20mm cannon, best, worst, specs, comparison to LMG, HMG etc.

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bailing out during the late war especially. heres a direct quote from a friend of mine:

' I had to resist the urge to pull the ripcord to early. This would be very dangerous: far too many comrades have been machine-gunned while hanging in their chutes recently. '
 
Jabberwocky said:
110 g seems VERY light. Which 20 x 110 round would that be? Have you got a designation number?
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The only source I could find quickly is this one showing 20mmx110(USN) data. This relates to the 1950s.

ANTI-TANK AND HEAVY MACHINE GUN CARTRIDGES UP TO 19 MM CALIBRE

And a reference to a lighter projectile in Wikepedia site
Hispano-Suiza HS.404 - Wikipedia, the free encyclopedia

stating:

while the Navy instead combined the original Hispano design with a lighter round for better muzzle velocity in the Colt Mk 12 cannon
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The British had a a MK 5.z round with a 113gm projectile but the main (Only?) reason for the lighter weight was that the fuse was made of aluminium instead of brass. American 20mm ammo for the M-39 and Vulcan guns used 102 gram projectiles.

The round used in the Colt MK 12 used a lighter projectile but also used a fatter cartridge case with a bigger propelling charge. This can be seen in the photograph areas of Tony William's web site which Davparlr has so kindly linked to.
 

Ah, I see where the confusion is arising.

The 20 x 110 USN is ANOTHER 20 mm cartridge, distinct from the Hispano and the Oerlikon.

The cartridge was used in the Colt Mk 11 and Mk 12 - which were derivatives of the Hispano used in the 1950s. The case had a larger capacity than the 20 x 110 Hispano and the round was indeed 110 g. The Mk 12 fired at around 1000 rpm and about 1000 m/sec - something of an improvement over the 750 rpm and 800 m/sec of the Hispano Mk V/M3

The Wiki link says "The Hispano fired a 130 g (4.586 oz) 20 mm diameter projectile" - but its quoting Emmanuel Gustin, who I referred to earlier.
 

Okay, now I see I was also confused. The F9F uses the M2 cannon (according to Wiki) so I assumed it used the Navy 20x110(USN) round, which, in reality, probably didn't appear until the mid 50s, and the AF used the standard 20x110 round. This was probably wrong. In this case, the weight would be 130g. I will recalculate throw weight. It does not negate my probability analysis results however, since it was base on r/sec and Navy analysis of a 1 to 3 difference in effectiveness of the 20 over the .50, and not throw weight.
 
Ratsel said:
M61 trumps them all. more then enough to knock down the starship Enterprise.
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Anti-matter projectiles from the M61 don't have enough velocity to penetrate her shields. It would only work if you could hit her with her shields down. I have a US airforce study on that subject from 1969 laying around here somewhere......
 
The M61 isn't the compleletly perfect system . It takes it almost a second to accelerate the barrels up to the full firing rate, in the first 1/2 second it only fires 18 rounds. In modern aerial combat, you're lucky if you can stay on target a second. There are different installations, but for example the F/A 18 only carries 570 rounds.
 
pinsog said:
Anti-matter projectiles from the M61 don't have enough velocity to penetrate her shields. It would only work if you could hit her with her shields down. I have a US airforce study on that subject from 1969 laying around here somewhere......
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We are the Borg. We have assimulated the M61. Your shields are useless. Surrender your ship. We will add your biological and technological distinctiveness to our own. Your culture will adapt to service us. Resistance is futile. 12/21/2012.
 
Ratsel said:
We are the Borg. We have assimulated the M61. Your shields are useless. Surrender your ship. We will add your biological and technological distinctiveness to our own. Your culture will adapt to service us. Resistance is futile. 12/21/2012.
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Mr. Data, lock .50's on the Borg cube. A single short burst should destroy it.
 
davparir: to be more precise, at 5% the F9F would be 2 hits x 3 damage for a factor of 6, while the F86 would be 5 hits x 1 damage for a factor of 5, which is an advantage to the F9F. At 10% it would be 6 for the F9F, 7 for the F86. They should be equal somewhere between those two percentages.

It's interesting that one of the arguments for mgs vs cannons is that the mgs have higher rate of fire and give a 'pattern' which should increase the probability of a hit, particularly from a less skilled pilot.....yet it has been many many times argued that the centerline armament configuration is superior to wing gun configuration because the 'pattern' of the wing guns is held to be less lethal!

With the F86H they finally went to the M39 20mm cannon. Question is, did they switch to the cannon because they now had effective radar sights which took away the advantage of the 'pattern' from the .50s and ensured shot placement from the slowwwwwer firing 20mms? Or did the radar sights eliminate that last excuse for hanging on to the much loved.50s?
 

M39 wasn't slower firing than the M3 Browning, it was faster.

M39 fired at around 1500 rpm, +/- about 25 rpm. MV was in the order of 1000-1050 m/sec.

M3 fired at about 1200 rpm, +/- about 50 rpm. MV was about 880 m/sec.

Disadvantage is that the M39 weighs more than twice what the M3 does.

They did go with a slightly less powerful cartridge, in the form of the 20 x 102 round, which weighed about 100 grams - around 10% less than the Navy's 20 x 110 and about 30% less than the original Hispano round.
 
"Slowwwwer" firing 20mm was a tounge in cheek reference to the Hispanos and other available non-revolving cannons that were passed over for the six gun .50 armament. I guess I should have said slowwwwer firing Hispano.
I did some checking and the F86H carried 600 rds, or enough for 6 seconds of firing time.
Again, was the radar sight the deciding factor in switching to 20mm, or was the switch made on the merits of the 20mm itself?
If the radar sight makes hit probability almost a guarantee, then why not stick to the .50s?

One reason to swicth to 20mm, http://www.ww2aircraft.net/forum/aviation/armor-penetration-20mm-vs-50-cal-911.html In post #3 check out the difference in armor penetration when not at 0 degrees angle
 
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I said before that the speed issue was a non-issue. the 20mm has the most penetrating power, whether at 0 or 45 degrees.
 
Ratsel said:
I said before that the speed issue was a non-issue. the 20mm has the most penetrating power, whether at 0 or 45 degrees.
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It depends on the ammunition that each weapon is firing.

Hispano 20 mm AP Mk II will outperform Browning 12.7 mm AP and AP-I - 27 mm vs 20 mm at 200 yards, 24 mm vs 14 mm at 400 yards. Performance difference increases as the angles of impact become more oblique.

Hispano 20 mm SAP-I has about identical penetration as 12.7 mm AP-I at 200 yards. Again the 20 mm's penetration advantage increasing as the range opens and angles of impact become more oblique.

However...

12.7 AP-I and ball rounds comfortably out-penetrate 20 mm ball and 20 mm HE-I at all ranges and angles. This is important, as AP-I dominated M2 belting, while Hispano belting was predominately HE/HE-I and Ball in 1941/1942 and then increasing amounts of SAP-I/HE-I from 1942 onwards.

The use of pure AP in the Hispano was comparatively rare, although some Typhoon units were known to use AP heavy belting in 1944 on ground attack operations. Only about 2% of Hispano ammunition produced during the war was pure AP. Some specialised Hispano AP ammunition had more than 65 mm of penetration - enough to penetrate the side armour of most tanks during the war!
 
Actually I was referring to the MG151/20. Sorry I should have been more clear. I was never a fan of the Hispano.
 
How can you not be a fan of the Hispano? The Hispano MkII fired a 20% heavier projectile at 2887 fps, 500 fps faster than the MG151/20. It was basically the 'magnum' of the 20mm cannons during WWII. The only cannon that fired a more powerful round was the Rheinmetall*Borsig MG C/30L, but it was too slow firing to get high hit probability in air to air fighting.
The only advantage the MG151/20 had over the Hispano was it's lighter weight and higher cyclic rate of 750 compared to 600 for the Mk II Hispano. This was adressed with the Mk V, which gave the Hispano the same weight, same cyclic rate, but maintained the heavier projectiles and faster muzzle velocity.

I consider the 151/20 to be an excellent cannon, but the Hispano has distinct advantages which I believe make it a better one.
 
well I dunno. there all the same really. AP rounds for say an IL-2 HE for anything else. can't see AP rounds being used on a -17 or a -51, no need. HE gets the job done. Especially on fuel systems/electrical/etc. BUT in a dogfight, your not gonna wait to fire at the engine/fuel tank/whatever, e/a comes to bear, you pull the trigger and hope for hits. AP is fine HE is better in this situation. both can penetrate 4mm of steel. the Mg151/20 HE shell packs a very powerful punch. more so then the Hispano.

cheers.
 

Point taken, but having 20mm guns doesn't make the shooter more accurate.
Out of a 2 second burst of (8)50 cal, you'd have a 25 percent hit accuracy for 200 rounds of bullets if your shot landed for half a second out of that burst for a total of 50 bullets in a concentrated area.
With a pair of 20mm, you might land 8-12 rounds with a certain sum only being HE rounds if dealing with in the same margins.
I guess its important to consider the installation as it is important to consider ammo type.
 
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