12.7x99 Drill Cartridges

I see these Drill cartridges are listed as unknown in Ron Fuch’s lists.
Has the maker been identified yet?
They were used by the Australian Navy . Stainless steel.
The MA headstamp does not have red painted flutes. The AM cases have red flutes.

By the Dates on the headstamps,
MA was no longer used ( ceased once Lithgow became ADI-Thales,
MA is also found as a mark on US ordnance made in Milan, ?Tennesee?
I remember seeing prototype Drill rounds for .50 cal at Penrith Ammunition Base in West Sydney
During negotiations to buy a quantity of 7.62 and 5,56 Blank f 9i rfilm use…I think the stainless turned . 50s were there.
All commercially supplied…plastic, brass and steel.
Doc AV

Ron, thank you for sharing! Great reference!

And the first stainless steel dummies I recall having seen.