Glider said:
A good posting but there are some points which I would comment on.
he British knew before the war that the 303 wasn't powerful enough and undertook some tests for an alternative.
Check your sources. Britian didn't get serious about replacing the .303 until 1940. Experiance showed them 8 x .303's were not sufficient.
Glider said:
The .50 M2 wasn't chosen as it wasn't deemed to be a big enough improvement and the choice was made for the 20mm Hispano. We also knew that it would take time to get it right and a battery of 8 x 303 was sufficient. As we all know experience showed that this was at best a bare minimum but that is with the benefit of hindsight.
The British had no suitable .50 class gun in production. They did have several 20mm's in production of which several were considered and the Hispano was finally chosen. I am quite certain that had the British had a .50 class gun ready to field and facilities for ammo production in 1940 they'd have used it. Since they didn't, they didn't.
Glider said:
At the time the 109 recognised as the major danger was only armed with 3 or 4 LMG's so 8xLMG was a powerful punch for the time particually against planes without armour or self sealing fuel tanks. The P36 of the time had I think 4 xLMG and other USA fighters had similar guns. The italians were arming their fighters of the time with 2 x HMG and the Japenese had 2 x LMG. SO don't be fooled into thinking that we were unconcerned about the firepower needed.
All US fighters ordered for the USAAF and USN from 1937 on mounted .50 class guns.
Glider said:
The DeWilde ammunition used by the RAF and 'borrowed' by the USA was a totally British development. The original DeWilde ammunition was developed in Europe and was the most effective ammo of its time BUT it was impossible to mass produce. We developed our own ammo based on a different principle and put that into mass production however we called it DeWilde as a rather poor attempt at security. It sounds odd I know but it is the real story.
The assistance was in how to mass produce it.
Glider said:
One reason for the USA not developing a reliable 20mm had nothing to do with funding. It was the USA wouldn't put into production the modifications that we had used in the manufacture of our 20mm. If they had it would have worked. Both the USA and the UK started with the same basic gun the French 404 so there is no reason why the changes wouldn't have worked.
The US Hispano was based upon British specs, not French specs. However, the drawings had to be converted to US standards. Unfortunately, some idiot decided that, being a "cannon", the tolerances should be artillary grade, not machine-gun grade, and so the cannons were not very well built. Also the original British specs called for a chamber that was too long - the firing pin would fail to strike the primer hard enough to fire it. These problems was eventually resolved but led to long delays because, amoung other things, the 20mm was not a high priority and did not recieve the kind of funding other weapons systems recieved, nor the best engineers.
Glider said:
Re the ROF I don't see the logic as to why a .50 would speed up after some use whereas every other gun slows down. As automatic weapons are used they settle down and work more efficiently, its the same for every kind of machine. Its why you should run a new car in exactly the same principle. For that reason its why I would stick with the 600rps for the 20 and the 750 rps for the .50 its recognised as the standard figures. All mass produced guns varied in their performance.
Blow back designs tend to increase in RoF when the springs weaken with use. Gas operated guns tend to decreace in RoF as the works get gummed up and the seals become less and less effective.
The only plane for which 750 rpm is quoted is the P-47, at 100 rps. The P-51D, F4U, Hellcat are all quoted at 80 rps from the factory.
80 rps / 6 = 13.333 ; 13.333 x 60 = 800
So 800 rpms is the reasonable figure to use if factory RoF's are to be used. However, in reality the gun fired faster by the time it reached combat.
Glider said:
As for field modifications I wouldn't count them unless all guns had the same changes as standard. I have heard of 20mm increasing their ROF by changes to the gun, but it was powerful enough without them. However most battlefield changes tend to damage reliability. These are precision pieces of equipment and sticking pieces of metal into the workings is unlikely to improve it overall.
The "nickel trick" was the norm for P-51B's in both the 8th and 9th airforce. Armorers and pilots were known to write home asking for nickels for this purpose.
Glider said:
As for the P47 against the B17 again I don't see the logic. The FW190 had far more firepower than the P47. Why would the P47 find it easier than the Fw to shoot down a B17?
Where did I say "easier"?
But, the P-47 does have several advantages. The .50's can be triggered longer than the MG151/20's, giving more chance to slice at the wings. The .50's also have substantially longer effective range. For this kind of target, the .50's would be effective out to over 500 meters, where the MG151/20's were effective to only a little over half that range. Finally, the P-47 has a volume of fire advantage - 100 rps vs. 41 rps.
Glider said:
The example of a bus being destroyed by a .50 is interesting but no more. I have seen a photo of a large tree cut in half by a Maxim in 1895 what does that prove? A 20mm fired at the bus would have blown it to Kingdom come, not just cut in half.
But cutting it in half is all that is needed to down a B-17. Blowing it up doesn't make it any deader.
Also, fusing issues were a real problem for the WWII 20mm. Too often the 20mm would burst on the skin and fail to do any structural damage.
Glider said:
Reliability is something you mention. I have ready loads of articles on air combat and apart from the early days I have not heard anything about the 20mm being unreliable. I do know that the USA held test in which they fired 5000 rounds using a 20 from each manufaturer in the USA plus a British 20mm.
The British 20 firing British ammo fired all 5000 without a failure. The worst American gun had 97 jams in 3,600 rounds after which they gave up with that one. The others did do better, but none made it to the 5000 limit without some jams.
The official jam rate for the British Hispano II was 1:1500 rounds fired during the last 12 months of WWII. For the .50 BMG, it was 1:4000 rounds fired measured in 1942 when the USA entered the war. Steralite lined barrels were introduced in 1943-44, decreasing jam rates.
As I recall, in that particular test the British Hispano suffered about 20 jams in 5000 rounds fired - less than 25% that of US Hispano's tested. Still, 20:5000 is...
1 in 250 !
There are many accounts of Hurc IIc's and Spitfires where all the cannon jammed in a single sortie.
Glider said:
Compare Spit 9 with P51B
2 x 20mm plus 2 x .50 against 4 x .50 No contest.
Remember the USAF considered 1 x 20 to equal 2.5 x 0.50. So using USA figs its comparing 7 x .50 against 4 x .50
The Spit IXc typically flew with 2 x Hispano II's and no mg's. It was a hypothetical comparison anyway.
Besides, the .50's were not generally fired with the Hisapno's - it was one or the other since the trajectories were significantly different.
=S=
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