USAAF 0.60" Cannon

[Zipper730]

AFAIK, first US aerial 60cal gun is T17 and it is the copied gun of German MG151/15. So... IMO, 60cal was begun, when they tried copying 15mm gun with imperial unit.

You can find futher information about in this link.

Springfield Armory Museum - Collection Record,

General Arnold was spearheading the USAAF variant right?

The why is easy; jet propulsion. Nazi's were flying faster aircraft and that meant actual ballistic efficiency times were becoming very short. The Air Corp needed something that launches a heavier bullet at faster speeds to extend target coverage time, deliver greater damage with the heavier bullet, and when the bullet is loaded this explosives a single hit might actually bring about a downed enemy jet.

Though this might sound silly: Why did the USN keep developing 20mm? They wanted 20mm since WWII and had continued along this pathway (though they evaluated the 0.60).

After several months of consideration and thousands of rounds fired for effect, the decision was made to improve existing 20mm armaments and shelve the concept of a .60" machine gun.

Except for the Vulcan Cannon, which continued for years it seemed...

 

[Shortround6]

The why is easy; jet propulsion. Nazi's were flying faster aircraft and that meant actual ballistic efficiency times were becoming very short. The Air Corp needed something that launches a heavier bullet at faster speeds to extend target coverage time, deliver greater damage with the heavier bullet, and when the bullet is loaded this explosives a single hit might actually bring about a downed enemy jet.
The problems with this new round was that it used the current 20mm case and just necked it down to 15mm. Results weren't as important as the safety concerns brought about with someone loading up a 20mm cannon with 15mm ammo. After several months of consideration and thousands of rounds fired for effect, the decision was made to improve existing 20mm armaments and shelve the concept of a .60" machine gun.

The US was working on the .60 cal machine gun before they ran into the German jets. The T-17 was the 2nd attempt at .60 cal machine gun and the project started in Sept/Oct of 1942.
The 1st attempt was the 15 mm Bendix gun which was a modified 20mm Hispano. By the fall of 1943 the T-17 project was on the T17E3 model (4th version of the T17) and would continue on to several more versions. There was also a T18 series and a T19 series and in July of 1944 The Gazda Engineering Co. company got a contract for a T31 series. This took about 11 months to produce a gun that broke after about 40 shots but shows that interest in a .60 cal machine gun started well before there were any encounters with German jets.
The .60 cal cartridge was actually a pre war (at least pre 1941) anti-tank gun cartridge.
It is almost impossible to load a necked up cartridge into a smaller caliber chamber without some real energetic work to fully close the bolt. It is quite possible to load a larger caliber round into a smaller caliber chamber IF the large caliber round is shorter in overall length. Like you can put an 8 X 57 Mauser round in a 7.62 X 63 (30-06) chamber because the fatter bullet is still in the neck area of the longer cartridge. It doesn't work the other way around because the shoulder on the 30-06 case will hit the shoulder of the chamber with bolt still 5-6 mm short of the bolt closing.
There was a .60 cartridge (15mm) based on the 20mm Hispano but that went into a different series of guns as was not favoured as it was lower powered than the .60 cal anti rank round. (smaller in diameter for less powder capacity.)

 

[Zipper730]

The US was working on the .60 cal machine gun before they ran into the German jets.

Interesting...

The 1st attempt was the 15 mm Bendix gun which was a modified 20mm Hispano.

Why not just use the Hispano? Most of the problems with the 20mm were basically our own doing (if it ain't broke don't fix it).

The .60 cal cartridge was actually a pre war (at least pre 1941) anti-tank gun cartridge.

How did they compare in velocity?

 

[Shortround6]

Interesting...
Why not just use the Hispano? Most of the problems with the 20mm were basically our own doing (if it ain't broke don't fix it).
How did they compare in velocity?

The US was looking for much higher velocity than they could get from the 20mm Hispano.

.50 cal on left and .60 cal on right.
They also necked the big case down to .50 cal for even more velocity.
There was also a 20 Hispano round necked down to .60 cal.

Cropped from picture on Anthony Williams website BOOKS BY ANTHONY G WILLIAMS
Cartridge on left is .55 Boys anti-tank rifle, the 15.2 X 114 is the .60 cal, the 12.7 x 114 in the .60 cal necked to .50 cal, the 12.7 X 120 is the 20mm Hispano necked to .50 cal and the 16 X 99 is the .50 cal Browning necked up to 16mm.

 

[Zipper730]

The US was looking for much higher velocity than they could get from the 20mm Hispano.

The USAAF/USAF was, the USN didn't seem to be. Why the difference?

 

[Shortround6]

The USAAF/USAF was, the USN didn't seem to be. Why the difference?

The USN didn't do a lot of gun development. At least not until late in the war or post war.
To avoid duplicate programs and waste/spending the US Ordnance Dept (a branch of the army) handled most of the weapons that both services could use. Small arms and machine guns. Somebody in the Navy is going to have to decide to use some of their not unlimited R& D funds to pay for aircraft gun development that the Army (and post war the Air Force) was already doing instead of just pigging backing production contracts onto the Army/Air Force contracts.
If they can't standardize on things you wind up with situations like the Japanese had with the Army and Navy using different guns and different ammo with problems in logistics.

The Army may have had a valid theory with their high velocity guns. Execution was a problem. The development of the gyro gunsight achieved a lot of the goals of the high velocity guns (much improved hit rate in deflection shooting).

It could take 4-6 years (and longer) to bring a gun from initial concept to a finished, reliable service weapon. The contract that lead to the M-61 Vulcan gun was issued in 1946, first guns weren't test fired until 1949, and first real service use wasn't until 1959. Obviously there can be an ebb and flow of enthusiasm for funding for certain projects.

 

[gomwolf]

General Arnold was spearheading the USAAF variant right?


Though this might sound silly: Why did the USN keep developing 20mm? They wanted 20mm since WWII and had continued along this pathway (though they evaluated the 0.60).
Except for the Vulcan Cannon, which continued for years it seemed...

AFAIK, they started copying MG151/15 at 1942, so... general Arnold maybe involved with this.

 

[special ed]

If I remember correctly, back in 1960 when the M-61 was the latest thing, we were told the concept came from German data, an electric motor driven multi barrel gun.

 

[Zipper730]

If I remember correctly, back in 1960 when the M-61 was the latest thing, we were told the concept came from German data, an electric motor driven multi barrel gun.

I thought the idea was an auto-revolver

 

[vikingBerserker]

The US was looking for much higher velocity than they could get from the 20mm Hispano.
View attachment 513681
.50 cal on left and .60 cal on right.
They also necked the big case down to .50 cal for even more velocity.
There was also a 20 Hispano round necked down to .60 cal.
View attachment 513680Cropped from picture on Anthony Williams website BOOKS BY ANTHONY G WILLIAMS
Cartridge on left is .55 Boys anti-tank rifle, the 15.2 X 114 is the .60 cal, the 12.7 x 114 in the .60 cal necked to .50 cal, the 12.7 X 120 is the 20mm Hispano necked to .50 cal and the 16 X 99 is the .50 cal Browning necked up to 16mm.

Holy crap that's a big round!

 

[special ed]

Not as big as a 30mm

 

[Shortround6]

If I remember correctly, back in 1960 when the M-61 was the latest thing, we were told the concept came from German data, an electric motor driven multi barrel gun.

Dr Gatling himself may have put an electric motor on a Gatling gun back in the 1890s (couple of pulleys and belt replacing the hand crank?) so the idea was not exactly new.
There was a German gun that did use multiple rotating barrels that was tried in WW I but used totally different lock work and feed setup.

 

[special ed]

Reference to the German ancestry of the M-61, my notes from my instructor indicate Mauser MG 213. A quick look at wiki says there was such a gun/ Perhaps shortround or wurger or johnbr can find pictures.

 

[tomo pauk]

MG 213 - a revolver gun/cannon, that utilized multiple chambers (to feed and fire ammo) and just one barrel. Post-war and modern spin offs include the ADEN, DEFA, M39, BK 27 and the big 35-1000.
The M61 was gatling gun/cannon (duh) that used multiple barrels that rotated around the common axis. Several gating guns were made, in calibers ranging from 7.62 NATO (the 'Minigun', well known from the 'Predator' movie) to 30mm (from USA, Russia, even China). Number of barrels being between 3 and 7, generaly more barrels = greater RoF. The American 30mm gatling was used on the A-10s and as business end of the Goalkeeper, the naval CIWS.

 

[Shortround6]

To further differentiate, the Revolver cannon has one firing mechanism and one breech block. The Gatling gun has one breechblock and firing mechanism for each barrel.

Gatling gun

Így működött a kurblis pusztító - para bellum
Note that this animation shows the bolt travel is controlled by the rear roller and the cam track and the firing pin is controlled by the forward roller and cam track. As the bolt is moved forward the firing pit is caught and held to the rear and when the barrel reaches the correct spot in the rotation the firing pin is released by the cam track. I would note that Gatling guns are unaffected by dud rounds (but not hang fires) and any dud rounds are simply extracted and dumped out (sent back to drum) as the Gatling gun does not use the power the gun firing to operate the the action (mostly, a few modern guns were modified to tap gas of the barrels to eliminate the electric or hydraulic drive motors.

 

[fliger747]

The 1944 Joint Fighter Conference indicates a lot of interest in the .60 as the gun of the future though the effectiveness of the 20 mm was praised as being maybe 4X better than the 50 BMG. Never arrived during the war, the .60 and fell by the wayside in the resulting lack of interest in many things post war. Even for land forces, cartridge selection becomes a contentious affair. The first M1 Garand was developed in a .270 cartridge and might have been a better round for WWII, but Mc Arthur, Army Chief of Staff vetoed the idea as millions of 30.06 rounds were still in stores after WWI.

The cartridge follies continue to these days.

 

[Shortround6]

The .60 had a few problems that are never really mentioned.
One can argue about the .50 vs 20mm to some extent but the .60 had most of the disadvantages of the 20mm (guns and ammo weighed about what the 20mm guns and ammo did, ie a plane could only carry four .60 cal guns if could carry four 20mm and ammo would be in proportion) and none of the advantages of the .50 cal. (lighter weight and higher rate of fire) leaving it's high velocity/short time of flight as it's only real advantage. Unfortunately this is going to cost in barrel life. The .50 was bad enough as it was, trying to funnel all of the hit gasses from that big .60 cal case though a .60 cal barrel without destroying the rifling in short order required metallurgy and propellent technology that didn't exist in WW II.
The US started chrome plating the bores on .50 cal machine guns in 1944 (?) which helped. Other nations had chrome plated small arms earlier but getting uniform chrome plating inside a long narrow tube is not easy. The US was also working on stellite inserts and/or rifled barrel liners to fight burned out barrels as these work better than chrome plating.
With the improvement in gun sights the need for high velocity to improve the chances of defection shooting dropped and as things shifted to the cold war and large Russian bombers became the primary aerial target the lack of hitting power/target effect of the .60 compared to the 20mm certainly didn't favor the .60 cal.

 

[Shortround6]

A WW I German gun that is sometimes confused with the Gatling is the Fokker-Leimberger gun.

A good example of "thinking outside the box" and while it did eliminate a number of parts/problems in ordinary guns it introduced a few of it's own.
It was not feed by an ordinary belt but something that is sometimes translated as a "tape".
As shown in figures 2 and 6 in drawing the weapon did NOT extract the cartridges from the belt/tape and then stuff them in the chamber. Instead the outer half of the chamber in each barrel was cut away and the drum under the barrel assembly was machined with matching chamber "halves". with both units rotating at the same speed the belt/tape was pulled through (no extra belt feed needed?) the top and bottom halves of the chamber sandwiched the cartridge sort of nutcracker fashion as the hammer fired the gun and the belt/tape went out the otherside with the fired cartridge case still in it's pocket.
This eliminated a whole bunch of parts an ordinary machinegun use to pull cartridges out belts, it eliminated normal extractors and ejectors and their associated springs and pins.
However it introduced a gap not only at the front of the chamber where high pressure gas could escape but they were never going to get both sides (or top and bottom) of the chamber to match closely enough (especially with the notch/gap needed for the belt/tape) to prevent occasional cases from splitting up the side along the joint. The more this happens the worse it gets as the high pressure, high temperature gas flame cuts the surfaces and makes the gap a tiny bit bigger with each occurance.
you also have the problem of what to do with the part of the belt/tape with the fired cases. At the advertised rate of fire you have 120 rounds worth of belt/tape and empties coming back out of the gun all fastened together. What sort of box/drum/container is going to be needed to hold it?

 

[XBe02Drvr]

As the bolt is moved forward the firing pit is caught and held to the rear and when the barrel reaches the correct spot in the rotation the firing pin is released by the cam track.

Very interesting. When I worked at GE in 69/70 there were no Vulcans to be seen with impact primer ignition as seen in the animation. They all had electric ignition primers in the cartridges and the firing pin/contact slid forward with the bolt and was pressed back against its spring when it came in contact with the primer as the bolt locked. This rearward motion put it in contact with a voltage source which fired the primer. The Minis (7.62) and Micros (5.56) still used impact ignition as depicted in the animation.
Cheers,
Wes

 

[Zipper730]

The 1944 Joint Fighter Conference indicates a lot of interest in the .60 as the gun of the future though the effectiveness of the 20 mm was praised as being maybe 4X better than the 50 BMG. Never arrived during the war, the .60 and fell by the wayside in the resulting lack of interest in many things post war.

So the interest was faster rate of fire and better ballistics?

It's fascinating how the USAF retained an interest in the 0.60" to a varying degree (the bomber generals seemed to grasp the 20mm's potential; the M61 Vulcan was designed around the 0.60 at first) until about 1952, while the USN pretty quickly settled on the 20mm.