British Big Gun

[drgslyr]

I cannot find the answer to this question. All sources agree that the British 17-pounder that was fitted to the M4 was much more powerful than the 75mm gun used by the Americans, but nobody explains why it was so much more powerful. The 17-pounder was 76.2mm, so it doesn't seem that much bigger. Was the length of the barrel just longer than that of the Sherman's, or did the British use a different type of shell? Was it a combination of both or is there some other explanation?

[von Poop]

Good question,
From memory the muzzle velocity and weight of shell of the 17pdr was about a third more than the Soviet 76.2, high muzzle velocity (though not too high) leads to greater accuracy and harder hit, also in the last years of the war there was limited availability of discarding sabot ammo (APDS), looking at this picture it was a hefty shell firing an advanced projectile:

British Tank rounds left to right: 2pdr, 6pdr APDS, 75mm (Sherman), 17pdr APDS, 77mm (Comet), 3" and 95mm CS.

from:http://www.flamesofwar.com/Article.asp?ArticleID=324, I reccomend a look there and follow the link to 'Guns versus armour' at the bottom.
Good luck,
Adam.

[Owen]

penetration chart here.........http://gva.freeweb.hu/weapons/british_guns5.html

[drgslyr]

Thanks for the answer and links guys! They were a big help

The answer seems to lie mainly with the fact that the 17-pounder gun used an APDS round. Given that the British had such a hard time fitting the cannon onto the M4 though, I'm surprised they didn't just develop a shell that could be used in the standard 75mm gun. It seems that this would have been easier and it would have had the added bonus of keeping the enemy guessing as to which tanks were using the more lethal rounds (considering German tank crews were instructed to target the Fireflys first because they were the biggest threat).

Of course, if the Sherman's 75mm gun was significantly shorter than the barrel used for the 17-pounder(?), then the argument would become moot because I suppose you would have to sacrifice too much in muzzle velocity. Shows how much I know.

Thaks again!

[Glider]

The Sherman 75mm was initially a straight copy of the French WW1 75mm gun. Hence the difficulty in upgrading the Anti Tank ability

[kfz]

[quote=drgslyr] Given that the British had such a hard time fitting the cannon onto the M4 though,
quote]


Did they? I thought the Sherman with the 17pdr was a last ditch attempt when the samegun in the valintine and other Bristch models where failure.

The 17pdr was designed from the ground up to be tank and conventional carrige mounted??????

[von Poop]

They did indeed have a hell of a time fitting the 17pdr into Sherman, look at the size of the gun relative to the turret & ring, eventually had to mount the gun 'sideways', if you look inside a Firefly turret.... it's a mess.

[MikB]

You can see from the cartridges shown earlier that the 17pdr case has much greater capacity than the standard 75, meaning much more kinetic energy is available from the propellant charge. This bigger charge also requires a longer barrel to burn it in - 58 calibres long as compared to the 40 calibre long 75mm. The result with ordinary APCBC (full weight AP shot with a streamlining 'ballistic' cap) was MV of about 2950 - 3000 fps against 2030 - 2050 for the 75. Since kinetic energy is what pierces armour, and this increases with the square of velocity, that of the 17 pdr was more than twice the 75's.

The APDS traded projectile weight for even more velocity, and nearly doubled the penetration again.

What I've often wondered is why no-one tried to improve the performance of the 75 with APDS, since it was undoubtedly a handy gun for tank battles in woods and towns, especially with the Sherman's exceptionally fast turret traverse. Perhaps it was not possible to come up with a propellant that would burn consistently enough in the short barrel.

The performance of the 17 pdr Sherman Fireflies was very good. The German Tiger tank ace Wittmann was probably killed in a shootout with Fireflies, and I believe the Americans unsuccessfully asked for some. With the clout of a Tiger or Panther and better agility than either, their vulnerability was somewhat offset.

Regards,
MikB