20x110 questions


#1

1 & 2 in the pic 20mm Oerlikon, #3,4 & 5 20 US Navy. The rest are? I think the last one is Oerlikon also.


#2

Last FOUR are Oerlikon 20x110…the first Three are Fired (expanded neck) and the last Unfired.
The expansion is due to the “anticipated Firing” cycle of the Blowback-Recoil Oerlikon mechanism ( Firing pin falls as the cartridge is still chambering, but before reaching battery ( Bolt head is already within chamber);This allows for a light breechblock, and no “locking” mechanism. Hench the rebated rim-case, which can sit in a case-body -diameter Bolt, which enters the entire chamber.

Hispano-Suiza Guns use a normal rimless case, as the cases headspace on the shoulder, and the bolt has a positive “locking wedge” when in battery…Recoil aids extraction, and a gas-bleed unlocks the Wedge.
Regards,
Doc AV
AV Ballistics Technical Services


#3

THANKS DOC!


#4

Nos. 3,4,5 and 6 all look like 20x110 Hispano to me. Although they were used by the USN more than the USAAF/USAF (especially in the decade after WW2), I wouldn’t describe them as 20mm USN as that might cause confusion with the 20x110 MK100 series of the 1950s and 1960s, which were USN/export only and used a wider case (a slightly lengthened 20x102 Vulcan case).


#5

Thanks Tony!