USA: Early M4 hulls with L40 gun?

[DRG]

I'm looking into it so we can all stop talking about it.......I'm just not in any kind of hurry....12 years ago all the "regular" Shermans were weapon 47 ( L40 ). sometime between then and 2009 that changed on some models........don't know why but sometime between now and March 2017 I will sit down and figure out when and why it was changed

Don

[jp10]

Oh, we'll always find something to talk about, It seems many of us have a lot of time on our hands. Speaking of which, why aren't you in a hurry? What are you up to? Inquiring idiots have nothing better to do.

[MarkSheppard]

According to R.P. Hunnicutt's SHERMAN, the two 75mm guns installed on the M4 Medium Tanks were:

75mm M2 gun, which had the following measurements:

Length of Bore: 28.5 caliber
Length, Muzzle to rear face of breech: 31.1 caliber

and was installed in the T6 Prototype, and the first couple of Shermans off the production line. These are identifiable via the concentric counterweights installed on the end of the barrel; this is due to the gun mount being designed for the longer M3 gun, so the counterweights were a 'hackjob' to make the shorter M2 gun work in a mount designed for the longer M3.

75mm M3 gun, which had the following measurements:

Length of Bore: 37.5 caliber
Length, Muzzle to rear face of breech: 40.1 caliber

and was installed on the massively overwhelming majority of 75mm Shermans (99.99999%) built.

NOTE: The U.S. measured “calibre” as the length from the muzzle to the rear of the barrel (bore), while the Germans measured it from the muzzle to the rear of the breech. Thus, the US 75mm M3 gun would have a calibre of L37.5 under the US system and L40.1 under the German system.

This may be the cause of confusion; someone saw two differing sources, one measuring calibre via the German system (L40.1) and another via the US system (L37.5) and thought there were two 75mm guns with different calibre lengths in Shermans.

[Cross]

Originally Posted by MarkSheppard

According to R.P. Hunnicutt's SHERMAN, the two 75mm guns installed on the M4 Medium Tanks were:

75mm M2 gun, which had the following measurements:

Length of Bore: 28.5 caliber
Length, Muzzle to rear face of breech: 31.1 caliber

and was installed in the T6 Prototype, and the first couple of Shermans off the production line. These are identifiable via the concentric counterweights installed on the end of the barrel; this is due to the gun mount being designed for the longer M3 gun, so the counterweights were a 'hackjob' to make the shorter M2 gun work in a mount designed for the longer M3.

75mm M3 gun, which had the following measurements:

Length of Bore: 37.5 caliber
Length, Muzzle to rear face of breech: 40.1 caliber

and was installed on the massively overwhelming majority of 75mm Shermans (99.99999%) built.

NOTE: The U.S. measured “calibre” as the length from the muzzle to the rear of the barrel (bore), while the Germans measured it from the muzzle to the rear of the breech. Thus, the US 75mm M3 gun would have a calibre of L37.5 under the US system and L40.1 under the German system.

This may be the cause of confusion; someone saw two differing sources, one measuring calibre via the German system (L40.1) and another via the US system (L37.5) and thought there were two 75mm guns with different calibre lengths in Shermans.

Mark,

Does this mean the rear of the breech is in fact closest to the loader and not furthest from the loader?

I'm wondering if the US and British measured calibers by bore length, and the continental armies measured from muzzle to rear of breech, but this amounts to the same thing...

If the US Army used bore length, why does a primary US Army document refer to the 75mm M3 as L40?

If the bore was L37.5 it would be 281cm and if the rear of the breech (providing this is closest to loader) was L40 then this gives a breech length of 19cm. Can anyone confirm that this is a realistic breech length for a 75mm round?

Finally, if Hunnicutt is right that the 75mm M3 was in fact L37.5 and by German/continental measurements it was L40, then it should be left as L40 in the game because all the German L37 guns are given L40 in the game.



Cross

[Copernicus]

Originally Posted by Cross

Does this mean the rear of the breech is in fact closest to the loader and not furthest from the loader?

The breech is on the rear end of the cannon. Its front and rear are the same as for a cannon, generally, I would have thought.

These definitions from a 1922 Gunner's instruction manual seem to support my thinking on the matter:

https://books.google.com/books?id=Ss...page&q&f=false

See especially:
Bore
Breech
Breech, face of
Breech Reinforce

[MarkSheppard]

Originally Posted by Cross

I'm wondering if the US and British measured calibers by bore length, and the continental armies measured from muzzle to rear of breech, but this amounts to the same thing...

Pretty much.

If the US Army used bore length, why does a primary US Army document refer to the 75mm M3 as L40?

Which document? If you're referring to this one:



It's referring to the overall length of the gun, which would be very close to the length from the muzzle to breech face.

[cbo]

This might help (from Hunnicutt):



The difference between L/37 and L/40 is the difference between measurements C and E.

E = C+D

[DRG]

Hi Claus. Good to "see" you