50 cal (high rate of fire) vs 20mm cannon (hitting power)

[Greyman]

Thanks for that. I suppose one factor was that aircraft guns tended to be tuned to give the highest performance for the least weight, and were often operating on the ragged edge of reliability. The Soviets, for instance, worked out that the life of an aircraft gun in combat was very short, so they built them to last only just long enough.

From the Air Historical Branch re: Hispano V --

It was decided to take this opportunity to redesign the gun completely and to incorporate into the new gun; the short barrel, increased rate of fire and light weight. One of the first questions to decide was the acceptable life of the new gun. Before the war a life of at least 20,000 rounds was expected for rifle calibre guns, and the acceptable life of the Hispano 20-mm gun had been fixed at 10,000 rounds. It was apparent that under active service conditions few aircraft survived to give 10,000 rounds and an investigation was made to determine the actual life of guns under war service. The results were surprising: it appeared that very few guns ever reached 1,000 rounds, and the majority only fired a few hundred before the aircraft crashed or was lost in action. There was obviously no point in aiming at a 10,000 rounds life, and the Air Staff were asked to accept one of 1,500 rounds. ​

​

... ​

​

Subsequent experience with production guns in service showed that the average life of the smaller components was 2,500 to 3,000 rounds, while the barrel was good for at least 5,000 rounds. ​

 

[A.G. Williams]

The Oz made 20mm ammo was terrible, a new factory was set up at St Mary's on the outskirts of Sydney and it was way out of spec.

Right, thanks.

 

[A.G. Williams]

Do we have some quantification about the number of bullets fired before the guns were rendered useless? Eg. when Soviets tested the Beresins' HMG, the guns were good for 10000-12000 rounds fired.

I have a few bits and pieces of information concerning Soviet aircraft guns.

The NS-23 (right at the end of WW2) lasted for 4,000 rounds free, or 3,000 synchronised (more little pieces to go wrong)
The AM-23 (1950s) managed 6,000 rounds
The NR-30 (1950s) 2,000 rounds initially, later 3,000 rounds
The R-23 (1960s) 3,000 rounds
The GSh-23 (1960s) 4,000 rounds (after modification to enhance life)
The GSh-30 (1970s) 4,000 rounds
The GSh-301 (current gun in Su-27 and MiG-29 families): 2,000 rounds (1,000 rounds for the barrel).

For comparison, the US M61A1: gun life 90,000 rounds, barrels 15,000, certain other parts 30,000.

 

[Clayton Magnet]

The GSh-301 (current gun in Su-27 and MiG-29 families): 2,000 rounds (1,000 rounds for the barrel).

For comparison, the US M61A1: gun life 90,000 rounds, barrels 15,000, certain other parts 30,000.

The GSh-30-1 is also remarkably light and compact, with a fantastic rate of fire for a 30mm non-revolving cannon

I would be curious to see any information regarding the reliability of the 20mm cannon version of the Beresin. The B20 checks a lot of boxes for a fighter weapon, light weight and hard hitting

 

[tomo pauk]

I have a few bits and pieces of information concerning Soviet aircraft guns.

The NS-23 (right at the end of WW2) lasted for 4,000 rounds free, or 3,000 synchronised (more little pieces to go wrong)
The AM-23 (1950s) managed 6,000 rounds
The NR-30 (1950s) 2,000 rounds initially, later 3,000 rounds
The R-23 (1960s) 3,000 rounds
The GSh-23 (1960s) 4,000 rounds (after modification to enhance life)
The GSh-30 (1970s) 4,000 rounds
The GSh-301 (current gun in Su-27 and MiG-29 families): 2,000 rounds (1,000 rounds for the barrel).

For comparison, the US M61A1: gun life 90,000 rounds, barrels 15,000, certain other parts 30,000.

Thank you.
Do you have anything on the ww2 era guns.

 

[A.G. Williams]

Thank you.
Do you have anything on the ww2 era guns.

Sorry, I don't.

 

[A.G. Williams]

The GSh-30-1 is also remarkably light and compact, with a fantastic rate of fire for a 30mm non-revolving cannon

Yes, it is an outstanding design. It fires ammo with the same power as the 30mm MK 103, but at four times the RoF while weighing only one-third (about the same as an MG 151/20) - in other words, it is 12x better in hitting power per kg. PS: it looks as if it could fit in a Bf 109 engine mounting - that would have changed the terms of air warfare!

I would be curious to see any information regarding the reliability of the 20mm cannon version of the Beresin. The B20 checks a lot of boxes for a fighter weapon, light weight and hard hitting

The Beresin was another outstanding design, matching the performance of the ShVAK at little more than half the weight and was also more compact, yet was stated to be "more reliable". It is a mystery why this was not adopted much earlier than October 1944 as the adaptation to fire 20mm rather than 12.7mm ammo was quite straightforward.

 

[OldParts]

Williams' books are excellent or go to his excellent online resource which he linked above. As others have pointed out not all weapons of the same caliber (diameter) are the same. An example that is familiar to most folks is the 38 special and the 357 magnum. They have the same bore and you can fire 38s in a 357 but you can fire a 357 in a 38 because the cartridge of the 357 is longer. According to the late Jeff Cooper, the case of the 357 was lengthened to prevent people firing the 357 MAGNUM in a 38 which was not built to stand the increased chamber pressure. I once fired about 100 rounds of 38 and 100 rounds of 357 through a light weight (J frame) 3 inch S&W. The 38 and the 357 are the same caliber but the muzzle velocity of the 357 is probably about 40 percent higher than the 38 (depends on the brand, bullet weight, and barrel length). The pistol had stock wooden grips and the web of my hand was bleeding after firing the 357 rounds. Until reading Williams, I had no idea of how large the differences were in the same caliber of automatic cannon and HMG ammunition. Another factor is the type of projectile used (ball (solid), HE, or incendiary, or HEI. What the Browning 50 had going for it was high reliability and projectile that was not so dependent upon an explosion to do a lot of damage. The HS 20 also used a heavy projectile. But many of the German (and Japanese) cannon used thin skinned shells with low muzzle velocities.

 

[strider190]

If you were a fighter pilot in WWII, would you rather have the high rate of fire of the 50 cal, or the hitting power of the 20mm? I personally feel the 50 cal was plenty hard hitting enough to take out ANY aircraft, and its high rate of fire made it even more effective...the slow rate of fire for the 20mm meant you had to be a much better marksman...

 

[strider190]

If you were a fighter pilot in WWII, would you rather have the high rate of fire of the 50 cal, or the hitting power of the 20mm? I personally feel the 50 cal was plenty hard hitting enough to take out ANY aircraft, and its high rate of fire made it even more effective...the slow rate of fire for the 20mm meant you had to be a much better marksman...

I'd take a 20mm over a .50 cal anytime. Most WW2 fighter types would have agreed. Explosive! No contest.

 

[Timppa]

The Beresin was another outstanding design, matching the performance of the ShVAK at little more than half the weight and was also more compact, yet was stated to be "more reliable". It is a mystery why this was not adopted much earlier than October 1944 as the adaptation to fire 20mm rather than 12.7mm ammo was quite straightforward.

I quote Milos Vestsik's book ("Lavockin La-7"):
"The reliability of the cannon was also never to reach the required level, this is documented by the tests carried out with La-7 aircraft, at the NII VVS from September 10 to October 1945. Of the three aircraft in test, none were to attain the expected service life of 5,000 rounds fired (the first test fired 3,275 times, the second 3,222 times, the third 3,155 times)."

 

[A.G. Williams]

I quote Milos Vestsik's book ("Lavockin La-7"):
"The reliability of the cannon was also never to reach the required level, this is documented by the tests carried out with La-7 aircraft, at the NII VVS from September 10 to October 1945. Of the three aircraft in test, none were to attain the expected service life of 5,000 rounds fired (the first test fired 3,275 times, the second 3,222 times, the third 3,155 times)."

Well, my source only said that the Beresin was "more reliable" than the ShVAK.

I think that the La-7 tests showed astonishing consistency, and the results were almost certainly good enough for combat purposes.

 

[Schweik]

This may help. From USAAF microfilm report.

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Wow that is one hell of a cool post right there...

 

[jmcalli2]

This may help. From USAAF microfilm report.

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Some interesting comparisons here:

The WWII Fighter Gun Debate: The Fighters

 

[Thumpalumpacus]

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Yes the Hispano's were big.
Hispano's were a hybrid gun. They used a combination of gas and recoil. The shorter lighter barrel helped with the increase in the rate of fire.

Must be a Californian, he's texting even on the flight line.

 

[Koopernic]

I have a few bits and pieces of information concerning Soviet aircraft guns.

The NS-23 (right at the end of WW2) lasted for 4,000 rounds free, or 3,000 synchronised (more little pieces to go wrong)
The AM-23 (1950s) managed 6,000 rounds
The NR-30 (1950s) 2,000 rounds initially, later 3,000 rounds
The R-23 (1960s) 3,000 rounds
The GSh-23 (1960s) 4,000 rounds (after modification to enhance life)
The GSh-30 (1970s) 4,000 rounds
The GSh-301 (current gun in Su-27 and MiG-29 families): 2,000 rounds (1,000 rounds for the barrel).

For comparison, the US M61A1: gun life 90,000 rounds, barrels 15,000, certain other parts 30,000.

What kind of stoppage rates and barrel life do modern guns achieve?

 

[Greyman]

I can't find the document anywhere at the moment, but I have an RAF report on fighter operations in Tunisia (I think) that noted the importance of weapon maintenance in this regard, giving figures for the average Hispano stoppage rate and the rate of the worst squadron in this respect. The difference was significant.

Found it (report from an Ordnance Board Mission to North Africa and Malta).

20 m.m. Hispano Gun Mks. I and II and U.S. M2.
The performance of this gun is generally satisfactory, but it is stressed that this is only after personnel have become thoroughly versed in the meticulous maintenance necessary under active service condition ... the stoppage rate varies from one in 350 rounds to one in 2000 rounds in different squadrons.

 

[A.G. Williams]

Found it (report from an Ordnance Board Mission to North Africa and Malta).

20 m.m. Hispano Gun Mks. I and II and U.S. M2.
The performance of this gun is generally satisfactory, but it is stressed that this is only after personnel have become thoroughly versed in the meticulous maintenance necessary under active service condition ... the stoppage rate varies from one in 350 rounds to one in 2000 rounds in different squadrons.

US figures I have seen (France, 1944) show one stoppage for every 1,500 rounds with the Hispano, one for every 4,500 rounds for the .50 M2.

 

[MIflyer]

Well, remember that the .50 had Armor Piercing Incendiary ammo by 1944 and that really improved its already impressive lethality. Reports from the Pacific reveal that Hellcats were shooting down Vals and such with one carefully aimed round.

And when the RAF realized they would have no choice but to use Spitfires as fighter bombers after the invasion of Normandy they pushed to remove the four .303 guns and replace them with twin .50 cal as soon as possible.

 

[Shortround6]

Please remember that there are 3 different metrics here, at least.

Stoppages per XXX number of rounds, this can be a simple jam, round got a bit cross wise, or it can be a broken part. might be a dud round but those might be filtered out (or not, depending on source or country)

Broken parts were sometimes listed separately. as in broken parts per XXXX rounds fired. Broken part will usually result in a stoppage.

The you have barrel life and gun life.
Barrel life is how many rounds you can fire through a barrel before enough rifling gets worn/burned away to affect accuracy and velocity to a certain limit. Perhaps also a variable between nations?
Gun life is when major components, like receiver and bolt are so worn than it is no longer worthwhile to put in new parts or installing new parts (like a new bolt) will not bring the gun back to factory tolerances.

The Browning M2 and the Hispano could often be rebuilt/overhauled several times before the receiver was stretched/worn enough that installing new parts would fail to bring it back to operational status.