For any non-integer magazine values the magazine size is simply rounded to the nearest whole number. For example, a Dual DecurionDual Decurion modded with a max rank Magazine Extension will have a calculated magazine size of 32 × (1 + 60%) = 51.2, which will simply round to 51.
All arch-guns use their entire ammunition reserve as the magazine that regenerates over time, thus acting as both an increase in magazine capacity as well as maximum ammunition capacity.
Does not increase reload rate. Due to this, unlike magazine capacity mods for non-Archwing weapons, Magazine Extension does not increase sustained DPS.