USAAF 0.60-caliber Machine Gun????

one13 said:
Avimimus said:
Quick question: Wasn't there a P-38 that was trialled (or at least mocked-up) with 0.60cal guns?
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Hi,
there was a prototype tested with three .60 inch guns, the barrels extended quite a way foward of the nose. It did not work very well, I think they had problems with the feed systems.
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Really? I would've thought Chinn would have mentioned that considered he mentioned the tests of the design on the XP-83.
 
The P-38 tests were done in 1947, according to the Schiffer book (whose title I don't recall just now). There were multiple gun failures.

All of the 0.60-cal guns had reliability problems, and none were ever fully developed. I've always wondered what possessed the USAAC and Ordnance Department to pursue a line of development that everyone else abandoned in favor of 20-mm shell-firing cannon. This seems especially odd since the 0.60-cal guns were developed from the 20-mm Hispano and MG151/20, the latter a more effective, 20-mm conversion of a 15-mm (~0.60-in) machine gun.
 
In a way, two of the .60 cal guns were fully developed: what became the M39 revolver cannon and the M61 rotary were initially developed in .60 cal, but then modified before adoption by necking out the cartridge to 20mm - just as Germany did with the MG 151/20. The resulting 20 x 102 round is still very much in service.
 
Isn't the smaller of two popular post-war Soviet 23mm calibers itself a necked up version of the 14.5mm cartridge used in the KPV (and earlier WWII AT rifles)? Seems like a pretty common practice.
 
Cannonfodder43 said:
Colonial-Marine said:
Isn't the smaller of two popular post-war Soviet 23mm calibers itself a necked up version of the 14.5mm cartridge used in the KPV (and earlier WWII AT rifles)? Seems like a pretty common practice.
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Yes, the 23x115mm is just a necked up 14.5mm.
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It may be worth pointing out that while most necked-up cartridges retain the same overall length (thereby requiring only a barrel swap to change the ammo) the 23 x 115 has a long projectile which means that the guns for it need a longer action and body compared with the 14.5mm. The Russians have been toying with a suitably lengthened KPV to take the longer 23mm ammo, known (last I heard) as the KPVB.
 
Hi iverson,

iverson said:
The P-38 tests were done in 1947, according to the Schiffer book (whose title I don't recall just now). There were multiple gun failures.
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Additionally, in "Fighter Pilot's Heaven" by Donald S. Lopez, tests of the 0.60" machine gun in a P-38 during WW2 is mentioned (p. 15f). Lopez did the functional firing tests under steady accelerations up to 6 G, during which the gun worked reliably, but he noticed considerably barrel vibration during firing. It turned out that the original design of the gun mounts was not suitable for the guns, and as far as Lopez states that basically killed the hopes of getting the 0.60" gun into service during the war.

Lopez also did night firing trials, and found that the muzzle flame was massive, blinding him seriously (though he was advised to keep one eye closed when pulling the trigger, which turned out to be quite vital), and he reports circling for 15 minutes after firing off the ammunition while waiting for his night vision to return so he could return to base and land.

Regards,

Henning (HoHun)
 
HoHun said:
Hi iverson,

iverson said:
The P-38 tests were done in 1947, according to the Schiffer book (whose title I don't recall just now). There were multiple gun failures.
Click to expand...

Additionally, in "Fighter Pilot's Heaven" by Donald S. Lopez, tests of the 0.60" machine gun in a P-38 during WW2 is mentioned (p. 15f). Lopez did the functional firing tests under steady accelerations up to 6 G, during which the gun worked reliably, but he noticed considerably barrel vibration during firing. It turned out that the original design of the gun mounts was not suitable for the guns, and as far as Lopez states that basically killed the hopes of getting the 0.60" gun into service during the war.

Lopez also did night firing trials, and found that the muzzle flame was massive, blinding him seriously (though he was advised to keep one eye closed when pulling the trigger, which turned out to be quite vital), and he reports circling for 15 minutes after firing off the ammunition while waiting for his night vision to return so he could return to base and land.

Regards,

Henning (HoHun)
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Hi Henning,

Do these reports say anything about which .60 cal MG was involved? Modified versions of both the MG 151 and the Hispano were made for this ammo in the US.

The size of the muzzle flash is connected to the barrel length. If the barrel is too short for the cartridge, then you will get a large muzzle flash as the propellant continues burning after leaving the muzzle.
 
Hi Tony,

Tony Williams said:
Do these reports say anything about which .60 cal MG was involved? Modified versions of both the MG 151 and the Hispano were made for this ammo in the US.

The size of the muzzle flash is connected to the barrel length. If the barrel is too short for the cartridge, then you will get a large muzzle flash as the propellant continues burning after leaving the muzzle.
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Unfortunately, he doesn't state the gun type. He mentions that he was quite impressed by the barrel length though, as the barrels stuck out 3 feet from the nose of the P-38 (two 0.60" guns were installed), though.

I thought he stated that the rest of the nose was used to install camera and other recording equipment, but re-reading the pages, it looks like I confused that with comments he made later in the book about testing the Davies Draper sight.

The project officer in charge of the tests was Colonel Moon of Wright field, just in case it helps you to place the weapon from the context.

Regards,

Henning (HoHun)
 
one13 said:
Avimimus said:
Quick question: Wasn't there a P-38 that was trialled (or at least mocked-up) with 0.60cal guns?
Click to expand...
Hi,
there was a prototype tested with three .60 inch guns, the barrels extended quite a way foward of the nose. It did not work very well, I think they had problems with the feed systems.
Click to expand...
I'm not sure if this helps, but the P-38 in this picture appears to be BUNO 44-23801, not sure if the book the image it is from states that but this seems to be the best match I could find...
 
Rickshaw said:
CuteTransAngel said:
Rickshaw said:

sorry, no idea.
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Ah darn, I'll update if you if I can figure it out myself, looks like I've got a long night/morning digging through old radar systems lol
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Thanks, that should prove interesting.
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The shape and mounting of the Radar look identical to the Radar mounted on the 75 MM M 51 skysweeper towed AAA gun fielded by the US during the 1950s. If so it would be an AN/GPG 1(XF-2), at least this is what the data plate reads on an early model.
 
This is what R.P. Hunnicutt says on the T100 in Sheridan. A History of the American Light Tank:

Near the end of World War II, the .60 caliber machine gun was under development as an aircraft weapon. On 24 June 1948, OCM 32262 initiated a project to use this machine gun in a multiple mount as a short range antiaircraft weapon. Radar controlled, it mounted four T17E5 .60 caliber machine guns and was nicknamed Stinger. The T41 light tank was selected as the most suitable chassis to provide a self-propelled mount for the Stinger. A meeting was held at Detroit Arsenal to determine the necessary modifications to the T41 light tank chassis to meet the requirements of the Stinger installation. On 16 March 1950, OCM 33209 designated the new vehicle as the multiple caliber .60 machine gun motor carriage T100. Since it was the most readily available, the chassis from one of the M37 light tank pilots was reworked at Detroit Arsenal for use as the pilot T100. This chassis was shipped to the Sperry Gyroscope Company, Great Neck, Long Island, New York on 17 September 1951 for the installation of the turret and firecontrol system.

Combat loaded with its crew of three, the T100 weighed about 22 tons. The unarmored turret with the four .60 caliber machine guns rotated 360 degrees and the elevation ranged from -10 to +90 degrees. A total of 4000 rounds of ammunition were provided for the .60 caliber machine guns.

Unfortunately, the .60 caliber machine gun itself was a major problem. It had numerous failures during the development program and did not provide reliable performance. Interest also was shifting toward the use of heavier caliber antiaircraft weapons and as a result, the T100 program was terminated.
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The only two known photos of the T100 come from this book.
 

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iverson said:
The P-38 tests were done in 1947, according to the Schiffer book (whose title I don't recall just now). There were multiple gun failures.

All of the 0.60-cal guns had reliability problems, and none were ever fully developed. I've always wondered what possessed the USAAC and Ordnance Department to pursue a line of development that everyone else abandoned in favor of 20-mm shell-firing cannon. This seems especially odd since the 0.60-cal guns were developed from the 20-mm Hispano and MG151/20, the latter a more effective, 20-mm conversion of a 15-mm (~0.60-in) machine gun.
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As near I can figure out, the USAAC/F wanted a very high velocity gun, probably to make aiming and leading easier. Based on the Anzio Ironworks 20/.50 published data, you'd be looking at a ~900grain projectile at roughly 3600fps. The 20/.50 is the standard 20x102mm casing necked down to .50cal.

Related to that, I think the USAAF had missed an important lesson from Europe about what it takes to stop a bomber. But the USAAF was always flying escort missions to try to stop the Luftwaffe interceptors, so it kinda follows.

The USN got the lesson from having to try to stop kamikaze attacks, almost all their late war fighter variants had 4x 20mm instead of 6x .50cal.
 
Kamikaze resulted in a different lesson for the USN. With them, the Navy saw them more as anti-ship missiles and found that you had to physically destroy one to stop it. It wasn't sufficient to damage one, particularly when already terminal, to stop it from hitting the target.
The result of that was the 20mm on ships were being removed in favor of more 40mm as an immediate improvement, but the real solution at the time was to go to the 3"/50 twin automatic mount and introduce a surface-to-air missile.

Killing bombers for the USAAF by late WW 2 was slowly progressing in the same direction with development of an air-to-air missile as well.
 
T. A. Gardner said:
Kamikaze resulted in a different lesson for the USN. With them, the Navy saw them more as anti-ship missiles and found that you had to physically destroy one to stop it. It wasn't sufficient to damage one, particularly when already terminal, to stop it from hitting the target.
The result of that was the 20mm on ships were being removed in favor of more 40mm as an immediate improvement, but the real solution at the time was to go to the 3"/50 twin automatic mount and introduce a surface-to-air missile.

Killing bombers for the USAAF by late WW 2 was slowly progressing in the same direction with development of an air-to-air missile as well.
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Stopping a terminal kamikaze is not where the USN fighters should be, however. The fighters should be well outside the AA gunnery range, before the kamikazes get into their terminal attacks. And that's where you can get away with 20mm cannons.
 
Hi Scott,

Scott Kenny said:
The USN got the lesson from having to try to stop kamikaze attacks, almost all their late war fighter variants had 4x 20mm instead of 6x .50cal.
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It's my impression that the US Navy actually had a more complex motivation when switching to cannon. Here's a quote originally posted by Tony Williams over on Aces High forum:

"As it is now, we have the 50-cal. gun which has reached its peak. The only improvements will be minor. The only good increase is to increase the number of guns. So it seems to be just about the right time to look for a better weapon. There are two possibilities here - the one we have and the one we might get shortly. The one we have is a 20-mm gun. I think very highly of it. In fact, it is one we have here, and it is one in hand. It won't do what the 60 will do, but we haven't got the 60, and we won't have it for a year. So, we are gradually working into all of our aircraft the 20-mm gun. To give you some idea of the 50 versus the 20 and dispel a lot of ideas that have bothered us, I would like to give you a comparison. When somebody goes from four 50's to two 20's, to the layman that means a decrease in fire power. Actually, quite the reverse is true. In the horsepower of the gun, one 20 is equal to three .50-calibers. In the actual rate of fire delivered at the target, one 20 equals three 50's; in kinetic energy at 500 yards, one 20 equals two and one half 50's.[N.B. This takes no account of the effect of the HE content of the 20mm shells]

That adds up to four 20's equaling twelve 50 calibers, judging by those standards. Of course you have other advantages of the 20. You have the much greater penetration of armor. The 20 will go through 3/4 inch of armor at 500 yards, while the .50 cal, will go through only .43. In addition to that you have one more great advantage - that is you can have longer and more frequent bursts without damage to the gun with the 20 than you can have from the .50 cal. That is important for the strafing airplane, because they are burning up their barrels and ruining their guns on one flight. Sometimes it is long before that one flight is over. They will come down with screaming barrels and get trigger happy, and then all the barrels are gone in one flight. It should not happen in a 20mm. Of course, you have disadvantages. You have a heavier installation, one-half as much ammunition for the same weight. Our standard ammunition in the Navy is 400 rounds in one gun. The Fleet has set up 30 seconds of fire as a minimum requirement for the .50 cal gun. We can't do that with the 20, so we give them 200 rounds. The 20 is lethal enough to get far more results out of that 200 rounds than the .50 ever will out of 400 rounds."

From: "USN Report of Joint Fighter Conference NAS Patuxent River". (October 1944)
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(As an aside, if you've watched the latest video of the "Greg's Aircraft" Youtube channel, he made the point there that no 0.50" barrels would be ruined in combat. Well, it seems to have happened often enough for the Navy to worry about it.)

Regards,

Henning (HoHun)
 
USN facing incoming Kamikazes - "Oh, pooh, we need to eliminate them before they hurt us!"

Royal Navy' response - "Man brooms! Sweep decks!"
 
Hi Sienar,

sienar said:
Is there any explanation of what the 60 would do that the 20 couldn't?
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The quote I provided is complete, so I'm afraid there's none.

However, I presume it's alluding to the expectations that an increased muzzle velocity will massively increase the hit probability of the firing fighter. There's another quote Tony provided which I am unfortunately unable to find, that stated that an X% increase in muzzle velocity will result in a Y% increase in probability of hit. With Y% being unreasonably high, in my opinion.

I was actually sort of wondering whether the Navy also had their doubts about the USAAF's expectations and thus had no reservations about switching to a theoretically inferior alternative without actually having to express these doubts. I am not aware of any great urgency on the Navy side to switch away from the 20 mm guns post-WW2, though admittedly that's a period I don't know all that much about.

Regards,

Henning (HoHun)
 
HoHun said:
I was actually sort of wondering whether the Navy also had their doubts about the USAAF's expectations and thus had no reservations about switching to a theoretically inferior alternative without actually having to express these doubts. I am not aware of any great urgency on the Navy side to switch away from the 20 mm guns post-WW2, though admittedly that's a period I don't know all that much about.
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The only change was from multiple individual 20mm guns as on F-8 and early A-7s to M61 gatlings as on A-7E. That said, it was an ammunition change as the Mk12 used the 20x110USN (developed from the HS.404 20mm cannon in WW2) and not the 20x102mm. The 20x110USN ammunition used a lighter projectile at higher velocity compared to the HS.404, 1010m/s versus 840-880m/s muzzle velocity. The 20x102mm ammunition is about the same muzzle velocity as the 20x110USN.
 
As far as I know the Navy was pretty satisfied with the 20mm Hispano once the problems were finally mostly resolved. They seemed fine with the Air Force leading development of aircraft guns while they pursued some further improvements of the Hispano design (resulting in the Colt Mark 12) in the short term.

I think someone in this thread mentioned it earlier but improved lead-computing gunsights would somewhat compensate for the lower velocity of the 20mm versus the .60 caliber option. Back when the USAAF decided that the .60 caliber MG was the answer to their needs they probably didn't foresee all of the improvements to gunsights that would occur, finally resulting in the radar-ranged models used over Korea.
 
I think that "not-invented-here" had a lot to do with USAAF Ordinance's attitude to 20-mm guns. The 20-mm Hispano was a French weapon reluctantly put into production under British pressure and adopted by the Navy.

The trajectory arguments strike me as after-the-fact justifications. The USAAF had no problem with the trajectory of the even lower-velocity 37-mm Oldsmobile guns. Moreover, higher velocity could hardly offset the obvious and probably inevitable problems arising from grossly oversized cartidges (especially the Hispano): broken parts, rapid wear, etc.

Moreover, USAAF Ordinance behaved like ballistics hobbyists, as if there were no urgent requirement to replace its preferred .50. Ordinance started with two fully developed, proven designs, the 20-mm Hispano and MG151/20, the former of which was already in production in the US (already plagued by unnecessary Ordinance-mandated modifications). Then it converted both to a caliber that, due to war experience, had already been turned down in England (in favor of 20-mm) and abandoned by the Luftwaffe (when the MG151/15 was turned in the MG151/20). Then it tried to do the impossible and convert the MG151/20 to use the longer and more powerful Hispano cartridge, in an instant undoing the thoughtful, engineering compromises that had made the gun successful in the first place.

To me, it seems astonishing that the .60-cal project was ever started, much less allowed to drag on through the end of the war.
 
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I was not an ordnance expert at 9 (or any age), but while at Eglin 51-54 dad brought home a box of inert .60 in a "0.50 cal" 200 round box. My mother ditched when I left for college. IIRC it looked very much like a Browning 50 necked up.
 
Hi,

drgondog said:
I was not an ordnance expert at 9 (or any age), but while at Eglin 51-54 dad brought home a box of inert .60 in a "0.50 cal" 200 round box. My mother ditched when I left for college. IIRC it looked very much like a Browning 50 necked up.
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Nice shiny toys, I'm sure it was a treat for a 9-year-old! :) I'm not quite familiar with the cartridge-related terms, but looking at Tony Williams' "Rapid Fire", the 0.60" cartridge certainly looks like the bigger and fatter brother of the 0.50" cartridge!

Tony also points out that the US pre-war developed a 23 x 139 mm cartridge and four different cannon prototype designs for air combat purposes. Somehow, I had always assumed that the 23 mm cannon specified for some pre-war aircraft would be imported Madsen guns, but according to "Rapid Fire", these used a less powerful 23 x 106 mm cartridge and were a disappointment in testing done in 1937, so I was obviously wrong in that assumption.

Had the US-designed 23 x 139 cannon worked out, they would probably have been a good choice for the P-47 too. However, I haven't checked Chinn's "Machine Guns" yet, I figure he might have something on these experimental guns.

Regards,

Henning (HoHun)
 
interesting that you mentioned Chinn
HoHun said:
Hi,



Nice shiny toys, I'm sure it was a treat for a 9-year-old! :) I'm not quite familiar with the cartridge-related terms, but looking at Tony Williams' "Rapid Fire", the 0.60" cartridge certainly looks like the bigger and fatter brother of the 0.50" cartridge!

Tony also points out that the US pre-war developed a 23 x 139 mm cartridge and four different cannon prototype designs for air combat purposes. Somehow, I had always assumed that the 23 mm cannon specified for some pre-war aircraft would be imported Madsen guns, but according to "Rapid Fire", these used a less powerful 23 x 106 mm cartridge and were a disappointment in testing done in 1937, so I was obviously wrong in that assumption.

Had the US-designed 23 x 139 cannon worked out, they would probably have been a good choice for the P-47 too. However, I haven't checked Chinn's "Machine Guns" yet, I figure he might have something on these experimental guns.

Regards,

Henning (HoHun)
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I'm pretty sure but not certain that the only change to the case was to neck up to the 60, shorten the case slightly to prevent a 50 cal from chambering, and keep the same headspace to make tooling for the barrels typical save bore size.

Interesting mention of Chinn. I was a project engineer tacking his 30mm cannon (IIRC WECOM 30, on the AH-J to replace the GE XM 188 20mm. We flight tested it in low hover at Yuma and it was scary to see the tail boom resonating to the fire rate (?450rpm). We should have noticed that the rate of fire was close to the natural frequency of the engine/rotor/airframe combination.

It never was considered after that. Circa 1972
 
Hi Bill,

drgondog said:
I'm pretty sure but not certain that the only change to the case was to neck up to the 60, shorten the case slightly to prevent a 50 cal from chambering, and keep the same headspace to make tooling for the barrels typical save bore size.
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Ah, I see. That sounds a lot like the German 15 × 96mm MG 151 cartridges ... if it weren't original German rounds, maybe they were relics from the start of the US 0.60" development path? I've now check Chinn's book, but he sort of implies all the various 0.60" guns used the same cartridge, though with the first one actually being based on a Hispano 20 mm cannon, I really wonder if I'm mabye misreading him. Probably we'd have to ask Tony Williams, but I haven't seen him post here in this forum much lately ...

Here's the "final" 0.60 cal cartridge in Chinn's book:

archive.org

The Machine Gun Volume 3 By George M Chinn : Free Download, Borrow, and Streaming : Internet Archive

693 pg
archive.org

However, Tony's "Rapid Fire" also shows pictures two additional, different US 0.60 cal cartridges (though both are fairly chunky as well).

For the sake of completeness, here a link showing downloadable versions of Chinn's work on machine guns:

Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine

archive.org archive.org

drgondog said:
We flight tested it in low hover at Yuma and it was scary to see the tail boom resonating to the fire rate (?450rpm). We should have noticed that the rate of fire was close to the natural frequency of the engine/rotor/airframe combination.
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That must have been absolutely terrifiying! And your project probably only very narrowly avoided providing a classic instructional video, to be shown to budding engineers right after the footage of the Tacoma Narrows Bridge collapse! ;-)

Regards,

Henning (HoHun)
 
HoHun said:
Hi Bill,



Ah, I see. That sounds a lot like the German 15 × 96mm MG 151 cartridges ... if it weren't original German rounds, maybe they were relics from the start of the US 0.60" development path? I've now check Chinn's book, but he sort of implies all the various 0.60" guns used the same cartridge, though with the first one actually being based on a Hispano 20 mm cannon, I really wonder if I'm mabye misreading him. Probably we'd have to ask Tony Williams, but I haven't seen him post here in this forum much lately ...

Here's the "final" 0.60 cal cartridge in Chinn's book:

archive.org

The Machine Gun Volume 3 By George M Chinn : Free Download, Borrow, and Streaming : Internet Archive

693 pg
archive.org

However, Tony's "Rapid Fire" also shows pictures two additional, different US 0.60 cal cartridges (though both are fairly chunky as well).

For the sake of completeness, here a link showing downloadable versions of Chinn's work on machine guns:

Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine

archive.org archive.org



That must have been absolutely terrifiying! And your project probably only very narrowly avoided providing a classic instructional video, to be shown to budding engineers right after the footage of the Tacoma Narrows Bridge collapse! ;-)

Regards,

Henning (HoHun)
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I wonder - Chinn was definitely an authority, but he was USMC, and his guidance for USAF may not have been the 'last word' for weapons development. I was too young to note the appearance of Gunval F-86s coming through Eglin and Tyndall AFB but the .60 cal testing was also in progress.
 
iverson said:
I think that "not-invented-here" had a lot to do with USAAF Ordinance's attitude to 20-mm guns. The 20-mm Hispano was a French weapon reluctantly put into production under British pressure and adopted by the Navy.

The trajectory arguments strike me as after-the-fact justifications. The USAAF had no problem with the trajectory of the even lower-velocity 37-mm Oldsmobile guns. Moreover, higher velocity could hardly offset the obvious and probably inevitable problems arising from grossly oversized cartidges (especially the Hispano): broken parts, rapid wear, etc.

Moreover, USAAF Ordinance behaved like ballistics hobbyists, as if there were no urgent requirement to replace its preferred .50. Ordinance started with two fully developed, proven designs, the 20-mm Hispano and MG151/20, the former of which was already in production in the US (already plagued by unnecessary Ordinance-mandated modifications). Then it converted both to a caliber that, due to war experience, had already been turned down in England (in favor of 20-mm) and abandoned by the Luftwaffe (when the MG151/15 was turned in the MG151/20). Then it tried to do the impossible and convert the MG151/20 to use the longer and more powerful Hispano cartridge, in an instant undoing the thoughtful, engineering compromises that had made the gun successful in the first place.

To me, it seems astonishing that the .60-cal project was ever started, much less allowed to drag on through the end of the war.
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The Hispano 'thing' relative to the Mustang was simply due to the fact that USN and AAF were splitting production 50/50 and production under license had just started. That said, it was a British order and the AAF had no problem with the installation of 4x20 on the Mk 1A in 1942, and did nothing to replace them when they suborned 58 as P-51-1-NA and converted most to Recon.

I do agree the USAAF was nigh impossible to accept the 20mm until Korea.

In retrospect, the USAF drive for the 0.60 cal was failure (IMO) to develop satisfactory HEI round for the 50, combined with early horror stories coming from Korea of F-86s smoking MiGs but not getting fires above 38-40K
 
sienar said:
Is there any explanation of what the 60 would do that the 20 couldn't?
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I think the question is more what the 60 could do than the 50. There was an attempt to load 50cal with HEI rounds during WW2 but deemed dangerous as fuzing was 'problematic' on the smaller round.
 

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