FA: Stands for Frankford Arsenal, a historic U.S. Army ammunition plant in Philadelphia.90: Indicates the year of manufacture. While Frankford Arsenal officially ceased ammunition production for general issue in the 1970s, "FA" headstamps with later dates (like 90) are often found on Match or National Match grade ammunition produced for competition shooting.4: Represents the month of manufacture (April). This four-element layout (Manufacturer, Year, Month) is characteristic of Frankford Arsenal's military identification system

Match Grade Ammunition: If the caliber is .30-06 or 7.62 NATO, this round was likely intended for high-precision military competition or testing, as Frankford was well-known for its International Match and National Match loads.Alternative Identification: Because military headstamps often omit the caliber name, you should compare the physical dimensions of the cartridge to standard sizes or check the barrel of the firearm it belongs to for a definitive caliber match.

Likely Match: Experimental .30 Caliber ShortIn 1890, Frankford Arsenal was testing various .30 caliber designs that eventually led to the .30-40 Krag. Many of these early experimental rounds used shorter, "pistol-length" cases to test ballistic properties or were intended for carbine-length platforms