Aircraft gun article

[Tony Williams]

I have posted on my website a new article concerning aircraft guns:

http://www.quarry.nildram.co.uk/CannonMGs.htm (Cannon or machine guns in WW2)

Tony Williams: Military gun and ammunition website and discussion forum

[JAWS2003]

Great article Sir.

[Bronk]

Thanx Tony nice read.  



Bronk

[HoHun]

Hi Tony,

Good article, but the conclusion surprised me:

"To return to the original question, were the Americans right to rely so heavily on the .50 M2 when all other combatant nations had a clear preference for cannon of at least 20 mm calibre? The answer has to be yes. It was adequate for its purpose, and was the only satisfactory aircraft gun in production in the USA."

If the .50 M2 was the only combat-worthy weapon anyhow, why even ask if using it was the right decision? As far as I can see, it was not a decision at all.

Here is a short firepower comparison for roughly equivalent batteries based on energy output as usual:

2x MG 151/20 - 155 rpg - 150 kg - 149% firepower - firepower per weight: 337%
2x MG-FF - 168 rpg - 170 kg - 92% firepower - firepower per weight: 183%
4x MG 151 - 224 rpg - 331 kg - 103% firepower - firepower per weight: 105%
6x ,50 Browning M2 - 250 rpg - 339 kg - 100% firepower - firepower per weight: 100%

Easy to see why the 0.60" MG151 copy was not introduced :-)

Regards,

Henning (HoHun)

[gripen]

IMHO the right question to ask is why the Americans utilized the Browning M2 at so slow rate of fire; the FN version of the Browning M2 did 1100 rounds/min at 1939 ie it had roughly 50% better fire power.

gripen

[Tony Williams]

Originally posted by HoHun
Hi Tony,

Good article, but the conclusion surprised me:

"To return to the original question, were the Americans right to rely so heavily on the .50 M2 when all other combatant nations had a clear preference for cannon of at least 20 mm calibre? The answer has to be yes. It was adequate for its purpose, and was the only satisfactory aircraft gun in production in the USA."

If the .50 M2 was the only combat-worthy weapon anyhow, why even ask if using it was the right decision? As far as I can see, it was not a decision at all.

It wasn't the only choice they could have made: they could have decided to go with the Hispano (in which case they would probably have been forced to make alterations, and suffered reliability problems meanwhile), or they could have pressed on with the .60 MG 151 (not really worth it).

There were various less likely projects as well, such as the .90 (23mm) T1-4 series (heavy and slow-firing).

They could even have decided to follow the RAF's early example and fitted up to 12 .30 cals.

There are always alternatives - frequently, the ones chosen only seem obvious with hindsight.

[Charge]

2x MG 151/20 - 155 rpg - 150 kg - 149% firepower - firepower per weight: 337%
2x MG-FF - 168 rpg - 170 kg - 92% firepower - firepower per weight: 183%
4x MG 151 - 224 rpg - 331 kg - 103% firepower - firepower per weight: 105%
6x ,50 Browning M2 - 250 rpg - 339 kg - 100% firepower - firepower per weight: 100%

Why does 2x151 have the firepower figure of 149% and 4x151 only 103%?
What do you use to determine "firepower"?

-C+

[zorstorer]

Originally posted by Charge
2x MG 151/20 - 155 rpg - 150 kg - 149% firepower - firepower per weight: 337%
These are the 20mm's.....

2x MG-FF - 168 rpg - 170 kg - 92% firepower - firepower per weight: 183%
4x MG 151 - 224 rpg - 331 kg - 103% firepower - firepower per weight: 105%
These are only 15mm.....


6x ,50 Browning M2 - 250 rpg - 339 kg - 100% firepower - firepower per weight: 100%

Why does 2x151 have the firepower figure of 149% and 4x151 only 103%?
What do you use to determine "firepower"?

-C+

[Charge]

Ahh, okay. Didn't notice that missing /20...  


What about "firepower", is that MP?

-C+

[Karnak]

Originally posted by Charge
2x MG 151/20 - 155 rpg - 150 kg - 149% firepower - firepower per weight: 337%
2x MG-FF - 168 rpg - 170 kg - 92% firepower - firepower per weight: 183%
4x MG 151 - 224 rpg - 331 kg - 103% firepower - firepower per weight: 105%
6x ,50 Browning M2 - 250 rpg - 339 kg - 100% firepower - firepower per weight: 100%

Why does 2x151 have the firepower figure of 149% and 4x151 only 103%?
What do you use to determine "firepower"?

-C+

The two guns are 20mm and the four guns are 15mm.

[HoHun]

Hi Charge,

>What about "firepower", is that MP?

It's total power of the projectiless (based on kinetic and chemical energy, the latter calculated from mass of the chemically active content at the energy density of TNT) measured at the muzzle.

The total energy of the ammunition supply of the different batteries is identical. Naturally, the lower-firepower batteries require a longer firing duration to expend ammunition of equal effectiveness.

Regards,

Henning (HoHun)

[HoHun]

Hi Tony,

>It wasn't the only choice they could have made: they could have decided to go with the Hispano (in which case they would probably have been forced to make alterations, and suffered reliability problems meanwhile), or they could have pressed on with the .60 MG 151 (not really worth it).

>There were various less likely projects as well, such as the .90 (23mm) T1-4 series (heavy and slow-firing).

>They could even have decided to follow the RAF's early example and fitted up to 12 .30 cals.

Hm, I don't have the data for the 23 mm cannon unfortunately. I suppose the weapon itself is going to be listed your books, but for a complete comparison I'd need the weight of the belted ammunition, which can be hard to find.

Here is a comparison of the most obvious American options (using 1880 rounds for the 0.50" Browning to reflect the P-51D loadout):

2x Hispano II - 193 rpg - 195 kg - 125% firepower - firepower per weight: 244%
4x 0.60" MG 151 copy - 281 rpg - 373 kg - 103% firepower - firepower per weight: 105%
6x ,50 Browning M2 - 313 rpg - 381 kg - 100% firepower - firepower per weight: 100%
12x Browning ,303 - 782 rpg - 402 kg - 62% firepower - firepower per weight: 59%

To translate that into US terms, replacing the American 50 caliber Browning with British 20 mm cannon would have reduced the weight of the P-51D by 410 lbs (or 4.3% of its loaded weight of 9600 lbs). That's a lot of weight, and as the extra weight is combined with inferior firepower, I really doubt that it was the right decision not to make every effort to get the US production 20 mm cannon into service as quickly as possible.

Regards,

Henning (HoHun)

[gripen]

Well, increasing the rate of fíre of the M2 was an obivious option, it required some modifications and decreased life of the barrel but it was in production and it actually saw some use. For one reason or another it was not  adobted by USAF nor NAVY during war; possibly yet another "not invented here" case again.

gripen

[Tony Williams]

Originally posted by gripen
Well, increasing the rate of fíre of the M2 was an obivious option, it required some modifications and decreased life of the barrel but it was in production and it actually saw some use. For one reason or another it was not  adobted by USAF nor NAVY during war; possibly yet another "not invented here" case again.

It wasn't perfected until quite late in the war, and required so many changes that many parts were not interchangeable. This would have been a pain in wartime.

Tony Williams: Military gun and ammunition website and discussion forum

[gripen]

Actually the FN version of the M2 with 1100 rpm  was a production and combat ready gun allready 1939. Check your mail box.

gripen