Dummy 20mm round

  • There is a dummy 20 x 102 round marked on the inert projectile:
    20MM DUMMY
    My questions are:
    A) What is the meaning of “M51A2” mark ??? Is it the round index ???
    B) What other U.S. made rounds (not under 20mm) can be found today, I mean dummy (inert) rounds ??? I already know the old 20 x 110RB Oerlikon “S” rounds (with perforated and WW2 dated brass shell cases and soldered projectiles in place) and the 20 x 110 Hispano rounds with a bottom which can be unscrewed.
    Thanks in advance for any help, Liviu 08/10/12


The M51 was indeed the designation of the dummy version of the initial series of 20x102 ammo. It used the projectile of the M55 ball (practice) loading over an inert filler instead of propellant. Other loadings in the same series were the M53 API and the M56 HEI. At least some of the M50 series are still made by various manufacturers even though most of the major air forces have switched to more aerodynamic projectiles, like the USAF’s PGU-28.

I think that dummy or drill rounds exist of most if not all auto cannon rounds, to enable the safe testing of the weapon cycling action. Some are made just by using existing components like the M51, others are specially made with a special “projectile” which reaches down to the “primer”, still others are made with the “projectile” and “case” in one piece. I have a batch of various types and calibres in my collection and included a colour photo of a selection of them in the September 2009 issue of the ECRA Bulletin.