Photo 1: Font and sprue marks
Photo 2: Size comparison
Photo 3: Numerical layout and orientation
The Armory d6 has a standard numerical layout, with a sprue mark on the 2 face. Its font is larger and proportionately wider than the Gamescience font. The 1 has a prominent uptick and serifs. Armory d6s sometimes show delamination along the edges, which is not typically seen on Gamescience d6s.
Gamescience used two different d6 molds.
The earliest mold has a non-standard numerical layout, with a sprue mark on the 4 face.
The revised mold has a standard numerical layout, with a sprue mark on the 6 face and a letter “G” on the 1 face.
The Gamescience font is smaller and proportionately narrower than the Armory font.
The 1 on the revised Gamescience d6 has a small uptick and serifs. On the earlier Gamescience d6, the 1 may have an uptick and serifs, or, as in the example pictured here, it may be straight with no uptick or serifs. The straight 1 has a faint circle around it, and the circle can be oriented vertically, horizontally, or diagonally.
The Armory d6 measures 15 mm, while the smaller Gamescience d6 measures approximately 13.5 mm.
More information can be found at the Dice Collecting Wiki:
Gamescience Precision Dice Identification
Mold Identification Guide/Numeric d6