Quote:
Marek_Tucan said:
Why there was no APDS shot for 75mm? With some supercharge it might be pretty effective and give 75mm armed tanks somethign to fire at German heavies... Was it because APDS was developped by artillery for antitank guns and armored corps got it just as a by-product?
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Dont know why, but it could well have had to do with the somewhat convoluted development history of British tank guns. They had always been high-pressure, high-velocity anti-tank weapons and when they were looking for guns for the next generation of tanks in 1942, it would appear that the weapons of choice were the 17-pdr and Vickers-Armstrongs high velocity 75mm L/50 gun. As the latter turned out to be too big for the Cromwell, something had to be cooked up fast and Vickers-Armstrong could offer a medium velocity 75mm that fired US ammunition and fitted in the 6-pdr mount. I dont think it was ever considered anything but a stop-gap solution until something better was on offer.
As the gun was a temporary measure and fired US ammunition, it might not have been considered worth the effort to spend APDS development time on it, particularily since the Americans were apparently working on the T45 HVAP round anyway.
Add to that the limited advantages you would get from APDS/HVAP in the 75mm gun. APDS would probably not be a much better performer than the experimental US T45 HVAP round, except at longer distances, which wouldn't matter because early APDS was so inaccurate anyway. Of course 117mm penetration is a lot compared with 66mm, but not enough to make a real difference in combat and a far cry from the 208mm of the 17-pdr or even the 157mm of the 76mm US gun.
Add to that the fact that APDS/HVAP was always in short supply, something which would probably have been clear even as APDS/HVAP was developed. Those rounds used strategic materials that was needed for many other purposes and always in short supply, even for the allies.
Then there is the issue of the guns design raised by Kesh. I dont know how much pressure the UK 75mm could handle, but the max. powder pressure of the US 75mm gun was 38,000 PSI, the same as the long US 3" M7 but less than the 43,000 PSI of the 76mm M1A1 tank gun. And a lot less than the always "hot" UK guns, the 2-pdr producing 44,800 PSI, the 6-pdr. 46,000 PSI and the 17-pdr 47,000 PSI.
The M7 and M1A1 fired the same projectiles and achieved the same performance, but the M1A1 did so using a a smaller cartridge with a hotter load, apparently.
The chamber capaciy of the US 75mm was 88 CUI vs 142 CUI of the M1A1 and nowhere near the 300 CUI of the 17-pdr. It was even smaller than the 6-pdr at 100 CUI.
I'm no ballistician, but I'd guess that the combination of a small chamber, shortish barrel and inability to raise pressure to the required levels made it rather pointless to persue APDS/HVAP for the 75mm gun.
Perhaps a similar argument could be made with regards to HEAT. That did not require velocity, but a 75mm HEAT would only raise penetration to 75-90mm, at least if you assume performance on par with German 75mm HEAT rounds. Better than the 66mm of the M61 APC(BC) at 500 yards, but still not significantly so.
cbo