Thanks everyone for the info. I see the difference also between the cap of mine compared to the one in the photo. Mine is not rounded the same as the example Yoda has, instead mine is straight edged for about 20mm before it starts to round towards the top. The cap length itself measures 75mm in length. Besides a 10 stamped on the lower part of the cap, there is only 9687 stamped on the bottom. I see no other marks even after a nice clean up in the evapo-rust. Only black paint which (whats left) seems to be original.
Thanks, Shaky.
The case shoulder is also different. It's a lot more rounded on the older 3" cases. The 77mm cases have a more angular shoulder.The Comet was the only tank to use the 77mm gun. This used 17 pr projectiles with the old 3" 20 cwt AA gun cartridge case. 3" cases are easier to find than 77mm cases but though the same dimensionally, the crimping is different.
The Comet was the only tank to use the 77mm gun. This used 17 pr projectiles with the old 3" 20 cwt AA gun cartridge case. 3" cases are easier to find than 77mm cases but though the same dimensionally, the crimping is different.
Your 3" case is probably a US 3" case and though a similar length to 17 pr is a slimmer case. These were used in M10 tank destroyer.
Ram only used 2 pr in the Mk1 and 6 pr in the Mk 2. There were a few converted post war to 75mm, these used standard Sherman type ammo with the M18 case.
Tanks are not my cup of tea, but didn't the Sherman Firefly use also the 17 Pr gun ?
Yoda
The case shoulder is also different. It's a lot more rounded on the older 3" cases. The 77mm cases have a more angular shoulder.