On 13Jul2020 0717, xxxxxx@gmail.com wrote:

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> On Sun, Jul 12, 2020 at 2:38 PM Ethan McKinney
> <xxxxxx@gmail.com <mailto:xxxxxx@gmail.com>> wrote:
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>     On Sun, Jul 12, 2020 at 1:44 AM <xxxxxx@gmail.com
>     <mailto:xxxxxx@gmail.com>> wrote:
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>         On Sun, Jul 12, 2020 at 1:03 AM Ethan McKinney
>         <xxxxxx@gmail.com <mailto:xxxxxx@gmail.com>>
>         wrote:
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>         I thought your comparison with the 76mm was against the prior
>         75mm gun the Americans used. So it wasn't quite a 'same bore'
>         issue, but you get a bigger bore (ever so slightly) and a
>         higher muzzle velocity and that leads to reduced explosive
>         payload...
>
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>     The 76mm gun had a much longer barrel and the rounds had more
>     propellant, giving them a much higher velocity. The 1mm difference
>     was irrelevant to performance.
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> So, the gun was a higher velocity and that changes the performance,
> but reduces the efficacy of the HEAT round then? (vs the lower
> velocity 75mm?) Or were both the 75 and 76 limited in about the same
> way for how much HE you could pack in and thus HEAT performance might
> have differed much between the two guns?
>
> Or was the 76 capable of firing further but with a less effective HEAT
> warhead?

There are a couple of factors involved. One is that the faster a round
is spun, the less effective a HEAT round is (and higher velocities tend
to mean faster spin). The other is that higher velocities mean the shell
must have thicker walls, and this means a reduced payload, and thus less
effect from HEAT (and HE) shells.

Now, a high velocity gun like the 76mm can fire HEAT, etc. with a
reduced charge (and they normally do), but reduce it too much and the
ballistics will utterly suck, and even accuracy can suffer because of
inconsistent propellant combustion and other misbehaviour. Besides, with
a nice high velocity gun that is much bigger and heavier than a low
velocity gun, you do rather expect to get better range and accuracy even
from your HEAT (and those mean higher velocity).

>
>     Here's the dramatic comparison of the Sherman with 75mm, 76mm, and
>     105mm guns:
>     https://qph.fs.quoracdn.net/main-qimg-aa83244794fe858fbfdfd0c362a54450
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> Kinda fuzzy, but the middle one has a much longer barrel.
That's the 76mm gun.
>
> If the 75mm sherman had a non-HEAT anti-armour round and a HEAT one
> and so did the 76mm sherman, was the ratio of efficacy versus armour
> the same (HEAT vs. other round type) in both generations or variants
> of the Sherman?

I'm not sure if they actually had HEAT issued (and am too lazy to look
it up), but the 76mm's normal (kinetic) AP rounds were massively better
penetrators than the 75mm's, and the 76mm's HE rounds were considerably
weaker than the 75mm's and the same would've been the case for any HEAT
rounds.

--
Rupert Boleyn <xxxxxx@gmail.com>