US 20MM 'Transitional' M99

[kahu1]

I think this is what this is!.
See pic,middle projectile, for comparison with M90 series(M99A1), M99 (?) and M50 series(M56) projectiles.



This one i got as a 'stuffer',in a US Hispano(M21A1) case, the only markings i can find on the damaged driving band are; -7-45-20MM M .
This is shorter and different profile to the standard WW2 vintage M99 practice projectile,being closer to the M50 series projectile of the 1950s-.
My understanding is these projectiles were used with the development of the .60/20mm (20x103mm/M50)T61E1 case type from the original .60cal round in the late 1940s.
Any info appreciated!.
Bob

 

[orpheus72]

Hi Bob,

I got a similar projectile like yours in it's original casing.

I was told the projectile was a 'reworked' M99 projectile (as used in the 20x110) and it indeed was from the .60/20 developments tests

 

[SG500]

Nice rounds guys, I've always been interested in the early developments of the .60 cal rounds.

The attached photos show from left to right:

20 x 110
Headstamp FA51
Driving band stamping PMM-1-4-51 20MM T-114

20 X 102
Headstamp * FA * 52
Driving band stamping PMC 4-2 52 20MMT-69E1

20 X 102
Headstamp *FA*48
Driving band stamping AGS-47-45-20MM-M99
White stencilling FA-E-816 T61E1

20 X 102
Headstamp LG 52
Driving band stamping *HMC-1-7 52 20MM T61E4*
White stencilling T-154


All INERT.

Dave.

 

[Tony Williams]

Sorry to revive such an ancient thread, but I found this when researching US experimental aircraft guns and ammo in the post-WW2 period. I've been ploughing through Chinn Vols III and V and discovered that the T61E1 TP projectile shown in this thread was also used in the ammunition for the Armour Research Foundation T33E3 gun (modelled on the Rheinmetall-Borsig MK 103), in a case designated T7. Earlier T33 models used the huge T5 case (20 x 158RB) which fired a 130 g projectile at around 1,150 m/s, but the E3 was a smaller and lighter gun using ammunition with a smaller case than the T5.

I'm trying to track down this mysterious T7 case. While smaller than the T5, it was still a lot bigger than other US 20mm cases like the ones for the 20 x 102 and 20 x 110 USN: the T7 contained 58.3 g of propellant, almost as much as the T5 and far more than the 30-40 g of the 20x102 and 20x110 rounds. Chinn provides a clue in that he says the T7 was for a round developed for the T74 cannon - which was the US designation for the Mauser MG213C revolver cannon which ARF was carefully studying. This used a 20 x 135 case of about the right capacity, and fired the 104 g T61E1 proj at 1,150 m/s, which is also about right.

So, I have tentatively tagged the T7 case as being the 20 x 135 from the Mauser MG213/20. If is isn't that, then the T7 must be something else that I've never heard of!

Comments anyone?