[ops33]

Thanks but how does 1 mm make such a difference?

[JerseyanExile]

On it’s own, not that much. However, the construction of the two guns was radically different - for starters, the 75mm was only a 40 caliber gun, the 76mm 52. The barrel was almost twice as long, and the gun had an entirely new type of high-velocity shell.

[Lazamataz]

Thanks but how does 1 mm make such a difference?

You should know this, being AF! One mm doesn't make a difference, but usually, with a new round you will have a new penetrator and a different case/propellant. THAT is where your difference comes in to play...