The attached picture shows 4 x 20mm Hispano Rounds:
Armoured Piercing Mk 1z - with a sharp pointed tip.
Armoured Piercing experimental using a Madsen projectile with a brass ballistic cap.
Armoured Piercing Mk 2z with a Bakelite ballistic cap unpainted.
Armoured Piercing Mk 2z with a Bakelite ballistic cap painted white.
I recently obtained examples 1 and 2 from a retired employee of one of our research establishments. According to Peter Labbett’s and Freddy Mead’s ‘British 20mm Hispano Ammunition Technical Ammunition Guide’, the AP Mk 1z with the pointed tip was not accepted for service because it tended to break up in the barrel and had a poor armoured piecing performance.
The gentleman I got the two rounds from said that this was incorrect and the reason that the MK 1 was rejected was that the sharp pointed nose used to dig into the aluminium of the early circular 60 round magazines when the gun was fired and this caused it to jam. This sounds reasonable as the early Ball and HE versions of the rounds had flat tipped projectiles or fuzes. According to him, to overcome this problem Madsen AP projectiles were trialled with brass ballistic caps fitted. If you look closely you can see that the driving band on round 2 is slightly broader than the normal Hispano round. I have included pictures 3 & 4 to show the AP Mk 2z round which was accepted for service, the cap should normally be painted white, but it is clearer in the unpainted one.
I have never seen any reference material to support the explanation above, has anyone else?
Thanks in advance