N.Y. actually is N.V. -Nemzeti Vállalat (National Company)
(Bánya)gyutacsgyár means (Mine)Blasting Cap Factoy
The “NT” in the headstamp refers to the location of the factory (Nagytétény)
The company used to produce .22 RF cartridges till about mid 1970’s.
They had some special loads over the standar .22 Long Rifle and .22 Short rounds:
.22 Long Rifle with turned aluminum bullet for cattle killer rifles
.22 Long Rifle Centerfire
.22 Long Rifle BB - a strongly primed .22 LR case, no powder charge, with a single round lead ball - this load’s name was “6 mm-es szobatöltény” (indoor cartridge, or in German Zimmerpatrone)
.22 Short Centerfire BB - a strongly primed .22 Short centerfire case, no powder charge, with a single round lead ball
.22 nailgun cartridge (.22LR case filled with powder, covered with lackuered cardboard disc)
4,5 mm betétcsőtöltény (4,5 mm barrel insert cartridge) a rimmed centerfire-rimfire BB cap.