Sherman MkVc Firefly 17-pdr question
 

To the Sherman gurus ....

Why did the Brits need to reconfigure the 17-pdr with a horizontal sliding block breech for the Sherman Firefly when the production AT gun used a vertical sliding block? Was it, as Wiked-pedia states, due to internal space considerations?

Was this same horizontal breech configuration used in all other 17-pdr-equipped Brit tanks or was the vertical block of the AT gun used in some? The Centurion Mks 1 & 2 used the 17-pdr Mk.6 which had the horizontal sliding block breech.

Thanks

Mike

In the confined space of a tank turret a horizontal breech makes complete sense as it allows full range of motion in elevation and depression of the gun.

I agree, and can see a number of advantages for a horizontal breech block, particularly with the block sliding away from the loaders position, which would then make the handling of the large 17-pdr round easier to move sideways into alignment with the chamber.

The elevation of the gun would be restricted by, among other things, the design of the mantlet/turret external interface and internally what is located beneath the downward swing of the breech. So with regard to internal room, it would depend on the turret basket depth and stowage design. Was this so cramped in the Sherman as to dictate the manufacture, in the middle of a war, of a different breech when the vertical sliding breech was already in production?

Mike

Distance breech ring to turret ring?
 

I've had another thought: what is the distance from the back of the 17-pdr breech block to the turret ring on a Sherman Firefly, compared to the length of the longest 17-pdr round?

Maybe that was the restricting feature - the extra 8 or so inches further back required to move a 17-pdr round into alignment with the chamber of a vertical breech, compared to a horizontal breech.

Thoughts?

Mike

You also have to factor in the human fit and ergonomics, I think there is a bit more to making the machine fit the man (or man fits machine) then turning the 17 pdr gun by 90°, there is a stowage reconfiguration and no doubt the breech lever is different.

Hi James,

I'm sure it was not as simple as just the distance between breech ring and turret ring, but I have to start somewhere in getting to a better idea than just wiked-pedias blanket 'internal space considerations' and I don't have access to any of the original development reports.

Mike

IIRC this has some answers: https://www.youtube.com/watch?v=__Y8YJeas4I though I don’t feel like watching all of it again to find them :)

Thanks Jakko, the visuals certainly provide some good information.

Mike

Mike

Horizontal sliding breech on Mk4 and Mk7 which went into Firefly.

The only components which are the same as AT gun are Barrel and Muzzle Brake (assuming you have the Mk1 to Mk7 barrel).

The difference between the Mk4 and Mk7 is the breech spring for the semi-auto mechanism - the earlier version was prone to sticking.

The 17pdr in the Mk1 Centurion is pretty much the same gun as the Firefly too.

Hope this helps

Tim