/weight and not a lot of difference in rate of fire with the two exceptions above and the MG 81 was pretty much a defensive gun.

Going to the Heavy machine class there are only 4 basic cartridges and 3-4 basic mechanisms amongst the major powers.

German 13 x 64mm round, used by the Germans and Japanese.
British .5 in/12.7x 81 round used by the Italians and Japanese.
The American .50 cal/12.7 x 99mm round which was necked up to 13-13.2 and used by the French, Japanese and a few minor actors.
The Russian 12.7 x108 used by the Russians.

For guns you had;
The German MG 131.
The Russian Berezin UB (and variations)
The Browning used by most everybody else in a variety of chamberings (and a few sizes of gun).
Italians did use one of their own but only in flexible mountings in small numbers.

On a basic level this simplifies things as you have two small cartridges close to each other in power and two large cartridges also close to each other in power.
There is a considerable variation in gun size and weight with weights going from 17kg to 34kg. But excluding the MG 131 and one (or more ) Japanese Navy 13.2mm Brownings just about everything else was from 23-29KG for the bare guns.

Rates of fire (once you get past 1940) went from about 700 -1050rpm with the low being the Italian guns and the high being some versions of the Russian gun.

More later,
Please remember this is basic, there are exceptions to found in small quantities or at the very beginning or end of the war.

 

[GregP]

RCMG's not much difference in power?

Japanese Navy Type 92 flex threw 6.36 kg of mass in 1 second of fire while the Japanese Army Type 100 threw 23.763 kg of mass in 1 second of fire, for a ratio of 3.74 to 1 or nearly 4 times the energy. One did 600 rpm and one did 2,200 rpm.

In the 50-cal / 12.7 mm class, the Browning M2 threw 32.48 kg in 1 second and the USSR's UBK threw 54.6 kg in 1 second for a ratio of 1.68 to 1, or nearly twice the energy. Browning did 850 - 880 rpm and the UBK did 1,050 rpm.

I'd have a definite pick, if that were an option for me. Alas, one was usually stuck with the guns issued in the aircraft they were flying.

But your generalizations are fairly valid except for the extremes, and yet again means that the pilot made the difference most of the time.

 

[KiwiBiggles]

Japanese Navy Type 92 flex threw 6.36 kg of mass in 1 second of fire while the Japanese Army Type 100 threw 23.763 kg of mass in 1 second of fire, for a ratio of 3.74 to 1 or nearly 4 times the energy. One did 600 rpm and one did 2,200 rpm

The Type 92 firing a 11.3 g (about 175 gr) bullet at 10 rounds per second gives a mass throw of about 0.12 kg/s. The Type 100, firing a very slightly heavier bullet (12 g, 190 gr) at 36 rounds per second throws 0.44 kg/s. I suspect your values are for one minute of firing time.

 

[mikewint]

In the 50-cal / 12.7 mm class, the Browning M2 threw 32.48 kg in 1 second

Browning did 850 - 880 rpm

WHOA... Taking the upper rate of fire: 880 rpm that is a per second rate of 880 / 60 = 15 rounds per second.
Next you say that this totals 32.48 kg in ONE SECOND or 71.5 pounds....so a single 50 cal round weighed 2.2 KILOS!! or 4.75 pounds per bullet!!!!
Perhaps you meant PER MINUTE?

 

[Shortround6]

Throw weights have already been addressed.

Japanese type 92 machine gun.

It's a Lewis gun, maybe not an actual WW I leftover but it's a pre WW I design. It also weighs about 8.5KG.

Type 100 machine gun

two barrels and two mechanisms in one housing. it weighs about 16-16.5kg. Each barrel is only firing at about 1100rpm. The feed system is a bit screwy. the 100 round double saddle drum feeds 50 round to each barrel. So the magazine offers about 2.75 seconds of firing time.

These are RCMGs on the fringe.

as far as power goes we can get bogged down in the difference between some of these fringe guns. Everything is relative.

A 20mm Hispano has around 46,900-50,300 joules of muzzle energy per shot and fires 10 shot shots a second, each projectile weighs 128-130 grams.
1.28-1.3 kg per second.

the RCMGs vary from around 3270 to 4300 joules per shot. even at 20 shots per second that is not even equal to two 20mm rounds, weight of metal varied from 9.5 to 12.1 grams per projectile. Again you need 10 or more bullets to equal the weight of one 20mm projectile. Arguing about the difference between the RCMG rounds or the guns that fired them has it's place but doesn't mean much in the overall picture.

As the guns get bigger the variation in the projectiles they fire can also vary a bit more. One has to be careful when comparing some guns that the throw weight (or HE delivered ) isn't computed using the most favorable projectile for the argument of the moment. For instance the Russian 12.7mm ammunition used bullets that varied in weight from 53.8 grams for tungsten cored AP round to 38 grams for an HEI bullet. So what is it's throw weight? 941 grams a second or 665 grams a second or something in between? (used 1050 rpm or 17.5 rps)
Complicating things for the Russian gun (and it was a very, very good gun) is that while if fired at 1050rpm in free mode, it was rarely used that way in fighters. The vast bulk of Russian single engine fighters that used this gun used it synchronized to fire through the prop which dropped the cycle rate to about 800rpm, about equal to the wing mounted free firing US .50 cal guns.
If you are comparing single engine (or single seat) fighter armament this is important to remember. If you are comparing defensive armament of multi seat aircraft (or forward firing armament of multi-engine planes) then the Russians guns show up better than the US gun.

 

[swampyankee]

Tony Williams has a number of articles on aircraft armament; see www.quarryhs.co.uk/miltech.htm for an index.

 

[Shortround6]

Moving on to the 20mm guns (I know I am skipping the German 15mm) we get into a class of guns (and ammo) that has by far the largest variation.

Guns vary from a low of 23kg to a high of 51KG for bare guns, excluding a few fringe guns.
Projectiles vary from 79 grams to 130 grams ( a few fringe guns/ammo types went higher)
Velocities varied from 585m/s to 880 m/s while rates of fire went from 360rpm to 850rpm.

The muzzle energy (in joules) went from 19,700 to 50,300.

Since no gun combined all the worst or all the best we get quite a mixture.

We have the Oerlikon guns which were used by the Germans as the MG/FF and MG/FFM and by the Japanese as the type 99 in several models and by the French as the HS types 7 and 9. These had low rates of fire and used heavy projectiles (until the MG/FFM) but offered low weight (except for the French guns).
The Hispano was developed to improve the rate of fire while not sacrificing the projectile weight or MV of the HS types 7 and 9.
The Germans developed the MG 151/20 which used the projectiles of the MG/FFM at higher velocity and a higher rate of fire. It cost more in weight.
The Russians developed their own gun/s and used lighter projectiles (91-99 grams) to help get a high velocity. They achieved high rates of fire for moderate weight (or low weight in the 1944 and on B-20)
The Japanese, in typical fashion, developed multiple guns and multiple types of ammunition. The Navy Oerlikons have already been mentioned. The Army had some large, slow firing guns with a powerful cartridge, an Oerlikon gun (different ammo than navy?) used for bomber defence and the Browning based Ho-5 that while having a high rate of fire used the lightest projectile.

Categorizing this collection gets difficult as what characteristic do you lead off with?

If we go with power of a single shot then we get 3 groups (with a bit of blending)

the Japanese 20 x 72RB Navy round, the German MG/FF and MG/FFM rounds, the MG 151/20 rounds and Japanese Army 20 x 94 rounds. (19,700 joules to 29,400 joules)

The Russian 20 x 99mm rounds, and the Japanese Navy 20 x 101 mm round are close. ( 35,500-36,600 joules)

The Hispano is pretty much in class by itself, closest round is the 20 x 110RB used in the French HS 7 and 9 guns but lets face it, those guns didn't see a whole lot of use (MS 406s?) (46,900-50,300 joules, HS7&9 42,000 joules)

If we go by rate of fire then we have the roughly 400-500rpm guns, basically the Oerlikons. by who ever used them, and the early Japanese army guns Followed by the 600rpm Hispano, then we have the 700-850 rpm MG 151/20, the Russian guns and the Japanese army Ho-5 gun.

I will try to work out throw weights later, only the MG 151/20, the Russian gun/s and the Japanese Ho-5 can be synchronized.

 

[GregP]

Numbers came from "The Great Fighter Gun Debate," which can easily be found. I suspect you are right about the 1 minute part.

Still, the ratio of mass weight fired per second runs about 4 to 1, so the premise is correct (12.4 for Japanese Type 89 fixed and 45.7 for MG 81: ratio is 3.69). So, there is a large difference in hitting power at the extremities.

Not so much in the middle, as Shortround stated. Again, the pilot would seem to make the difference.

OK, I went back and checked math. I have it right in my tables, but pulled from the wrong column. The actual ratio, low to high is about 4.8 : 1. Still, 12 of 17 guns are in the 10 - 20 g/s range, making them at least comparable, as Shortround said.

 

[tomo pauk]

...
If we go by rate of fire then we have the roughly 400-500rpm guns, basically the Oerlikons. by who ever used them, and the early Japanese army guns Followed by the 600rpm Hispano, then we have the 700-850 rpm MG 151/20, the Russian guns and the Japanese army Ho-5 gun. ...

Let's mention the Hispano V, with uprated rate of fire (750 rpm) and lower weight vs. Hispano II, 42 kg.
MG 151/15 and /20 were good for 700-720 rpm unsynchronised, 650 synchronised.

 

[tomo pauk]

Hopefully this thread will continue

 

[MIflyer]

Were the IJN 7.7MM guns actually firing the same as.303 British ammo? .303 British is also known as 7.7MM, at least according to the packages I have.

 

[KiwiBiggles]

Were the IJN 7.7MM guns actually firing the same as.303 British ammo? .303 British is also known as 7.7MM, at least according to the packages I have.

I think they were a variety of Mauser cartridge.

 

[Shortround6]

"The Great Fighter Gun Debate" The WWII Fighter Gun Debate: Gun Tables
and Anthony Williams site www.quarryhs.co.uk/miltech.htm

Both are both great sites but tend to get complicated rather quickly. For instance the first site has no column or listing of the throw weight per second and jumps to power to weight (muzzle energy per second divided by weight) ratio and mass thrown/fired to weight of gun ratio. While interesting neither figure really addresses the combat capability of the guns as used. As is stated in the text before the tables the projectile weights and muzzle velocities are an average of the available ammunition so small differences should be viewed with caution.

Most of the RCMGs fired bullets of between 10 and 11.5 grams with the French going a bit lighter so figuring throw weight is a rather easy.

US, M2 Browning .30 fires 20 rps and uses 10.7 gram bullets (AP) so the throw weight is 214 grams per second.
British .303 Browning fires 19 rps and uses 11.3 gram bullets (AP) so the throw weight is 214.7 grams per second.
Japanese navy 7.7mm (303) fires 15 rps and uses 11.3 gram bullets (AP) so the throw weight is 169.5 grams per second.
Japanese army 7.7mm fires at 15 rps and uses 10.5 gram bullets so the throw weight is 157.5 grams per second.
German MG17 7.92 fires 20 rps and uses 11.5 gram bullets (AP) so the throw weight is 230 grams per second.
Russian ShKAS 7.62 30 fires rps and uses 11 gram bullets (AP) so the throw weight is 330 grams per second.

All of the above are for the guns when unsynchronized. For comparison the bigger guns go .

German MG 131 fires 15 rps and uses 34 gram bullets (HE) so the throw weight is 510 grams per second.
The American .50cal fires 13 rps and uses 46 gram bullets (AP) so the throw weight is 598 grams per second.
The Russian 12.7mm fires 17.5 rps and uses 52 gram bullets (AP) so the throw weight is 910 grams per second.*1
The Japanese army 12.7mm fires 15 rps (best case) and uses 35.4 gram bullets (AP) so the throw weight is 531 grams per second.

*1- Russian 12.7mm ammo used projectiles as heavy as 53.8 grams and as light as 38 grams for one version of HEI.
Again these figures are for unsynchronized guns.

moving to a few of the 20mm guns for perspective.
The IJN type 99 mod 1 fired at 8.5-9 rps and uses 128 gram shells so the throw weight is 1120 grams per second (average).
The German MG 151/20 fired 12 rps (720rpm) and uses 106 gram shells(average) so the throw weight is 1272 grams per second. *2
Hispano MK II fired 10 rps and uses 128 gram shells so the throw weight is 1280 grams per second.
Russian ShVAK fires 13 rps and used 99 gram shells (best case) so the throw weight is 1287 grams per second.

*2 average of 3 115 gram projectiles and 2 92 gram projectiles as mixed in many belts.

I would note that throw weight alone does not tell the whole story. But it does tend to explain the move to bigger guns.

 

[Shortround6]

I think they were a variety of Mauser cartridge.

The Japanese used an amazing variety of guns and ammo and really make a thread for "basics" complicated

The Japanese Navy used the British .303 round in the Lewis copy pictured above. They also used it in their copy/version of the Vickers gun.

Helping to confuse things the Japanese Army used their 7.7x58SR cartridge in their version of the same Vickers gun.
However both the Army and Navy used the German 7.9mm cartridge in their copies of the German MG 15 which they used in the rear seats of some two/three seat planes. Army also used the 7.9mm in that twin barreled gun pictured earlier.
Japanese navy also used a copy of the German 13mm MG 131 but changed the primer to percussion instead of electric like the German guns.
And then.......................

 

[swampyankee]

The Japanese used an amazing variety of guns and ammo and really make a thread for "basics" complicated

The Japanese Navy used the British .303 round in the Lewis copy pictured above. They also used it in their copy/version of the Vickers gun.

View attachment 483302
Helping to confuse things the Japanese Army used their 7.7x58SR cartridge in their version of the same Vickers gun.
However both the Army and Navy used the German 7.9mm cartridge in their copies of the German MG 15 which they used in the rear seats of some two/three seat planes. Army also used the 7.9mm in that twin barreled gun pictured earlier.
Japanese navy also used a copy of the German 13mm MG 131 but changed the primer to percussion instead of electric like the German guns.
And then.......................

I think it's fair to say that had the IJA and IJN had spent more time trying to cooperate vs trying to one-up each other in their bureaucratic battles, Japan would have been much more difficult to defeat.

Or may not have started the war.

 

[MIflyer]

I wonder how many Aussies tried using the ammo from shot down Zekes in their Enfields?

I recall reading a novel some time back where one character, an Aussie coastwatcher in the Solomans, decried the lack of ammo for his Enfield and had to switch to a Garand.

Y'all might enjoy looking at this. It is a fairly exhaustive work:
Milsurps Knowledge Library - The Machine Gun (by George M. Chinn)

 

[Shortround6]

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.

 

[DarrenW]

This is a very informative thread, thanks Shortround6 for creating it. Do you happen to have any figures concerning how much weight of ammunition the principle WWII fighters could throw at a target when they exhausted their entire ammunition supply? If not it would be fun just to see where each fighter stacks up. Something tells me that the Thunderbolt will land somewhere near the top of the heap.

 

[Shortround6]

As regards to throw weight per second you do have to be a bit careful not to take it to extremes. For example the 75mm gun in the B-25 fired a shell weighing 6,670 grams but it took quite a few seconds to fire round number 2 so the chances of hitting anything in air to air combat were pretty dismal.
Japanese claim to have hit a B-29 with a 75mm gun fired from a KI 109 "fighter" (modified Ki-67 bomber) but that avenue of air to air combat ended at the end of WW II.
you do need a certain number of rounds fired per second to increase the chances of hitting.

 

[DarrenW]

Very good points. I'm just talking in the confines of the weapons discussed so far in this thread. What the single-seaters carried for the most part.....