Snippets found in the kitchen: 20-pdr APDS and t/d ratio

[John D Salt]

I have been trying to clear some of the accumulated rubbish out of the kitchen, much of which is paper. One item swept up during the great clearing of the worktop was a notebook incuding a couple of snippets from National Archive visits many years ago. As I have just typed these up, I see no good reason not to inflict them on a wider public, as there are perhaps two or three people here who share my fascination with the phenomenon of armour penetration.

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DEFE 15/367 “Effect on armour penetration of firing cores of different
densities”, July 1947

An ARDE report on 20-pounder APDS penetration performance.

Property                       Imperial         SI
Core weight                    4.7 lbs          2.134 kg
Core diameter                  1.6 ins          40.64 mm
Round weight                   8.424 lbs        3.824 kg
Propelling charge weight       10 oz 12 drs     0.305 kg
Core density                                    14 g/cm3
Sub-projectile diameter        2.08 ins         52.83 mm
Muzzle velocity                4 650 ft/s       1 417 m/s

Penetration at 30º for core density 14:

Range (yds)             Range (m)             Penetration (mm)
    0                        0                   303
  500                      457                   287
1 000                      914                   271
1 500                    1 372                   255
2 000                    1 829                   240
2 500                    2 286                   225

Add or subtract 10mm per unit density between 13.0 and 15.5.

DEFE 15/709 “Theory of armour penetration by tungsten carbide shot
and the effect of headshape on performance at high velocities”, 1945

“In plate at least 8 calibres thick the actual resisting pressure
rises to this same maximum some four calibres from the front surface,
and maintains it until some two calibres from the back surface.”

The maximum referred to is the pressure at which penetration occurs
by punching a cylindrical plug, rather than ductile hole enlargement.

The following figures are taken from a graph by eye, and show the mean
resistive pressure of homogenous armour for different thickness/diameter
ratios:

t/d ratio             tons/sq. in.          megapascals
3                     202                   3 120
4                     220                   3 398
5                     234                   3 614
6                     247                   3 815
7                     258                   3 985
8                     267                   4 124

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All the best,

John.

[Whirlwind]

thanks for putting that up, John

[Author]

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