USAAF 0.60" Cannon

[Shortround6]

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


Thank you

 

[Zipper730]

As for the Vulcan Cannon and Colt Mk.4: As I follow it

• The 0.60" used a 20mm casing necked down, and possibly shortened
• The Colt Mk-4 and Vulcan were then necked back to 20mm with the shortened casing and redesigned bullet shape?

 

[Shortround6]

As for the Vulcan Cannon and Colt Mk.4: As I follow it

• The 0.60" used a 20mm casing necked down, and possibly shortened
• The Colt Mk-4 and Vulcan were then necked back to 20mm with the shortened casing and redesigned bullet shape?

No, the .60 cal cartridge was not based on a 20mm. It was designed as a round for a man portable light anti-tank gun or heavy anti tank rifle. Much like the Russian 14.5mm x 114

From Anthony Williams website.BOOKS BY ANTHONY G WILLIAMS
The American .60 AT weapon was mounted on about the same tripod as a.50 cal machine gun.

 

[special ed]

In post 43 which is the spotter round used in sighting the 106 familiarization, All I remember from 1960 was that it was a shortened .50 but very accurate from the very short barrel.

 

[XBe02Drvr]

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.

The USAF seemed to have a penchant for the high performance, envelope-pushing approach while the Navy seemed to lean toward the practical and reliable.
Some of the advantages of the high velocity .60 round in air combat could be matched by the lower performance 20MM simply by drastically increasing its rate of fire. Hence the Vulcan. After seeing SR6's treatise on .60 ammo, I have a hard time envisioning a practical .60 Vulcan. The M61 put enough of a challenge on an airframe in terms of recoil, trim change, and CG shift, that the idea of a heavier, more powerful round just doesn't seem plausible. Unless you're going to adopt the A-10 approach of "a honking big gun with an airplane wrapped around it" you'll wind up with so much POI shift in the course of a burst that the advantages of your shorter flight time/flatter trajectory are likely cancelled. This leaves you with a plane that may not have the optimum balance of flight performance for ACM due to its "big gun" compromises.
At GE, we had to change the design and retrofit issued units of the Vulcan to capture and reload in the drum spent brass that was formerly ejected overboard. Pilots in Vietnam were complaining that the trim change due to CG shift and recoil was making bullet strike unpredictable, wasting ammunition, and perhaps putting friendly troops at risk. This mod shortened the learning curve for compensating for POI shift by "Kentucky windage" methods from half a combat tour to a quarter, or so we were told.
Cheers,
Wes

 

[Zipper730]

The USAF seemed to have a penchant for the high performance, envelope-pushing approach while the Navy seemed to lean toward the practical and reliable.

There is some truth to that, however there's no shame in pursuing practical and reliable. The gatling gun is advanced enough...

Some of the advantages of the high velocity .60 round in air combat could be matched by the lower performance 20MM simply by drastically increasing its rate of fire.

Actually the Vulcan started with 0.60...

 

[XBe02Drvr]

Actually the Vulcan started with 0.60...

I realize that, however it didn't continue, did it?
Cheers,
Wes

 

[Zipper730]

I realize that, however it didn't continue, did it?

True, but my point is why they started with that arrangement: There were already some people between 1946 and 1949 that were advocating for 20mm cannon

 

[XBe02Drvr]

True, but my point is why they started with that arrangement: There were already some people between 1946 and 1949 that were advocating for 20mm cannon

Ever hear of technological risk, where a great ground-breaking idea depends on too many undeveloped technical details that have a way of not shaping up as planned?
Remember, late 40s there were still a lot of piston aircraft not compatible with wing mounted or fuselage mounted gatlings, and early jets had problems with cannon fire disrupting intake airflow and causing compressor stalls and flameouts.
I'm guessing that when they started to design and build proof-of-concept mockup$ they di$covered $ome unfor$een problem$. The 20MM was more of a known quantity.
Cheers,
Wes

 

[GreenKnight121]

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.

Actually, the M1 Garand was part of a competition for both a new service rifle AND a new service rifle round.

The Army wanted an autoloader, and both Garand and John Pedersen (Remington's chief designer for years ) submitted rifles for consideration. They were originally both submitted in .276 caliber (designed by Pederson), and then also in .30 cal when the Army decided it wanted to stick to the .30-06 cartridge. The Garand rifle won the trials, and for good reason. Garand's was the better design. Pedersen developed a good cartridge, though. The Ordnance boards actually preferred the .276 Pederson round*, but were overruled, in part because the final decision was made in 1932 - the worst part of the Great Depression in the US, when the government was trying to cut as many costs/expenses as possible.

Aside from the "we've got lots of .30-06 ammo, and we don't want to complicate supply issues by having two different rounds at the platoon level", the .276 P. got a bad rap because Pederson goofed a little in making his prototype rifle - it required the cases of the .276 round to be wax-lubed externally in order to provide reliable extraction - while the same round in the Garand prototype did NOT require case lubing at all.

While what I have read indicates that the .30-06 in Pederson's rifle also required case lube, while the Garand's ability to operate both rounds unlubed worked in its favor.

.276 Pedersen Rifle



* The .276P, despite having a lighter bullet, actually had better long-range ballistics than the .30-06 - its flight path was flatter to between 800 and 900 yards, and had higher retained energy between 400 and 800 yards (past 800 yds the .30-06 does better, but that was mainly useful for snipers, not common infantry). Additionally, with a ~1/2" shorter case of smaller diameter than the .30-06, and the ability to hold 10 rounds in the Garand (vs the 8 allowed by the .30-06), more rounds of ammo could be carried for the same weight and volume in the can and in the Garand's magazine.

for those who think that the .280 british and the .276 pedersen were pipsqueak cartridges, in comparison to the .30-06 or the .303 british ...

 

[Zipper730]

Ever hear of technological risk

Yes, but the 20mm was already in use whereas the 15mm/0.60" was quite new. Maybe it's because the generals who were advocating for the 15mm/20mm seemed to be bomber generals might have played a role. I figure 20mm is a better option as it's more bang for your buck, the accuracy at typical firing ranges is close enough, and refire rate, while a little slower, doesn't really make too much of a difference as each round does 3-4 times more damage per shot.

Not sure how the 15mm compare to the 20mm in terms of damage capability to the 0.50. Frankly it seems the 20mm is a lower risk idea than the 0.60", though once you have a cannon based on a 0.60" under development, there might be some inertia.

 

[XBe02Drvr]

I figure 20mm is a better option as it's more bang for your buck, the accuracy at typical firing ranges is close enough, and refire rate, while a little slower, doesn't really make too much of a difference as each round does 3-4 times more damage per shot.

Really? IIRC, the projectile mass of the 15MM was nearly the same as the 20 used in the Vulcan, and it had way more velocity, making for equivalent or greater impact damage.
That heavy projectile and high velocity implies truly massive muzzle energy, with correspondingly brutal recoil forces and heavy structure required to withstand it. As it was, the relatively "tame" 20MM Vulcan operated at the limits of its structural strength. We saw some truly spectacular disintegrated guns come back from the test range.
Cheers,
Wes

 

[Zipper730]

Really?

I based the figures on the 0.50, I have no idea of the mass of the 0.60 compared to either the 0.50 or 20mm. If you have those figures, I wouldn't mind having them...

 

[XBe02Drvr]

I based the figures on the 0.50, I have no idea of the mass of the 0.60 compared to either the 0.50 or 20mm. If you have those figures, I wouldn't mind having them...

I believe if you look back through ShortRound6's posts you'll find them. Do your homework.
Cheers,
Wes

 

[Zipper730]

I was doing some research on the 0.60 T17. It apparently was inspired by the earlier 0.60 T1, and the German MG151. That said, did they not realize that the Germans were already switching over to the MG151/20 (a 20mm cannon variant)?

 

[Shortround6]

The US Army (or ordnance ) had an obsession with high velocity. It makes it much easier to get hits in defection shooting. The German MG 151/20 wasn't anywhere near the velocity they were looking for. In hindsight the velocities they were looking for had some problems of their own.

 

[Zipper730]

The US Army (or ordnance) had an obsession with high velocity.

Out of curiosity, what disadvantages come with high velocity?

The German MG 151/20 wasn't anywhere near the velocity they were looking for.

The MG151 didn't have the velocity of the T17, but the point is that the Germans weren't happy with the MG151 and necked it up.

 

[Shortround6]

Out of curiosity, what disadvantages come with high velocity?

Large guns.
Heavy ammo.
Very short barrel life.
US Pilots were advised to fire only 75 rounds through a cold barrel before stopping to let it cool and only about 25 rounds per minute after that.
Obviously not practical in real combat but a sure indicator that barrel life was not good. High velocity guns funnel an awful lot of high temperature gas through small diameter barrels.

The MG151 didn't have the velocity of the T17, but the point is that the Germans weren't happy with the MG151 and necked it up.

The Germans traded the hitting advantage of the 15mm cartridge for the greater destructive ability of the heavier projectiles. They changed course.

 

[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.

They favored the muzzle velocity that much eh?

Large guns. Heavy ammo. Very short barrel life.

And the guns have to be big because of the higher chamber pressures, and the heavier ammo is the gunpowder?

US Pilots were advised to fire only 75 rounds through a cold barrel before stopping to let it cool and only about 25 rounds per minute after that.

The 0.60 had that kind of demands on it?

The Germans traded the hitting advantage of the 15mm cartridge for the greater destructive ability of the heavier projectiles. They changed course.

We didn't know this by 1944?

I did some calculations for impact forces on projectiles and got the following figures using the following formula: Impact force = projectile weight (grains) x velocity (fps)^2 / 450437...

• 0.50 BMG: 10000-15000 foot-pounds (I didn't calculate that but it was based on various figures -- I don't know how much the rounds differed from WWII)
• 0.60 (15.2x114mm): 33951 foot-pounds
• 20x110mm: 37683 foot-pounds
• 37mm M4: 83322.6 foot-pounds
• 37mm M9: 268263.25 (not sure if I miscalculated that one)
• Vickers-S (40x158mm): 179026.6

The 20mm was 11% more powerful. Not as much as I'd have thought believe it or not. This of course just counts impact force

 

[Shortround6]

And the guns have to be big because of the higher chamber pressures, and the heavier ammo is the gunpowder?

The guns have to be bigger to handle the longer, fatter cartridge cases. The weight of the gunpowder is nominal compared to weight of the brass cartridge case to hold it.

The 0.60 had that kind of demands on it?

No, the US .50 had those restrictions, at least in early manuals. the .60 would have been worse.
Please note that they started chrome plating the bores of the .50 in 1944 I believe, which gave longer life. They may have tried to use stelite inserts They did use them on later machine guns.