Effect of the US produced HS.404R4M 20mm cannon being perfected pre-war?

[Shortround6]

="kool kitty89, post: 1434647, member: 12211"].. though if necking down the existing 37 mm cartridge and using the same receiver/breech/recoil mechanism, 23 mm would probably be overkill, and something in the 25-30 mm range would have gotten ballistics more in the Oerlikon S/FF S, Hispano, or .50 BMG range while having better shell capacity)[/QUOTE]

SOme of this depends on what you call ballistics. The US .50 having a shorter time of flight to a given range than the short Oerlikons,

see pg 12 for concern over manufacturing complexity of the Madsen mechanism (in particular, they cited the use of many complex curved surfaces being used, requiring complex, skilled machining operations)

It's possible that some or most of those curved parts could've been made cost-effective as stamped or possibly forged parts, but I'm not sure when that became a viable option in US industry and it doesn't seem to have occurred to anyone at the time.

How you make parts depends on how many parts you are going to make per batch and how good your foundry/fabrication techniques are at a given time.
A lot of machine gun or automatic cannon parts are subject to high stresses it takes a lot of careful work to get stamped parts to work properly, it can be done but it is actually harder than machining from solid for small batches. Same with forging, you have to make enough parts to pay for the forging dies. Tough to do with small batches of experimental guns. metallurgy in 1939-45 is nowhere near what it was in the 1960s let alone today. Forging can produce stronger, tougher parts than machining from solid but without proper technique it also might not. And very often forgings have to be finish machined to bring them into tolerance.

OTOH, if the ballistics of the 23 mm Madsen gun were considered at least acceptable, or if the US Navy had taken a greater interest in such (in spite of somewhat lower velocity), they also might have considered adapting the 20x110mm Hispano or 20x110RB cartridge of the Oerlikon Type S and FF S to 23 mm in a similar manner to the Madsen cartridge.

Good chance it won't work.

From CANNON, MACHINE GUNS AND AMMUNITION
The 20 x 120 cartridge is the Madison. The diameter of the case just in front of the rim is 29mm, for Hispano it is 24.8mm and for the Oerlikon it is 24.9mm (although I would wager you might find examples that flip those numbers.) Please note the Russian 23X115 round has a body diameter of 27mm.

The Hispano, OTOH would either have to reduce the power of its ammunition significantly to use the same mechanism, or strengthen the mechanism and add weight to cope with a more powerful cartridge. (the Madsen 20 mm cannon started out with an already somewhat more potent cartridge, so converting to 20 mm and adding a belt-feed mechanism didn't impact weight or rate of fire much)


Also, not related to US developments, but the pre-war, high power 20 mm autocannons of the IJA and Germany, both derived from anti-tank and AA guns, while rather mediocre and overweight to be efficient fighter weapons, used ammunition/cartridges that could/should have adapted well to 23-25 mm variants via simply necking them up. The MG c/30L and Ho-3 respectively firing the Swiss 20x138mmB and Japanese 20x125mm cartridges. The ground-based Flak-38 counterparts to the MG c/30L managed at least 450 RPM in later developments, so it seems reasonable that could've been maintained, and necking it out to 23 or 25 mm (possibly using Danish 23 mm or French 25 mm Madsen shell manufacturing to supplement such) should have been straightforward for producing a pretty potent early-war anti-bomber weapon, and hypothetically one that could also be synchronised and mounted in Fw 190 wing roots.

1. The Hispano often doesn't get quite the credit it deserves and
2. Some other rounds get a bit more credit.

The Hispano fired 130 gram projectiles at about 870-880 meters per second for a muzzle energy of of 50,3000 joules. when fired from the long barrel guns.
Which makes it the most powerful 20mm cartridge used in WW II in significant numbers. The larger Japanese 20 x 125 round fired an 162 gram AP projectile at 790m/s for 50,500 joules but the HE ammo was 127 grams at 820m/s and energy dropped to around 42,700 joules. The vaunted Swiss/German 20 x 138B round had a number of loadings but excluding the one used in the experimental early aircraft cannon none go over about 48,000 joules.
The Hispano had a decent rate of fire, anything that fired faster used a rather less powerful cartridge. Russian 20mm was around 36,000 joules and the MG 151 didn't go over 30,000 joules in most loadings that saw service, Japanese round used in the Ho-5 20mm army cannon also didn't go over 33,300 joules and was down loaded in later versions.

Additionally, the British, during their trials of FN Browning aircraft heavy machine guns could/should have considered those chambered for the 13.2 mm Hotchkiss gun, or the 13.2x99mm derivative (basically .50 BMG necked up to take the 13.2 mm Hotchkiss projectiles) as they were loaded to higher velocities with better armor piercing characteristics than either American or British (Kynoch Export loads were slightly heavier and hotter than pre-war American .50 loads) cartridges and on top of the high rate of fire (1050 RPM in British Trials) those guns should've been seriously considered to fit the sorts of qualities the 20 mm Hispano was being developed for, but with the advantages of being easier to adapt to existing fighters as wing or synchronized nose/fuselage mounts. (ie Gloster Gladiators could even be re-armed with them, and the high ROF of FN guns should have made synchronized mounts much more reasonable than the 500-550 RPM typical of American M2 Brownings) The 13.2 mm projectiles also should've had marginally better incendiary capacity for what that was worth at the time, though would become more important once improved incendiary and API developments were introduced.

The question I have with the FN Browning (and it may never be answered) is what was the rate of stoppages and parts breakage per 1000 or 5000 rounds fired.
It took 3 US companies over two years to get the Big Browning from 800rpm to 1200rpm at a rate of stoppages and breakage acceptable to the US Military.
Perhaps if the target goal was only 1050 rpm they could have hit it much earlier with less redesign, I don't know. Or perhaps the countries that adopted or looked at the FN Browning were more tolerant of stoppages and Breakages, I don't know that either. The early US M2 Brownings were far from trouble free once installed in aircraft, however well they may have performed on the test bench/range. One modification needed between the 600rpm and 800rpm M2 guns was to double the force the feed mechanism pulled on the belt with. The older guns slowed down with long belt attached compared to a short one. ANd that is without G forces pinning the belts to the bottom of the feed trays. The difference in internal capacity between a 12.7mm projectile and a 13.2 in minimal, you can get as big or bigger change by varying the thickness of the steel tube that forms the body holding the incendiary material. The US went a little too far with M23 incendiary with using a minimal thickness body to hold the max payload.

A lighter Browning derivative developed around the .50 Vickers cartridge should also have been possible, but would've been less ready-made and have thus required greater interest (plus further development of the Vickers .50 gun was more appealing for a time as it was initially more reliable and lighter than the .50 Browning in 1920s testing) but that cartridge had mediocre armor penetration and thus lack of interest. (I'm not sure why lighter, higher velocity AP bullet loads weren't developed, both for aircraft and AA use, as the existing ball and AP loads in the 2500-2540 fps range were rather mediocre, and while already light for .50 cal weapons at 580 grams, should still have seen similar advantages for lightening + higher velocity and higher muzzle energy on top of much better armor penetration within effective ranges ... plus a good deal of production had used flat-based projectiles, so lighter ones with better ballistic shapes could have had better all-around ballistics on top of good armor penetration, relatively light recoil, and relatively light gun weight) It's also noteworthy that the bullet shapes of .5 Vickers cartridges were already superior to those of their export derivatives used later by the Italians and Japanese and the 1920s era Vickers .5 inch aircraft gun was 24 kg compared to the 29 kg (and similar 700 RPM rate of fire) of the Breda-SAFAT heavy machine gun used by the Italians, which was perhaps the most mediocre one of the war. (the WWI vintage Vickers gun had also been prone to jams/stoppages in aircraft use, but I'm not sure how that translated to later marks or the .50 cal guns and their switch to disintegrating metal link belts, or the comparable .303 Vickers marks that had been lightened and sped up to 900 RPM that lost out to the still lighter and better performing .303 Browning, though the Japanese Army and Navy used similar 900 RPM vickers developments)

The 12.7 x 81 case was too small to take heavier, longer bullets. It may have been too small to take "trick" bullets. This depends on the gun and the max overall length of the cartridge it will handle. If your overall length is fixed than bullets with pointy noses and boat tails stick down further into the case and cut powder capacity and thus velocity. A problem well known to many experimenters trying to design cartridges for the M-16 platform.
I would note that one reason the British were able to use more pointy nose on their 12.7x81 is that they never (for good or ill) designed an exploding projectile for it and didn't need to accommodate a fuse.

Anthony Williams credits the photo to "PzGr40"

You do want all your ammo to follow similar trajectories/times of flight so designing a really streamline bullet of one type and short/fat light bullet (ping pong ball) of another type doesn't work very well.

 

[fastmongrel]

I would note that one reason the British were able to use more pointy nose on their 12.7x81 is that they never (for good or ill) designed an exploding projectile for it and didn't need to accommodate a fuse.

There were HE rounds for the 12.7 x 81 though as far as I can find out it was export only Semi Rimmed ammo never used in British service. The Italian and Japanese 12.7 x 81mm Semi Rimmed HE rounds were quite blunt nosed.