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For some air forces you have to balance out the weight of the gun and ammo ( one .50 round weighed about 5 times what rifle caliber ammo did) against what engines they had available. A lot of the early American aircraft with 1000-1200 engines suffered from being saddled with too much weight of guns and ammo.
From here.Claims that the ammunition of the Ho-5 was downloaded to solve reliability problems appear to be incorrect. According to Col. Okamoto, the gun was designed for a muzzle velocity of 750 m/s, and both wartime and post-war US source specify it as 2400 to 2500 fps, i.e. 730 to 760 m/s. Col. Okamoto does not mention downgrading of the ammunition. (Ted Bradstreet)
The Americans and Soviets never came up with exploding ammo (or even high capacity incendiary ammo) for their high velocity 12.7mm guns. I am not sure why. Germans, Italians and Japanese did for their lower velocity 12.7-13mm guns. Japanese had trouble with prematures. It could be they didn't want to bother with fuses that small. It could be that the higher velocity and higher pressures acting on the base of the projectiles required stronger construction, cutting down on an already low HE content. I don't know.
The lighter Japanese Army adaptation is indeed interesting, though so is the heavier 13.2 mm Japanese Navy one, and more so the sheer breadth of developments into cannons the Japanese Army managed. It shows a potential for the basic design that everyone else (even its original designers) apparently missed. (though at one time on the forums here there was mention of a .60 cal US adaptation of the browning -not the T17 MG 151 copy- but I never got more definite details on this, though the mention seemed to imply it was a direct adaptation of the existing gun and ammunition case necked out to .60 cal and presumably firing at a somewhat lower velocity)Scaled down to take the British/Italian/Japanese 12.7mm round it might have done fairly well for some nations. Scaled up it might also have done OK. Japanese had quality control problems and material shortages and the Browning didn't tolerate either one very well.
From most of what I've seen on the topic, the Japanese Browning adaptations would have indeed progressed more smoothly (and been more reliable) if not for their material and quality control shortcomings. (ie if similar developments had taken place in the US or UK, for example)The P-39 might've benefited with 3 'cannoncinos' only; synchronization kills Rof down to 500, so it would be 800 + 1000 rpm for the trio. Maybe adding another one synchronized, between the two? Wing guns ammo deleted, of course. The P-38 with 5, P-47 with 6, remainder of S-E fighters with 4?
In case British decide to make the 18mm, 4 for Hurri and Spit? Or 2 of those, plus 4 MGs in time of BoB?
Germans - 2 for Bf 109E (HMG for the earlier versions), the 3rd added in central position? 4-6 for the Fw 190?
Re. Ho-5: looks like the gun was okay from get-go:
From here.
With anything below 15 mm, the consensus generally seemed to be that HE rounds were ineffective given the limited capacity and space occupied by fuzing. (with mine shells, the 13 mm german ammunition might have been an exception, particularly with HE/I loadings broadening effectiveness) There's the possibility of using unfuzed rounds filled with sensitive high explosive intended to detonate on contact (I believe some .30 cal ammo used PETN filler for this reason), but incendiary fillings seemed to be considered more effective there too. (particularly incendiary fillings that also had low-explosive impact properties -various flash-powder like aluminum/magnesium + oxidizer compositions that acted as contact/impact explosives and incendaries, though I believe De Wilde used nitrocelulose to similar effect)I imagine they came to the conclusion that the effectiveness of an explosive .50-calibre round wasn't worth it. Using the British 'de Wilde' incendiary was a much better choice in my opinion.
Not sure what the Russians used.
OK, that's what I'd thought ... barium nitrate flash powder composition that ignites/explodes on impact. What threw me was wiki's article detailing the Mk.VI incendiary as using nitrocellulose Incendiary ammunition - Wikipedia, the free encyclopedia it seems trying to refresh my memory on the subject misinformed me as that article only lists the failed Mk.VI and not the Mk.V or Mk.VII using Dixon's barium nitrate design. (the Mk.VII is the one I particularly remember as it's rather well illustrated in the Incendiary B Mark I.z .5" vickers round)'De Wilde' was magnesium/aluminum alloy (50%), barium nitrate (50%)
Correct, the Mk.V was a fuzed explosive/incendiary round deemed too complex and costly to mass produce.The Mk.VI round wasn't failed at all. That was the initial 'de Wilde' incendiary that made it just in time for the Battle of Britain and was highly sought after by pilots.
The Mk.V is probably what you are referring to. I can't recall details on it - in any case the design either wasn't adopted or saw very, very little service.
All military guns/cannon in the modern world were using smokeless powder by that time, the British mostly using Cordite, a double-base propellant with a high fraction of nitroglycerin combined with nitrocellulose and a small portion of petroleum jelly. Alternate loadings seem to have included granulated single-base nitrocellulose powders, presumably with some sort of stabilizing agent.All British ammunition used in aircraft used nitrocellulose propellant, and this is probably where the wiki contributor became confused.
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The Americans and Soviets never came up with exploding ammo (or even high capacity incendiary ammo) for their high velocity 12.7mm guns. I am not sure why. Germans, Italians and Japanese did for their lower velocity 12.7-13mm guns. Japanese had trouble with prematures. It could be they didn't want to bother with fuses that small. It could be that the higher velocity and higher pressures acting on the base of the projectiles required stronger construction, cutting down on an already low HE content. I don't know.
Part of the answer for the above question is that US went to either combine MGs with a cannon, or went to 6-gun batteries (or more); works well with plenty of installed HP, bad with 1000-1200 HP on-board. Soviets were more interested in cannons, 20/23/37 mm, even 45 mm. The low 'bang-for-buck' of exploding .50 ammo is surely an issue, eg. the Germans didn't bothered much even with MG 151 and went fast to the 20 mm variant.
The .50 was cursed not only with it's own weight but it's heavy ammo. A single round goes about 112grams compared to the 162 grams to over 250grams for 20mm ammo. Unfortunately the only common 20mm round that weighs twice waht a .50 cal round does (or a bit more) is the Hispano. The German, Italian and Japanese 12.7-13mm rounds were about 70-75% of the weight and some of the lighter 20mm cannon rounds were only about 65% heavier.
It was surely a heavy powerful round. Hence my proposal for necking it out. Yes, the weight would go up to around 150 grams, but a fighter that carried, say, 6 x 350 rds, will now be carrying 4 x 350 (or 400) rds, along with 2 guns less; we even cut the drag a tiny bit.
Compared with Hispano II (50 kg), the weight of two '18mm' should be ~60 kg. Where 150 rds of Hispano ammo are carried, 250 rds of the 18mm might go instead (weight-wise). The MV should be lower for the proposed gun, but RoF should go to 3200 rpm for 4 of them, vs. 1200-1300 for the Hisso II. Hispano would fire a more powerful shell, 130 g vs. ~80 g.
For the Germans, the proposed gun would've been fitted more easily in the wings of the Bf 109 than a 'full power' 20 mm cannon, and contrary to the MG FF it would be belt fed. That would also allow to get rid of the cowl LMGs/HMGs.
Since the gun muzzle would be either not protruding, or just a little bit protruding, that would cut a drag a bit vs. a muzzle sticking out a foot or like.
The American .50 also does not play well with others
While it is a pretty good ballistic match for the 20mm Hispano it it more of a mismatch for most other countries guns. It's high velocity and streamline bullet means it's time of flight is going to be rather different than most other peoples 20mm guns and RCMGs.
Going with a bigger heavier projectile would mean lower MV. Eg. the Soviet 20 mm lost ~10% vs. their 12.7mm, the predecessor. For the '18 mm', it would mean going from 880 m/s down to 800 ms.
A light cannon with light enough ammo will mean a homogenous battery, ie. no pressing need to have 'back-up' machine guns. But, need be, it would come along good enough with MG 131 or MG 17 (~750 m/s).
I think it was also partially due to the MG 151 being simple to adapt to 20 mm and the 15 mm cartridge was powerful enough to allow for a reasonably high velocity for a 20 mm projectile as well. (and the 20 mm mine shell was already in production AND more effective than a 15 mm variant would be)The low 'bang-for-buck' of exploding .50 ammo is surely an issue, eg. the Germans didn't bothered much even with MG 151 and went fast to the 20 mm variant.
With the dimensions of the .50 BMG cartridge, an 18 mm projectile might manage similar or maybe higher velocity than a MG-FF or Oerlikon FF round, but likely less than the FFL, perhaps also similar to the under-loaded cartridges used on the Ho-5. (so likely in the low 700 m/s range for a 100 g projectile)Compared with Hispano II (50 kg), the weight of two '18mm' should be ~60 kg. Where 150 rds of Hispano ammo are carried, 250 rds of the 18mm might go instead (weight-wise). The MV should be lower for the proposed gun, but RoF should go to 3200 rpm for 4 of them, vs. 1200-1300 for the Hisso II. Hispano would fire a more powerful shell, 130 g vs. ~80 g.
For the Germans, the proposed gun would've been fitted more easily in the wings of the Bf 109 than a 'full power' 20 mm cannon, and contrary to the MG FF it would be belt fed. That would also allow to get rid of the cowl LMGs/HMGs.
Since the gun muzzle would be either not protruding, or just a little bit protruding, that would cut a drag a bit vs. a muzzle sticking out a foot or like.
I think it was also partially due to the MG 151 being simple to adapt to 20 mm and the 15 mm cartridge was powerful enough to allow for a reasonably high velocity for a 20 mm projectile as well. (and the 20 mm mine shell was already in production AND more effective than a 15 mm variant would be)
They did later adopt 13 mm HE or HE/I loadings, and those seemed to be more effective than the Italian attempts at 12.7 mm HE rounds. (perhaps due to the slightly larger caliber and experience with thin-walled HE shells?)
With the dimensions of the .50 BMG cartridge, an 18 mm projectile might manage similar or maybe higher velocity than a MG-FF or Oerlikon FF round, but likely less than the FFL, perhaps also similar to the under-loaded cartridges used on the Ho-5. (so likely in the low 700 m/s range for a 100 g projectile)
Adopting the 13.2 mm Hotchkiss ammunition itself might have been more attractive for many given its existing production and supply while still having somewhat higher capacity for chemical filler) Any larger calibers would mean new/unique ammunition being produced, but with the .50 BMG parent case there'd certainly be room for some attractive possibilities in the 15-18 mm range as well.
And also bear in mind that you'll be using a weapon that's significantly heavier and with heavier recoil than the Oerlikon FF -due both to the ammunition and recoil smoothing of the API blowback mechanism. (but the belt feed and potential -albeit slow- synchronization abilities would be advantageous) In fact, they'd be heavier than the FFL as well, perhaps not in recoil and likely faster firing, but heavier weapons at least.
A .70 caliber round would be just shy of the 18 mm figure (17.78 mm), but for compromise between overall ballistics and projectile size, something in the .60 cal range (15.24 mm) seems like it'd make a lot of sense. In the case of the British, aside from the idea of using a lightened browning chambered for the .5 vickers round, developing a new .60 cal heavy round based on the .50 BMG would have been interesting given it should have fairly similar ballistic performance to the .303 as well as the .50 vickers round.
(using a mix of all 3 types of ammunition for varying applications may have made sense as well and avoid the mismatch the .303 and Hispano suffered along with the difficulties in coping with the high weight, and powerful recoil of the Hispano -along with the drum feed of the early Hispano marks and Oerlikon guns)