Live fire trials against Strv 103 (1971)

In 1971 live fire trials were carried out against the engine hatches of the Strv 103 with the goal of determining the critical velocity where the incoming projectile will penetrate the armor 50% of the time. The tests were carried out using a 105 mm L/62 barrel using the Slpprj m/66 round (Swedish designation for the British L52A1 APDS).

The rig used in the test.

In total 4 hatches were used in the tests all of which were sourced from production version Strv 103’s. Measurements were taken in the corners of each hatch and the angle of the armor was also measured before firing.
After firing pictures were taken of the effect of each round.

Measurements of the engine hatch thickness

In total 10 rounds of Slpprj m/66 were fired with increasing powder charges to simulate different ranges/velocities between 1199-1355 m/s. Out of these 4 rounds penetrated the engine hatch, one round shattered before impact and five rounds failed to penetrate the armor. Out of the penetrating rounds 3 had a impact velocity of 1318 m/s and above and one had an impact velocity of 1268 m/s. The latter was however disregarded since the shot managed to impact a oil filler port, and because another round with an impact velocity of 1267 m/s failed to penetrate the armor when not impacting the oil filler port.

This chart notes the following
Round number, Hatch used, temperature of the hatch, impact velocity, impact angle, ? angle, weight of the powdercharge, which rib was impacted , width of the impact, length of impact, depth of impact (G means penetration), deformation of the engine hatch and finally notes.

By taking the two impact velocities where the round did not penetrate that were closest to the two impact velocities which did penetrate (all of which were within the range of 20 m/s from eachother) the critical speed was able to be calculated as the average of the velocity of round 67 (1308 m/s) and round 68 (1318 m/s).
The report found that the critical velocity for the Slpprj m/66 was 1313 m/s. Its important to keep in mind that this was for an angle of 12,2-12,3 degrees and that this value only applies to the ribbed armor of the Strv 103 Engine hatches.