quote:

Originally posted by Friendly_flyer:
I’m sorry, I wasn’t very clear. The M2 has a low ROF when you include all MGs in the comparison, including cartridge MGs (typically around 800 rounds/min for the M2, 1200 rounds/min for .30 cal (and thereabouts) MGs). The M2 was on par with most .50 cal HMGs, except as you mention, the Berezin. However, the rate of fire of all the non-Berezin HMGs are rather low, my argument is that you need quite a few of them to be effective.

..... I do not desire to start a big argument here, but I consider RoF comparisons between HMGs and rifle-caliber MGs to be of little consequence. The principal consideration is not whether the sheaf of projectiles is the >>most<< dense, but whether it is >>sufficiently<< dense to guarantee effective damage upon a given aerial target. Viewed from that perspective the RoF performance of the M2 was quite satisfactory. It also bears mention that, even allowing for the disparity in HMG versus RCMG rates of fire, the HMG will deliver about 5x the weight of fire per unit of time.

Also, the difference in RoF between the UBS HMG and other HMG models is more incremental than dramatic - perhaps a difference of 10-15 percent. I am of the opinion that overall the UBS was a better and more sensible HMG design for aircraft armament, but that has less to do with its RoF or ballistic performance than it does with its very light weight in relation to the caliber of ammunition it fired.

quote:

The Spitfire was an interceptor rather than an escort fighter, and needed quite a bit more punch than offered by 4 M2s. 6 would be the minimum (and even that would be marginal against a bomber). 6 M2s weigh just a tad more than the late war Spitfire armament (6 M2s weigh 174 kg + ammo, two Hispanos IIs and two M2s weighs 158 kg + ammo). If we are to believe Mr. Williams calculations, you’d need more than 8 M2s to rival the Spitfires firepower, weighing in at 232 kg, and now we are talking weighs that will hit the performance of a plane like the Spitfire.

Despite the M2s many good points, it is not an ideal fighter gun, it’s merely adequate. On the other hand it was reliable (reliability must have been a very important point back then), and more importantly, it was there, with ammo to spare.

..... The question was whether the Spitfire was too small to carry a sufficient number of HMGs. In order to qualify what would have constituted "a sufficient number of HMGs", its intended tactical role must be taken into account. Clearly the Spitfire was designed as an interceptor. But its evolved role, as witnessed in the Battle of Britain, was principally to engage the German fighter escorts while it stable-mate Hurricanes attacked the bomber formations. An armament of 4 x HMG would have been quite suitable for fighter-versus-fighter engagements. A 4 x HMG armament for the Spitfire would also have saved 40 or 50 kilos in weight and represented a weight of fire equivalent of 18-20 x RCMGs.

In addition, while it is absolutely fair and reasonable to say that 4 or 6 HMGs was an inadequate armament with which to engage heavy four-engined bombers, Germany's bomber fleet throughout the war almost exclusively consisted of light/medium twin-engined bombers dfended by RCMGs. American fighters armed with 50cal HMGs had no problems disposing of such targets.

So, I think there are reasonable argument in support of a 4 x HMG armament for the Spitfire. I don't think that an all HMG armament would have made sense for any German fighter, simply by virtue of their need to be able to effectively kill heavy bombers. I don't consider the 50cal to have been a suitable weapon for this role, due to its lack of any useful HE projectile.

This is admittedly a bit of after-the-fact wisdom, but it is IMO nevertheless correct.


Note: RCMG = rifle caliber machine gun

The only HMG that had a lower RoF than the M2 was the Breda Safat construction. All other HMG were about on par or better. This changes when you compare the synced versions, there the M2 is pathetic.

The RoF is about on par with the newer 20mm cannons and considerable better than the older 20mm cannons.

If you were to mount 6xB-20 20mm cannons instead of 8xM2 in the P-47 wing, you'd easily double the firepower for about no penalty, as the B-20 is lighter, has a higher RoF and a more powerful projectile than the M2.

M2 wasn't efficient.

Actually, we're in the position to test these assumptions. If I remember correctly, Olegs damage values aren't that far off from Mr. Williams calculation. A few rounds in quick mission builder with Spitfire Mk.IXe or Mustanng B, C or Mk.III against a Ju 88 or He 111 should give us a few hints.

Maybe the guns are ok, the damage model sure isn't.

quote:

Originally posted by JtD:
The only HMG that had a lower RoF than the M2 was the Breda Safat construction. All other HMG were about on par or better. This changes when you compare the synced versions, there the M2 is pathetic.

The RoF is about on par with the newer 20mm cannons and considerable better than the older 20mm cannons.

If you were to mount 6xB-20 20mm cannons instead of 8xM2 in the P-47 wing, you'd easily double the firepower for about no penalty, as the B-20 is lighter, has a higher RoF and a more powerful projectile than the M2.

M2 wasn't efficient.

..... If one were to ignore the big differences in MV and armor penetration characteristics between the M2 and other HMGs, you might have a point.

Same deal with the Berezin B20. There is ALWAYS a trade-off. The B20 gives up 400+ ft/sec in MV and gives a reduced duration of fire.

But, hey, if you like to believe that the M2 was "pathetic", it's OK with me.

IIRC the M2 would fire 650 to 750rpm, the latter figure was only true if a booster was fitted. I am not sure if this was common or not.

This is an interesting comparison by F. Hahn between the two approaches:

quote:

Originally posted by JtD:
Maybe the guns are ok, the damage model sure isn't.

..... I agree. The kinetic model track with historical evidence, in that 15-30 hits are needed to bring down (as opposed to blow up) an opposing fighter.

But it still lacks the incendiary effect provided by the 50cal API which was in widespread use from the beginning of 1944.

quote:

Originally posted by Friendly_flyer:
Actually, we're in the position to test these assumptions. If I remember correctly, Olegs damage values aren't that far off from Mr. Williams calculation. A few rounds in quick mission builder with Spitfire Mk.IXe or Mustanng B, C or Mk.III against a Ju 88 or He 111 should give us a few hints.

..... I agree. I think it would be very interesting.

quote:

Originally posted by Blutarski2004:

..... If one were to ignore the big differences in MV and armor penetration characteristics between the M2 and other HMGs, you might have a point.

There were big differences? I just do not think so.

IMHO the practical difference between the Browning .50 M2 and other, more modern designs is that the Browning has lower rate of fire and weights about 2-2,5 times as much as other 12,7-13mm guns, or as much as a 20mm cannon. At the same weight and bulk, the cannon is simply a better choice.

quote:

Originally posted by Kurfurst__:
IIRC the M2 would fire 650 to 750rpm, the latter figure was only true if a booster was fitted. I am not sure if this was common or not.

This is an interesting comparison by F. Hahn between the two approaches:

..... The official WW2 RoF figure for the air-cooled aircraft version of the M2 50cal was 750 rpm. With booster, the Rof was 850-950 rpm. Shortly after the war (according to a USAF publication I have) the Rof had been increased to "1200-1500 rpm".

Thanks for posting that comparison page. Did Dr Hahn do a comparison against the Browning 50cal as well?

quote:

Originally posted by Kurfurst__:

quote:

Originally posted by Blutarski2004:

..... If one were to ignore the big differences in MV and armor penetration characteristics between the M2 and other HMGs, you might have a point.

There were big differences? I just do not think so.

IMHO the practical difference between the Browning .50 M2 and other, more modern designs is that the Browning has lower rate of fire and weights about 2-2,5 times as much as other 12,7-13mm guns, or as much as a 20mm cannon. At the same weight and bulk, the cannon is simply a better choice.

..... See my previous post to you re RoF. Regarding weight of the gun itself, it is partly a function of gun horsepower and partly a result of the excessive amount of mechanical life built into the design. I do agree that Berezin 12.7 was a more sensible design from awartime use point of view. It effectively did the same job at considerably less weight. The trade-off was mechanical life, but the design assumptions regarding practical battlefield survival time which underpinned the Berezin design approach were much more sensible than those set down for the M2.

Yup, I cross checked the S.O.C. on the M2, aircraft (air cooled), and indeed its 750rpm base. 850 is given as maximum. 75 rounds may be fired from the standard barrel. After a minute of cooldown allowed, firing can be resumed at rate of one 20 round burst per min. Without long burst, 25 rounds per min is allowed for a long period.

I wonder what was barrel life of the M2, given the above limitations in the S.O.C. IIRC the M3 was introduced post-war with a 1200/min.

No, unfortunately Hahn didnt make any comparisons with the M2. He gives so figures for the price of the MG 151/20 (787 Reichsmark a piece) and the US produced Hispano (708 USD a piece) though.

quote:

Shortly after the war (according to a USAF publication I have) the Rof had been increased to "1200-1500 rpm".

The version with the increased ROF was the M3 fitted in the F-86. ROF (from the US Army) 1150-1250, which is impressive, but rather short of 1500. It is a post war weapon, although its development started during WW2 to improve the aggregate ROF without needing to mount ever increasing number of guns.

M2s averaged around 750 to 800 with booster, with some examples managing 900, but these were worn examples, so accuracy and reliability may have been compromised that much above design ROF.

quote:

Regarding weight of the gun itself, it is partly a function of gun horsepower and partly a result of the excessive amount of mechanical life built into the design

The Russians may well have assumed that building a long life into an aircraft gun when aircraft lasted a relatively short time may have been wasted effort. It depends on the expected lifetime before destruction of a plane. If the plane is expected to make it back then it's worth giving the weapons a longer design life as even if the plane becomes obselete then if the weapon is still current you can put it into a new plane (or give it to the infantry or whatever, which is what happened to a lot of old MG15s, 17s, etc in German service, and a lot of old Lewis and Vickers K observer guns from the RAF, going to the Home Guard and the LRDG respectively).

quote:

Originally posted by Blutarski2004:

Same deal with the Berezin B20. There is ALWAYS a trade-off. The B20 gives up 400+ ft/sec in MV and gives a reduced duration of fire.

The difference in MV is lower, and 3 B-20 weight a lot less than 4 M2, so there is room for plenty of extra ammo. In fact, you'd gain a parity in weight if you were to supply about 300rpg for an about equal firing time, which is about what the US birds carried.

The trade off would be that you couldn't just put a 40 years old weapon into your combat machines but had to develop new ones.

quote:

But, hey, if you like to believe that the M2 was "pathetic", it's OK with me.

I specifically stated this for M2 guns that had to fire through props, where the RoF was about halved for that antique weapon. You know another HMG that cannot get past 400 rpm and still weights 30kg? I know one that managed more than twice that RoF, had an as good projectile and was lighter still. That's like lapping someone 100 times in the course of the Indy 500. Pathetic.

As soon as he said "totally ineffective" he lost all credibility.

quote:

Originally posted by Bremspropeller:
Yep, the cal fifties' superior firepower was the reason why everyone except the god-obeying USAAF (I'm not talking of the USN here..) switched to 20mm

And they tried to but insisted on modifying the Hispano when manufacturing on licence, which already worked but they managed to break. Thus it broke down and broke down and was ready just in time for the war to end. The US Hispano was one of the US cockups of production.

From Wiki: "....The gun was also licensed for use in the United States as the M1, with both the United States Army Air Corps (USAAC) and U.S. Navy planning to switch to the 20 mm as soon as sufficient production was ready. A massive building program was set up, along with production of ammunition, in 1941. When delivered the guns proved to be extremely unreliable and suffered a considerable number of misfires due to the round being "lightly struck" by the firing pin. The British were interested in using this weapon to ease production in England, but after receiving the M1 they were disappointed. In April 1942 a copy of the British Mk.II was sent to the U.S. for comparison, the British version used a slightly shorter chamber and did not have the same problems as the U.S. version of the cannon.

The U.S. declined to modify the chamber of their version, but nevertheless made other different modifications to create the no-more-reliable M2. By late 1942 the USAAC had 40 million rounds of ammunition stored, but the guns remained unsuitable. The U.S. Navy had been trying to go all-cannon throughout the war, but the conversion never occurred. As late as December 1945 the Army's Chief of Ordnance was still attempting to complete additional changes to the design to allow it to enter service.

Meanwhile, the British had given up on the U.S. versions and production levels had been ramped up to the point where this was no longer an issue anyway...."

......And I failed to notice 4 pages where this has already been brought up lol

quote:

Originally posted by JtD:

quote:

Originally posted by Blutarski2004:

Same deal with the Berezin B20. There is ALWAYS a trade-off. The B20 gives up 400+ ft/sec in MV and gives a reduced duration of fire.

The difference in MV is lower, and 3 B-20 weight a lot less than 4 M2, so there is room for plenty of extra ammo. In fact, you'd gain a parity in weight if you were to supply about 300rpg for an about equal firing time, which is about what the US birds carried.

The trade off would be that you couldn't just put a 40 years old weapon into your combat machines but had to develop new ones.

quote:

But, hey, if you like to believe that the M2 was "pathetic", it's OK with me.

I specifically stated this for M2 guns that had to fire through props, where the RoF was about halved for that antique weapon. You know another HMG that cannot get past 400 rpm and still weights 30kg? I know one that managed more than twice that RoF, had an as good projectile and was lighter still. That's like lapping someone 100 times in the course of the Indy 500. Pathetic.

How about 4 x B-20s in place of 6 x M2s for a wing-mounted fighter armament, since US WW2 fighters except P38 carried principally wing-mounted weapons?

4 x B-20s @ 25 kg each = 100 kg
300 x 4 x 0.183 kg = 220 kg
Total Weight 320 kg

6 x M2s @ 29 kg each = 174 kg
300 x 6 x 0.112 kg = 202 kg
Total Weight 376 kg

Makes sense, provided that weight does not need to be added to strengthen wing gun mounts. Although 4 x B-20s only have about 17 pct greater ME than 6 x M2s, the individual B-20 has about 75 percent greater ME than a single M2.

The B-20 fires a VERY light 20mm projectile at 95 grams [which is in part how they get the high RoF and light gun weight]. Just on a W/D^2 basis, its ballistics are actually inferior to the M2 projectile.

The B-20 looks like a very good gun, but there are indeed always trade-offs. The trade-off here is poorer trajectory. If I have some time and can get good estimates on form factors, I'll run a ballistic comparison and see to what extent.

quote:

Originally posted by Blutarski2004:

quote:

Originally posted by JtD:
The only HMG that had a lower RoF than the M2 was the Breda Safat construction. All other HMG were about on par or better. This changes when you compare the synced versions, there the M2 is pathetic.

The RoF is about on par with the newer 20mm cannons and considerable better than the older 20mm cannons.

If you were to mount 6xB-20 20mm cannons instead of 8xM2 in the P-47 wing, you'd easily double the firepower for about no penalty, as the B-20 is lighter, has a higher RoF and a more powerful projectile than the M2.

M2 wasn't efficient.

..... If one were to ignore the big differences in MV and armor penetration characteristics between the M2 and other HMGs, you might have a point.

Same deal with the Berezin B20. There is ALWAYS a trade-off. The B20 gives up 400+ ft/sec in MV and gives a reduced duration of fire.

But, hey, if you like to believe that the M2 was "pathetic", it's OK with me.

JTD just said that the M2 in its synched version that the Rate of Fire was pathetic.

Not the whole gun.