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A Question on US 76mm HE Rounds


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LegioCI #1 Posted May 08 2016 - 12:09

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One of the big reasons that slowed the introduction of the US 76mm gun upgrade for the Sherman was its inferior HE round. Since the 76mm had a higher muzzle velocity and chamber pressures it required a thicker casing for the HE charge which meant that there was less explosive filler which translates to far less boom when the round hits the target.

 

What I never understood, was why 76mm HE rounds weren't just fired with at a lower chamber pressure/muzzle velocity? Assuming there wasn't some catastrophically bad reason for doing so, could firing the 76mm HE rounds at a lower velocity have allowed for a larger explosive charge for the round?


Edited by LegioCI, May 08 2016 - 12:12.


Spooooooooooooooooooooon #2 Posted May 08 2016 - 12:20

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My uneducated guess would be they needed consistent pressures on different types of rounds to keep the sighting system on target. 

The_Chieftain #3 Posted May 09 2016 - 20:25

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My guess, and it's just a guess, is that the 76mm needed a set impulse in order to have sufficient recoil to operate the breech: If they fired the same projectile at a lower velocity, it may not have had sufficient rearward force. I don't off the top of my head remember seeing anything in the documentation about a low velocity round.



MarcAFK #4 Posted Jun 23 2016 - 10:58

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I've wondered about this, Wikipedia isn't being entirely helpful as the page for both the 75mm M3 and 76mm M1 show the same M42 a1 HE shells, which I'm sure weren't compatible. Did the US use the same ammunition designation for different Calibers? The page for the 76 mm shows a table which states the cubic capacity of M5 and M1 rounds and then offers the capacity of the 75mmM3 as well. Those numbers are:
76mm M1 M42 HE :140 cubic inch.
3 inch M5 HE : 203 cubic inch
75 mm M3 M48 HE:80 cubic inch
17 pounder 300 cubic inch.
It seems that the round was significantly larger than the 75 mm gun so should have carried a larger filler, but obviously wasn't as capable as a 3 inch M5 round. It says the M42 had a 390gram HE filler,but I can't seem to find information about the filler of the other rounds.
However refuting the chieftans suggestion I submit that the smoke rounds fired from an M1 are lighter, and have vastly lower range and muzzle velocity,  so I'm assuming the chamber pressure must have been lower too.

Anlushac11 #5 Posted Jun 23 2016 - 11:10

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The various US 76.2mm guns all fired same projectile, more or less. What is different is the casing that held the propellant. That had to match the chamber of the gun firing said round.

 

Example...Brit 77mm and Brit 17lbr were both 76.2mm and fired same projectile but the rounds were not interchangeable because the casings were different. 


Edited by Anlushac11, Jun 23 2016 - 11:11.


Walter_Sobchak #6 Posted Jun 28 2016 - 01:37

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Here is some data comparing the effectiveness of 76mm shells and 75mm shells.  Notice that they regard the 3 inch shell and the 76mm shell as the same for purposes of HE effectiveness.

 

Comparison of Performance of 75mm and 76mm tank gun ammo



Death_Bot_3001 #7 Posted Jul 25 2016 - 19:36

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There are minor differences between the 2 but the big one is that the 76mm is a much lighter casting even though it was originally longer then the 75mm. With its shorted design it still maintained the same performance of the 75mm. Funny since they were outgunned and needed more pen later in the war they still insisted in cutting almost a full meter of gun out so it would have consistent performance as it's processor. Not  the best answer I know but hey...

Anlushac11 #8 Posted Jul 25 2016 - 21:23

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View PostDeath_Bot_3001, on Jul 25 2016 - 13:36, said:

With its shorted design it still maintained the same performance of the 75mm. Funny since they were outgunned and needed more pen later in the war they still insisted in cutting almost a full meter of gun out so it would have consistent performance as it's processor. Not  the best answer I know but hey...

 

The shortening of the 76.2mm gun barrels had more to do with getting the gun balanced in turrets.




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