My moderately large pile of steel just arrived from Chicago (Admiral Steel). It’s amazing how little space 600 pounds of steel takes, this is a stack of 2′ x 4′ sheets of various thicknesses ranging from 14 Ga (0.80″ / 2mm) down to 22 ga (0.032″ / 0.8mm). Interestingly the (nominally) 20 Ga sheets which are supposed to be 0.040″ (1mm) thick came in at a hair over that thickness, so I have a lot of material (20 2′ x 4′ sheets) that is very close to this thickness. Fortunately, this is the range of thickness that most medieval armour sits in (breastplates, helmets and gorgets are thicker, some gauntlet components are thinner) so I anticipate that I will go through this in a year or three.
The whole stack is about 2″ thick, with the thicker material in the back since it gets used less. I’m currently working on some gauntlets, so I’ll try these in the 1 mm thickness first (so that I have material that I can lose to abrasives when I “clean up” my hammer scuffs) and I will then test the medieval thickness which is generally on the order of 0.030″ (0.75mm) and see if it makes a significant difference in how it moves – gauntlets made of 16 Ga (1.5mm) material are very “clunky” because the plates are thick enough that the “stepping” for articulations is noticable: this is mostly alleviated in 20 Ga material (1mm) but may be even better with the “correct” thickness used.