I have a very interesting book which every AHer would do well to read. Maybe you'll agree with its conclusions, maybe you won't, but you can't deny it's got a lot of excellent data. The book is:
Flying Guns: The Development of Aircraft Guns, Ammunition, and Installations 1933-45, by Emmanuel Gustin and Anthony G. Williams, Airlife Publishing Ltd, 2003, ISBN 1-84037-227-3.
Anyway, as the title implies, this book covers all the aspects, not just the guns themselves but also their ammo, which was at least as important, as well as how they were mounted. It's got real convergence settings for a lot of common AH planes, too. Besides describing the weapons and ammo, it also draws on a lot of contemporary test results which compared the effectiveness of various guns and their different types of ammo against targets such as standard self-sealing fuel tanks inside aircraft structures at different ranges, armor penetration at different angles, etc.
At the end of the book, there's an appendix where the authors present their opinions about the relative effectiveness of typical standard gun/ammo combos (because the ammo had such a big effect on what a given gun could do). They even say, "The comparative effectiveness of fighter guns in the Second World War is a subject of perennial fascination (and a great deal of argument) among technical military historians and, in particular combat sim designers and players."
To cut to the chase, the authors crunched the numbers in a way that combines kinetic engergy and ammo chemical energy for a given gun/ammo combo into a unitless coefficient, which can then be compared with the values derived for other weapons. They also arranged their system so that .30cal ball ammo has a coefficient of 1, so it can be used as a baseline for everything else. Interestingly, the authors' formula uses momentum instead of kinetic energy, because in their opinion squaring the velocity overstates its potential to cause damage. Most of the target planes were sheet metal, so extra speed just made a neater hole instead of causing more damage. The velocity was only really important for armor penetration, which is something of a special case on most targets.
Anyway, under the authors' system, things rank as follows:
POWER PER "AVERAGE" ROUND
Takes standard ammo belt composition into account
All .30-ish ball, AP, and I: 1 (.303, .30, 7.9, etc.)
12.7x81SR AP and HE: 3 (Breda-Safat, Ho-103)
13x64B AP and HE: 3 (MG131 and IJN 13mm Type 2)
12.7x99 API: 4.5 (US M2)
12.7x108 API/52: 6 (UB Beresin)
15x96 AP and HE: 7 (MG 151)
20x94 HE and AP: 10 (Ho-5)
20x72RB HE: 12 (MG FF and Type 99-1)
20x99R: 13 (ShVAK and B-20)
20x80RB HEIT and HE(M): 15 (MG FFM)
20x101RB HE: 15 (Type 99-2)
20x82 HET and HE(M): 17 (MG 151/20)
20x125 HE: 18 (Ho-1, Ho-3)
20x110 HE (Mk II and V): 20 (Brit and US Hispanos)
23x152B API and HE: 26 (VYa)
30x90RB HE(M): 58 (MK 108)
37x195 HE: 106 (NS-37)
GUN POWER
Using above standardized ammo combined with guns' stats, such as ROF. All guns rated on UNsynchronized ROF. The authors note that synchronization reductions in ROF varied considerably from about -10% for German electric primers to between -20% to -40% for other systems. The authors give the synchronized ROF for the 12.7 UB, so I've added numbers after the / for synchronized mountings using -10% for German 20mm and -20% for everything else (some of which is unnecessary because some guns weren't synchronized, but WTF?).
.30-ish MGs: 21/17
Breda-Safat: 36/29
MG 131: 45/41
Ho-103: 45/36
.50 M2: 58/46
12.7UB: 102/78
MG 151: 84/76
Type 99-1: 96/78
MG-FF: 120/96
Type 99-2: 120/96
Ho-1 and -3: 126/100
Ho-5: 140/112
ShVAK and B-20: 169/135
Hispano Mk II: 200/160
MG 151/20: 204/184
VYa: 234/208
Hispano Mk V: 240/192
NS-37: 424/340
MK 108: 580/522
It's nice to see the 151/20 and the Hiso2 are about equal in destructiveness, which is supported by the contemporary test data. Basically, the higher velocity of the Hiso was countered by the larger explosive content of the 151/20. So this gives me a bit of confidence in what is obviously a somewhat subjective subject.
The authors take this 1 step further and give a "power-to-weight" ratio, taking into account the weight of the gun and its ammo, to come to an overall efficiency rating for each gun. But that's beyond this argument.
SAMPLE AH PLANE FIREPOWER RANKING
My own creation, based on the above data. This is PER SECOND and AT CONVERGENCE RANGE. The different ballistics of some gun combos on some planes made it harder to get good convergence, and the "sweet spot" was smaller than for more homogenous armaments.
Brit 8x.303: 168
P-40B: 176
A6M2: 226
US 4x.50 (51B, F4F): 232
Bf 109F (1x20mm): 238
La-5: 270
Bf 109E: 274
A6M5: 274
Bf 109G6 (1x20mm): 286
Ki-61: 314
Bf 110C: 324
Yak-9U: 325
US 6x.50 (51D, F6F, Dhog): 348
Ki-84: 352
La-7 (3x20mm): 405
P-38: 432
FW D9: 450
P-47 (8x.50): 464
C.205: 466
N1K2-J: 480
Spit 5: 484
Yak-9T: 502
Il-2M: 510
Spit 9 (2x.50): 516
FW A5 (4x20mm): 642
Bf 109G6 (1x30mm): 662
Typhoon, Hurri IIC, Chog: 800
FW A8 (4x20mm): 858
Mossie: 884
Ta-152H: 948
Tempest: 960
Me 163: 1160
Bf 110G (2x20mm): 1568
FW A8 (2x30mm): 1610
Bf 110G2 (4x20mm): 1976
Me 262: 2320
So, to get back to the start of this thread, 6x.50s, according to this way of looking at things, was a bit weak by European standards, in terms of max potential damage per second. It was better than the anemic guns of the early-war rides, but not quite into the spit and FW class. Still, it wasn't THAT much worse, and the ballistics made for decent accuracy over a fairly long range, plus good convergence from all the guns being the same type. Thus, I feel it was probably easier to get the most out of 6x.50s than it was with the mixed gun types on planes with more powerful armament on paper. This would go some way towards redressing the apparent US weakness. Still, unless you're packing multiple cannon, or a 30mm, you don't have that much firepower.
Of course, I have NO IDEA how HTC models all these guns, and whether or not the above is even close to HTC's method. But at least it puts things in perspective.
