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Max. Perforation with a Given Gun System

With a real gun/ammunition system the target velocity optimization is of secondary importance. A well chosen combination of penetrator length and diameter is relevant. The 120mm smooth bore L44 gun is a good example for showing this. On the basis of „120mm Tungsten Penetrator Design“ – see under downloads – the accelerated masses and the corresponding muzzle velocities were calculated for a lot of feasible penetrator geometries. The perforation equation provided the perforation lengths at a single plate target with a hardness of BHN235 under an obliquity of 60°. The diameter along the penetrator length was supposed as shown in the following graph.

The upper frustum has a diameter of 7mm and the cone angle is 9°. The propellant mass is dependent on the projectile length:
700mm -> 8.9 kg and 900mm -> 8.1 kg (linear interpolation for other penetrator lengths)

The following graph shows the perforation results at the muzzle.



red lines
 penetrator length (tungsten)
from 650 to 850 mm with step 50 mm
blue lines
 penetrator diameter in the sabot part
from 20 to 34 mm with step 2 mm
green lines
 aspect ratios L / D
from 24 to 36 with step 2
The perforation calculation for a penetrator with a length of 800 mm and a diameter of 26 mm you find "here".
Long and thin penetrators perform best. For all ratio of L over D the optimum velocity is within the wide range of 1300 to 1500 m/s. In the caliber 120 mm penetrator with lengths greater then 850 mm are not feasible. For best perforation you have to make the 850 mm penetrator as thin as possible. I think that L over D of 36 (D = 23.6 mm) is the maximum possible value. The findings are only valid at muzzle. If you consider real combat ranges such as 2 km then it looks quite different as you see in the following graph.

The optimum velocity is now in the region of 1500 to 1650 m/s. The best length is reduced to 750-800 mm.

The following graph shows the perforations of penetrators with L over D equal 32, different lengths and ranges from muzzle to 3 km. If we don’t include the perforation at muzzle then a penetrator length of 700 mm gives the best overall performance.

 

 
 
   
   © April 2022 by Willi Odermatt