Why did the US ww2 fighters have 50 cals instead of 20mms like their european cousins

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I'm no expert, but the Browning 50-caliber was and is a very effective weapon. Witness the fact that the US Army still uses it in frontline service.
 
MarkS said:
I'm no expert, but the Browning 50-caliber was and is a very effective weapon. Witness the fact that the US Army still uses it in frontline service.
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Several things can be remarked:
- US-produced Hispanos were bad apples
- there was no realistic way for anyone to attack the US with fleet of bombers during the ww2, so the real need for automatic cannon was not there
- dozens of countries use the .50 BMG and other HMGs, but not for arming their fighters now - main platform are vehicles, and main targets are not the enemy's bombers for many decades now
 
pbehn said:
It can be a very interesting discussion involving a lot of science, energy, velocity, rate of fire etc, but could any aircraft withstand 1 seconds fire from 8 x 50Cal or 4 x 20mm cannon?
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If we look at the Whirlwind it had four hispano's or twelve Browning .303's in the nose, if it was available in the BoB it would have made a very effective bomber destroyer either way.
 
PAT303 said:
If we look at the Whirlwind it had four hispano's or twelve Browning .303's in the nose, if it was available in the BoB it would have made a very effective bomber destroyer either way.
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Baders "Big Wing" would have made sense with a couple of squadrons of Whirlwinds.
 
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pbehn said:
It can be a very interesting discussion involving a lot of science, energy, velocity, rate of fire etc, but could any aircraft withstand 1 seconds fire from 8 x 50Cal or 4 x 20mm cannon?
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Assuming all the bullets hit a WW II aircraft odds are severely against it.
Four Hispano guns are equal to 40 rounds in 1 second and since the Germans figured 20 rounds of their 20mm ammo hitting would take out a 4 engine bomber?
104 rounds of .50 cal is also going to make a big mess.
104 Rounds of .50 cal is 4.78kg of metal
104 Rounds of .50 cal is equal to 423 rounds of .303 AP or about 210 AP and 210+ of incendiary. but twelve .303 guns can only deliver about 240 rounds in one second
 
PAT303 said:
The cannon barrels, blisters and stubs all added drag to the Spitfire costing speed, about 10mph or so.
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Wasn't the Hispano with long barrel far more accurate than the German cannon.

I know the Mk 103 with longer barrel was far more accurate than Mk 108 but much heavier.

As an aside not sure Google's advertising algorithm is working for this site as it is trying to sell me a new bikini (here in UK).
 
gruad said:
Wasn't the Hispano with long barrel far more accurate than the German cannon.

I know the Mk 103 with longer barrel was far more accurate than Mk 108 but much heavier.
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There is some confusion here.

Actual "accuracy" doesn't have lot to with barrel length, as in the shells landing in a small area (group).
Practical "accuracy" does have a lot to do with velocity, which translates into short flight time and flat trajectory.
An illustration of the conflict can be seen with the British 17pdr AT gun, Which was pretty good with normal ammo but the APDS ammo, despite very high velocity had rather poor accuracy.

In general higher velocity does give better practical accuracy. Short times of flight means less lead or deflection, which for Air weapons is usually more important than trajectory.

Germans also had several 20mm cannon, The MG 151/20 was slower than the Hispano but it seems have had few, if any complaints about "accuracy".
 
The USN was dissatisfied enough with the 0.5" Browning to field some Corsairs with 4 Hispanos, and evaluated them as roughly three times as effective, i.e., 4 x 20 mm approximately equal to 12 x 0.50". The problem was mostly that US production of the 20 mm for aircraft was botched. Postwar, the USN ditched the 0.50" pretty quickly, with the USAF being a relative laggard.
 
swampyankee said:
Postwar, the USN ditched the 0.50" pretty quickly, with the USAF being a relative laggard.
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Actually in planning, The Navy ditched the .50 cal in the fall of 1944. Either NO or ONE new Navy fighter was ordered after Jan 1945 with .50 cal guns. The first jets were ordered at the end of 1944 and the F7fs and F8Fs were all on order before the turn of the year. Sometimes they kept six .50s on new aircraft to old designs.

The Army on the other hand, was going in a different direction, not really lagging. They were hanging their hopes on the 1200rpm .50 cal gun. (one 20mm was only worth two of them and the weight was a lot closer) and the M23 incendiary bullet was much more destructive and much higher velocity (shorter time of flight) than the WW II ammo.
An F-86 had the fire power of nine WWII .50 cal guns even using WW II ammo.
Trouble was it took years (and 3 different factories) to sort out the M23 ammo and make it more hazardous to the enemy than to the US pilots (only sort of kidding). And by that time even a high velocity, high rate of fire, high chemical content .50 cal system had been passed by.
 
MIflyer said:
A friend told me that the USN found the 20MM guns worked much better if they hot dipped the rounds in wax.

And, given the extensive use of 20MM Orkilien guns on USN ships, they don't appear to have been too upset with them.
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The Oerlikon guns liked greased/waxed/lubricated ammo.
The Hispano's like it too, at high temperatures.
at about 20,000ft on a 59 Degree F (15 C) at sea level you hit about -12 degrees F (-24 C) and waxed/greased ammo doesn't work so well any more

The US took quite a while to use the shorter chambers the British used (by about 1mm) and the grease/wax gave enough resistance to round to allow the firing pin to get a good strike.
There was enough 'give' so that it didn't stop too short in the short chamber, assuming the grease/wax was not as solid as a rock due to low temperatures

The two guns used the same projectiles but they used different cartridge cases and WERE NOT interchangeable.
 
MIflyer said:
A friend told me that the USN found the 20MM guns worked much better if they hot dipped the rounds in wax.

And, given the extensive use of 20MM Orkilien guns on USN ships, they don't appear to have been too upset with them.
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Hispano was firing from the fully closed and locked bolt, so it required that tolerances of the chamber dimensions and ammo dimensions are strictly followed.
Oerlikon fired when the bolt was still moving ('advanced primer ignition'), meaning that even if the length of the chamber and ammo was not in the strict limits, it still worked well.
 
The USN adopted the 20MM Oerlikon at the urging of the British. There was a struggle within the RN over adopting such a radically different weapon from a foreign source that would not be able to provide anything but licensing of the design, and the British wanted the USN to adopt and the weapon so that they could procure them from US manufacturers. The British officer charged with introducing the weapon to the US set up a demonstration firing and was distressed to see that the USN officer assigned to evaluate the gun did not seem very enthused. He suggested the USN officer fire the weapon himself and write his initials in the sky to see how easy it was to operate. The USN officer enjoyed firing the gun and a grin broke out on his face. "Okay, we'll use it!"
The RN officer asked what was the next step in the approval process.
The USN officer replied, "I just decided! That's it!"
The RN initially ordered 100 guns from the US source. And on 8 Dec 1941 the RN officer got a call from his US counterpart., "We are commandeering the entire production run." The USN put over 100 Oerlikons on just one battleship.
 
Will eight .50 cals fit in the nose of a whirlwind?, I think you will struggle getting more than four with ammunition.
 
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