This one is right out of my line of knowledge - I purchased a cartridge in an auction - listed as a " 20mm Rock Gun Auxiliary cartridge for French Bazooka" .

The dimension are as follows ( in metrics ) rim 22.0mm ; head 20.048mm ; caselength 27.03mm ; Driving band at base of blt 20.55mm ; OAL 83mm.

The cartridge has no h/s , an electric primer , and a solid brass machined projectile with truncated nose .

A retired NZ Army Ammotech suggested these were in store but obsolete in the NZ Army in the mid 1960's , but he wasnt aware of the details at all .

I can supply a scan on request if wanted - havent figured out how to post a picture on here yet .

This is one of a range of similar cartridges (case lengths run down to 22mm) developed as sub-calibre training devices for rocket launchers - it was much cheaper to shoot these than the rockets!

The 20x27R was developed in Belgium.

Tony Williams: Military gun and ammunition website and Discussion forum

Thanks Tony

Do you have any data or even a manufacturing date for this item ?

Not a lot. They were developed between 1950 and 1960, but that's all I know.

Tony Williams: Military gun and ammunition website and Discussion forum