I’ve just managed to get some new examples and found three that seem to have blackened bullets. I don’t know if this is due to corrosion (it looks too uniformed or that it has some specific meaning.
These aren’t black tipped AP.
The headstamps are:
y n 3-74
T Z 79
T Z 80
They all have Y stamped on the primers and all are non magnetic projectiles.
Are these just standard Ball rounds or dose the black signify something?
I can post pics if need-be.