Performance Comparison: Machine Guns and Light Cannon

[HoHun]

Hi everyone,

Here is a performance comparison grpah based on total muzzle energy (chemical + kinetic) of the guns in question.

This graph covers machine guns and "light" cannon, meaning that cannon up to 23 mm are included and - as single exception - the 37 mm M4 (as used in the Bell P-39 Airacobra) as well because it's poor performance puts it right into the middle of this graph.

Total muzzle energy is based on typical beltings, as far as I could determine what these were. For the 12.7 mm Browning, I have used a pure armour-piercing incendiary loadout.

Guns for which I did not have exact data for the weight of cartridges including belting and thus made a guess at the weight of the belting are indicated by italic names. Guns for which I didn't attempt to make a guess at the weight of the belting and for which the weight data thus probably has to be considered optimistic are indicated by italics in brackets.

The total weight for determining firepower per weight is based on the amount of ammunition equivalent in total energy to 350 rounds of 12.7 mm Browning armour-piercing incendiary ammunition (since this is a typical load-out for aircraft armed with this gun).

Colour coding of the disks is chosen to show nationality of the gun. Colour of the gun designations is chosen for readibility and doesn't code anything.

Any additional data on the guns indicated by italics would be highly welcome! :-)

Regards,

Henning (HoHun)

[Vincenzo]

If i read right the graph the 12,7 Breda Safat has half of power of Browning .50. you can explain why? true the browning has more kinetic energy (maybe ~60%) but afaik the HE load it's in weight near (under 10% more for the Browning)

[HoHun]

Hi Vincenzo,

>If i read right the graph the 12,7 Breda Safat has half of power of Browning .50. you can explain why? true the browning has more kinetic energy (maybe ~60%) but afaik the HE load it's in weight near (under 10% more for the Browning)

I have based my analysis on the data from Tony's site:

WORLD WAR 2 FIGHTER GUN EFFECTIVENESS

(With a very small number of additions and corrections where I thought other data might be more accurate.)

The 12.7x99 API round: 43.0 g, 890 m/s, 2 % chemical content
The 12.7x81SR AP round: 35.4 g, 760 m/s, 0 % chemical content
The 12.7x81SR HE round: 33.0 g, 770 m/s, 2.2 % chemical content

This shows that the chemical content of the 12.7x99 API round is actually greater than the of the 12.7x81SR HE round because the Browning ammunition is larger overall. The heavier mass and the higher muzzle velocity helps the Browning, too.

12.7x99 API round: 17.0 kJ kinetic + 4.8 kJ chemical = 21.8 kJ total
12.7x81SR AP round: 10.2 kJ kinetic + 0 kJ chemical = 10.2 kJ total
12.7x81SR HE round: 9.8 kJ kinetic + 4.1 kJ chemical = 13.8 kJ total

The 0.1 kJ mismatch in the last line is the result of rounding :-)

In addition to the more powerful projectiles, the Browning also fires slightly faster at 13 Hz compared to the Breda-Safat's 12 Hz.

The combined effect of these differences is what you see in the graph, which is based on a pure API loadout for the Browning and a 1:1 mix of API:HE for the Breda-Safat (and the other 12.7x81SR machine guns, too).

If you have data on different projectiles and on real-world belting orders, I could take these into account. All I have on the 12.7x81SR is Tony's table and a page from the US TAIC reports on the Japanese ammunition, from which I have derived the weight of the rounds including belting. (The TAIC data is not yet included above, it has increased the weight efficiency slightly over my "intelligent guess" above. However, the difference was not large enough to do the entire diagram again since that included quite a number of manual steps.)

Regards,

Henning (HoHun)

[Vincenzo]

commonly Breda safat HE load was indicated as 0,8 gr of PETN

add
weight of HE round it's 37,5 grm

[HoHun]

Hi Vincenzo,

>commonly Breda safat HE load was indicated as 0,8 gr of PETN

>add
>weight of HE round it's 37,5 grm

Interesting - this seems to be a heavier bullet than the one listed by Tony.

Do you have the muzzle velocity of this bullet as well? (And maybe a source?)

The belting order typically used by Italian fighters would be nice to know, too - as you can see, a higher proportion of HE projectiles would somewhat increase total muzzle energy.

If the heavier bullet you mentioned had the same 770 m/s muzzle velocity listed by Tony for the HE bullet, its data would be:

Heavy 12.7x81SR HE round: 37.5 g, 770 m/s, 2.1 % chemical content
Heavy 12.7x81SR HE round: 11.1 kJ kinetic + 4.5 kJ chemical = 15.6 kJ total

Still not as much as the 12.7x99 API of the Browning, but a fair increase over the data listed by Tony.

(Were there other types of ammunition besides the AP and HE listed by Tony, by the way?)

Regards,

Henning (HoHun)

[Vincenzo]

there are many ammos can see some here http://www.ww2aircraft.net/forum/wea...s-15397-2.html (The Italian Guns.)

from left ball, tracer, piercing, incendiary, piercing/incendiary
there there is also a pdf with 37,5 grams for HE rounds

here Munizioni inerti cal 12,7x81SR Regia Aeronautica - Munizionamento e ricarica
from left ball, tracer, piercing/incendiary/tracer, piercing/incendiary, HE/incendiary/tracer, HE, HE/incendiary/tracer/selfdestruction

here http://www.gbverrina.net/SITO/Militaria/12,7breda.htm
info on HEIT round 37,5 grams and 0,6 gr of filling


p.s. unlucky nothing on velocity

[HoHun]

Hi Vincenzo,

>p.s. unlucky nothing on velocity

Hm, this makes it difficult to calculate effectiveness, I'm afraid. But interesting to see the different projectile types!

With regard to the belting order: I have not yet seen anything definite on the 12.7 mm Browning either.

Sweb in one post here on this board suggested that API and Ball was used at least by one specific pilot.

Jabberwocky suggested that the belting mix was one Tracer, two AP and two API in each five rounds.

Both combinations would probably adjust the effectiveness of the 12.7 mm Browning somewhat downwards, but I admit I haven't seen any good data on the tracer round.

Regards,

Henning (HoHun)

[Vincenzo]

also italian belt was not all HE rounds

[Vincenzo]

HoHun please can make a table with power of guns, and can add used Hz?

[HoHun]

Hi Vincenzo,

>also italian belt was not all HE rounds

I have used 1:1 HE:AP for the comparison. This seemed like a conservative guess in the absence of real-life data.

Regards,

Henning (HoHun)

[HoHun]

Hi Vincenzo,

>HoHun please can make a table with power of guns, and can add used Hz?

Grr, bloody Excel crashed on me while I was still trying to make a monotype table, working around the bloody incompetent internal formatting functions. So here is the debris I managed to salvage ...

Gun                 Cartridge                E     f     P
Type                Type                    kJ    Hz    MW
MK 213/30           30x90RB              460.2   19.  8.74
MK 108              30x90RB              460.2   10.   4.6
MG 151/20 (MX)      20x82                116.9   12.   1.4
Hispano V           20x110               102.9   12.  1.23
MK 103              30x184B              401.2    7.  2.81
MG 151/20           20x82                 95.7   11.  1.05
VYa-23              23x152B               133.    9.   1.2
MG-FF/M             20x80RB               97.5    9.   .88
Hispano II          20x110               106.2   10.  1.06
Ho-301              40 mm CL              302.   7.5  2.26
NS-37               37x195               542.5    4.  2.17
Berezin B-20        20x99R                49.5   13.   .64
Ho-1 / Ho-2         20x125                 92.    7.   .64
12,7mm UB           12,7x108              28.1   13.   .37
20mm ShVAK          20x99R                49.5   13.   .64
20mm Type 99-1      20x72RB               65.6    8.   .52
37mm M4             37x145R              362.4   2.5   .91
20mm Ho-5           20x94                 50.5   14.   .71
20mm Type 99-2      20x101RB              78.6    8.   .63
MG 131              13x64B                 14.  15.3   .21
MG 151              15x96                 38.1   11.   .42
,50 Browning M2     12,7x99               21.8   13.   .28
MG 17               7,92x57                5.4  16.7   .09
Ho-103              12,7x81SR              12.   15.   .18
Browning ,303       7,7x56R                3.7   20.   .07
12,7mm Scotti       12,7x81SR              12.   12.   .14
Breda-SAFAT         12,7x81SR              12.   12.   .14

Looks a bit ugly but has all the data. I'm going to leave it like that because else I'd have to start over, and I don't enjoy formatting.

P = E * f

E and f are average values since each round has its own E and possibly f. The German guns deviate a bit from Tony's figures, mostly downward.

Regards,

Henning (HoHun)

[Vincenzo]

thanks

[HoHun]

Hi again,

>The TAIC data is not yet included above, it has increased the weight efficiency slightly over my "intelligent guess" above. However, the difference was not large enough to do the entire diagram again since that included quite a number of manual steps.

Since a fellow forum member provided information on the 1941 Hispano belting order - usually 2:2 armour piercing:ball - as well as information on the AP and Ball rounds, I have now updated my comparison diagram, including the TAIC data ... here it is!

Regards,

Henning (HoHun)

[HoHun]

Hi again,

>The 1941 Hispano belting order - usually 2:2 armour piercing:ball

Slight correction: I meant to write "high explosive:ball". The above diagram is correct, though.

(I'm told the belting order in 1941 was not firmly established and different variants were tried, with high-explosive/incendiary being used when it came available and finally - in 1942, according to Tony - armour-piercing incendiary to replace the ball rounds in 1942. Maybe a 3:1 high-explosive:ball mix was even more typical in 1941 than the 2:2 mix I included.)

Regards,

Henning (HoHun)

[Vincenzo]

you included TAIC data but my eyes don't see different.. so taic data were not much different from Tony's data