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

[claidemore]

Luftwaffe felt that it took an average of twenty hits from a 20mm cannon to down a B17/B24?
8-12 - 20mm hits on a fighter or any twin engine bomber should be more than adequate then.
Or if you are a good shot, and get 50% hit accuracy, you've just decimated your target.

 

[Ratsel]

or 5 hits for a frontal attack on a -17.

 

[Jabberwocky]

Actually I was referring to the MG151/20.

The MG151/20 AP ammunition had a mild advantage at 100 m/0 deg (24 mm vs 22 mm), but as ranges open up and angles of impact get more acute, the .50 Browning API round becomes increasingly equivalent. Beyond roughly 250 m, there is almost no difference between the AP performance of the Browning .50 API and the MG151/20 AP. At 400 m, the .50 API round becomes better at high angles of impact.

The higher initial velocity, better sectional density of the .50 round and its superior ballistic shape come into play as the range increases.

 

[davparlr]

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.

I would agree with this. The probability of two strikes of the F9F is 69% and of five strikes of the F-86 is a bit better at 75%, so, this is a good point of rough equality in fire power if the Navy is accurate in their analysis.

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!

This is interesting. It should be noted that the vibration levels of 20mm cannon fire is sufficiently big enough to require special testing of endurance for avionics equipment. I suspect that, even with center line weapons, there is a noticeable pattern spread.

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?

As already mentioned, these guns fire at a 1500 r/min rate or 6000 r/min total, or equivalent to an M61 Gatling gun. This is much more powerful than the six 50 cals previously used and twice the the rate of the F9F.

 

[zjtins]

I find much of the info to date misleading. Comparing energy of chemical (explosive) vs mechanical is pointless. The do not have the same affect on a target.

A .50 solid bullet can destroy a water cooled engine in 1 shot. A 20mm thin shelled round may explode on the engine's surface and essentially do nothing.

A .50 cal bullet can punch a .50 hole through Aluminum skin and do nothing, a 20mm thin walled shell can strip whole sheets of skin off a target aircraft when the aircraft is moving at high speed.

Many of the write ups to date are too simplistic.

There are several important categories that must be considered that a round needs to deal with, air vs water cooled engine, self sealing vs non sealed fuel tanks, small vs large aircraft (or lightweight vs robust). Also important are pilot or other armor, and round dispersion (based on distance to target and, gun positions and muzzle velocity/round drag).

In the Pacific 6x.50 cal in the wings was perfectly acceptable to shoot at non sealed fuel tanks and unarmored aircraft. Very few bullets and the plane was in flames
In the Europe 6x.50 cal in the wings also worked enough. And the P-47 damage reports with its 8 fifties were never questioned.

But 4x20mm the FW-190 and other aircraft used were also very effective. May of the Russian aircraft used 1 or 2, 20-23 mm centerline (or near to) in their fighters and found them to work on German aircraft.

Also many of the expert German pilots found the 1x 20mm center line to work well for them.

The .30 cal was universally scoffed at but in the beginning (BOB) 8 per aircraft was standard in England. They would use typically half there load to bring down 1 German but it worked.

Before a serious comparison can be made the conditions must be understood.
Shooting down a Zero vs B-17 are not the same in terms of gun needs. I have seen reports of many pilots taking down 3, 4, 5 even 7 Japanese aircraft in 1 battle. The best the Germans ever did was 2 B17's no matter what armament/airplane they used (in one battle).

When asking the question we must make sure the comparison is valid when the results are in.

 

[davebender]

A .50cal solid bullet can also accomplish very little damage when it scrapes the exhaust manifold and ricochets off into space. vs a 20mm mine shell which explodes after scraping the manifold, spraying shrapnel into ignition wires, fuel lines, hydraulic lines etc. It all comes down to luck.

Personally I wouldn't want my engine hit by either one. However you are more likely to hit the airframe then engine and explosive cannon shells are a clear winner for tearing big holes in aircraft skin.

 

[Shortround6]

WOW!!! that is some mine shell. Fuel lines on a V-12 (at least allied ones) were several feet from the exhaust manifold. You also had the cowling for your fragments to get through while retaining enough energy to cause much mischief. Mine shells were rather poor at fragmentation. Having a few exhaust stacks blown off would certainly be disconcerting and affect performance but may not cause the plane to to be lost.

The 20mm mine shell worked well in certain hit locations and was crap in other ones, just like the .50 cal bullet. They tended to work best in opposite hit locations.

 

[zjtins]

Sure but what more likely a .50 hitting mostly near center mass or a 20mm taking out lines with random shrapnel. Basically from any direction only the very outside edge of the enginee would a .50 bounce off which equates to asmall percent of the target.

Also a 20mm could not penetrate pilot armor (backseat)...it hurts but cannot penetrate the .50 could and did. Again my point is the info to date is energy based NOT terminal ballistics, target type and and round actual affect data.

But a 1 cannon ME109 was much less likely to end up with a hit than a 6 or 8 gun .50 cal US fighter when in combat. Yes they can all shoot someone down when surprise is 100% but that did not happen often.

A green pilot should have more chance of more hits with many rounds vs few rounds hence Number of guns X RPM = higher hit rate regardless for dispersion rate (can include pilot miss distance).

One reason the US went to a Gatling gun is a predictable dispersion pattern. I believe the pilot can still select a round, oval vertical or oval horizontal dispersion pattern from the gun. He does not control the random dispersion but a programmed dispersion. Greater hit probability.

 

[Shortround6]

Most people accept that a 20mm Hispano was about 3 times more effective than a .50 cal Browning. Extending this to other guns gets increasingly iffy. The .50 Browning and the 20mm Hispano had just about the same muzzle velocity and the same practical trajectory out to 700 yds or so. they had similar times of flight over practical ranges. The rate of fire was a 3:4 ratio in favor of the .50 cal.

When trying to say what a gun could or couldn't do, especially cannon, it is well to remember that many aircraft guns used mixed belts of ammunition and ammunition changed over time. Early .50s used mixed belts of tracer, AP and incendiary ammunition. The use of tracer was soon cut way back. Incendiary bullets do not penetrate as well as AP. Later the .50 got the M8 API which carried a small amount of incendiary material in front of the AP core. armor penetration was not hurt but incendiary performance per round went down will the total amount of incendiary stayed about the same and the belts standardized but this was not until 1944.

Likewise the German MG 151/20 ( different MV, shell weight, rate of fire than the Hispano) seldom used ALL one type of shell in it's belts. Most mine shells did not carry tracer, there was an AP shell or AP tracer. These could certainly penetrate anything a .50 cal could. Unfortunately for the long range shooting advocates, the mine shell was 92 grams while the none Mine HE shell, the AP shell and the tracer rounds all weighed around 117 grams and better ballistics than the mine shell, they also had a different MV than the Mine shell (mine shell higher) but they had different trajectories and different times of flight to long ranges than the mine shell.

The American Gatling gun was a very good gun but it was not magic. The dispersion could be varied but not in flight. Dispersion was changed by replacing the muzzle clamp, the bracket at the muzzles that held them in place.

 

[zjtins]

I keep seeing 3x more effective yet their seems to be no direct comparison in field data. Also in theory an 8 gun P-47 if loaded with 4 guns x 20 mm and be 8/4*3 = 6 times more effective. Yet you look a the 4x20mmm FW-190 results and I don't see this any remarkable difference in there results there are about even in the field performance (in terms of gunnery and target destruction).

 

[Shortround6]

You just fell into the comparing apples and oranges trap.

The US Navy figured the 20mm Hispano was 3 times more effective than the . 50 Browning.

Comparing to the MG 151 throws in a whole bunch of new variables.

The MG 151 had a lower MV and a worse ballistic coefficient than the .50 which means longer flight times and more deflection needed. Rate of fire was better than the Hispano but not quite as good as the .50 so the .50 is easier to hit with.
The .50 was closer in power to the MG 151/20 and AP capability was close. The 20mm mine shell wins the "bang" contest with ease but not every round in the belt was a mine shell. MG 151 did more damage but was harder to hit with.

BTW the math is a bit off. 4 20mm Hispanos equal 12 .50cal Browning's. Twice as effective as six .50s but only 1.5 times eight .50s.

 

[zjtins]

My bad should be 4/8*3 =1.5.... good catch. See raw analysis does not always work.

The MG 151 had a lower MV and a worse ballistic coefficient than the .50 which means longer flight times and more deflection needed. Rate of fire was better than the Hispano but not quite as good as the .50 so the .50 is easier to hit with.

Now your are proving my point. 6 to 8 .50 cal worked, there was not an overwhelming need to change, unlike 8 x .303.

 

[Shortround6]

Now your are proving my point. 6 to 8 .50 cal worked, there was not an overwhelming need to change, unlike 8 x .303.

Overwhelming need? Not against the targets they usually faced but the US Navy stopped ordering planes with .50cal machine guns in the winter of 1944/45. They took delivery of previous orders for quite some time. The need for CAP to DESTROY Kamikaze aircraft (not just shoot them down, there is a difference) had the navy scrambling for effective fire power. A number of Corsair radar equipped night fighters changed their .50 cal guns for 20mm guns.

 

[zjtins]

Again no overwhelming need. The 20 mm of the day in the US was terrible. I dont believe the Navy accepted for full production a 20mm single barrel until the Crusader jet. They were constantly tweeking it to make It work right.

US Navy stopped ordering planes with .50cal machine guns in the winter of 1944/45. They took delivery of previous orders for quite some time...

Seriously? then how come the overwhelming majority of US aircraft used in Korea were .50 armed?

 

[Shortround6]

Why don't you look it up?

There was a difference between the US Navy and the US Air Force.

Navy jets fighters (only) that used 20mm cannon BEFORE the Crusader.

Chance Vought F6U-1 Pirate.
McDonnell F2H Banshee
Grumman F9F Panther
North American FJ-2 and up Furies.
Douglas F3D Skyknight
Chance Vought F7U Cutlass
The Douglas F4D Skyray
McDonnell F3H Demon
Grumman F9F Cougar
Convair F2Y Sea Dart
Grumman F9F Tiger

10 fighter designs BEFORE the Crusader. Why don't you count up the post war piston engine planes, both fighters and attack aircraft and add in the Navy jet attack and bombers armed with 20mm guns before the Crusader ever flew?

 

[zjtins]

From Britain, Switzerland and USA 20 mm/70 (0.79") Oerlikon Marks 1, 2, 3 and 4

In 1944-45, the USN found that 20 mm shells were too light to stop Japanese Kamikaze planes and the higher approach speeds of these planes made manually controlled guns obsolete. As a result, Oerlikons were replaced by 40 mm Bofors where ever possible during 1944-45 and removed entirely from most US ships by the mid-1950s.

And the only successful plane was the F9F panther. And as I said the 20mm had problems until the Colt (number?) version of the 20mm, finally, on the Crusader the earlier versions were considered problematic.

10 fighter designs BEFORE the Crusader. Why don't you count up the post war piston engine planes, both fighters and attack aircraft and add in the Navy jet attack and bombers armed with 20mm guns before the Crusader ever flew?

Irrelevant, they were not considered successful or built in numbers. Even the Panther only shot down a few Migs.

The most numerous and successful US fighter on Korea was the F-86 Sabre, most with 6x .50 cal. The wish to move to move on the Sabre to 20mm was mainly for range not firepower.

 

[zjtins]

Also around 1400 Panthers were built vs around 7,000 F-86.
The rest you quote were small numbers (200-400) and rarely used in CAP usually relegated to ground.

 

[Glider]

The most numerous and successful US fighter on Korea was the F-86 Sabre, most with 6x .50 cal. The wish to move to move on the Sabre to 20mm was mainly for range not firepower.

Its rrobably more accurate to say that the change from 6 x 0.5 to 4 x 20mm was to improve effectiveness not just range or firepower but a combination of both. Either way, the important thing was that the change to 20mm was the way forward.

Across the free world it might be instructive to think about the number of designs that had the 0.5 and those that had the 20mm. All the designers had a free choice as to what to arm their aircraft with and the majority, the vast majority went away from the 0.5.

 

[Shortround6]

" I dont believe the Navy accepted for full production a 20mm single barrel until the Crusader jet"

The statement was wrong and very, very far from the truth wasn't it.

"The rest you quote were small numbers (200-400) and rarely used in CAP usually relegated to ground."

Chance Vought F6U-1 Pirate. 33 built
McDonnell F2H Banshee. 895 built.
Grumman F9F Panther. 1382 built.
North American FJ-2 and up Furies. 741 -2 -3 Furies---374 -4 Furies= 1115 total.
Douglas F3D Skyknight. 265 built
Chance Vought F7U Cutlass. 320 built.
The Douglas F4D Skyray. 422 built.
McDonnell F3H Demon. 519 built.
Grumman F9F Cougar. 1392 built.
Convair F2Y Sea Dart. 5 built.
Grumman F9F Tiger. actually the F11 Tiger 200 built.

Well you were right 50% of the time. Still don't see a single .50 cal armed plane in the bunch though.

For Piston engine fighters.

297 F4U-4Bs or F4U-4Cs with four 20mm cannon.
223 F4U-5s, 214 F4U-5Ns, and 30 F4U-5P reconnaissance models, all with 20mm cannon.
111 AU-1 ground attack Corsairs with 20mm guns.
605 (?) F8F Bearcats with 20mm guns
364 F7F Tigercats with mixed armament 4 .50s and 4 20mm but when guns had to go to fit radar it was the .50s that went.

Now at about 4 guns per plane that is a heck of a lot of 20mm guns (not including spares) for the Navy not to have "accepted for full production a 20mm single barrel"

The just under 700 F8F-1 Bearcats armed with .50 cal guns were on order before the winter of 1944/45.

What the Air Force was doing is irrelevant to what the Navy was doing.

"The wish to move to move on the Sabre to 20mm was mainly for range not firepower"

Have you got a source for that?

 

[tyrodtom]

Shouldn't the 3000+ Skyraiders be in that total also, all with 4- 20mm.