noclue has the right idea here. It's all an abstraction. A character rolling Guns may have fired one shot or a dozen shots, but it's still one roll. A 'hit' (i.e. an attack roll stronger than the defense roll, causing stress) may not be a literal hit. It may be a shot that bounced off the armor, or passed right by your ear, or forced you to dodge by rolling on the ground. When a character is too stressed, they start taking consequences, but even those can be out of the ordinary. For example, against a steel-plate wearing opponent, the minor consequence "dinged up" might be appropriate, representing that they've been hit, their armor withstood it, but it might not continue to do so.
Also, don't think of the weapon rating as how much 'damage' the weapon does, nor the armor rating as how much 'damage' is prevented. Instead, look at it as threat and stress. A big honking two-handed sword (weapon 3) is going to worry and stress you out a lot more than a little dagger (weapon 1), but your chainmail suit (armor 2) does comfort you somewhat.