Effect of AP cap on high obliquity performance of british AP shot

Machinery of War Discussion Historical Discussion
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Each data point represents the respective BL against the same plate determined using AP and APCBC 2pdr and 6pdr shells.
Although there is considerable dispersion in the data, we can see that, on average, the capped AP shot of the same mass (sans the cap) has a higher ballistic limit(about +3%) for the same target.

40° 50° and 60° data

40° only

50° only

60° only

You can use this knowledge next time you see “experts” trying to explain to you how the AP cap was supposed to “bite” into the armour and improve high obliquity performance.

Source: “Report M.7000 A/11 No.1
Department of tank design armour branch. APCBC Shot at oblique impact of machinable quality plate.”

Link: Whelmy - 2,6 and 17 pdr AP and APCBC vs slope - Album on Imgur

Edit: Here is the comparison of a capped and uncapped shell of the same mass at low obliquity:

Spoiler

Cap Effect
Cap Effect1831×945 140 KB

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So basically uncapped AP round with the same penetrator weight as an APC round will have slightly better penetration against oblique armor? It’s a bit difficult to understand the graphs but that’s my take-away.

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Exactly. Well, strictly speaking, at least if the steel they’re made of has the same physical properties as the british shot here. Haven’t done much comparison of APCBC vs AP shells of other nations.
British 2pdr and 6pdr capped shot are somewhat unique in regard that, without their caps and windshields, they have the same exact weight and shape as the uncapped shot.
For more orthodox APCBC designs, the shell without its cap is not only lighter but shorter as well, which brings in the mix the effects of L/D ratio, which I dont know how to account for.

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