Apart from the overall size and weight of the weapon, another set of problems which may or may not be explored involves the ergonomics of gripping or controlling the weapon.
A greatsword grip long enough for two human hands might be too short for a giant to fit more than one hand onto, while a one-handed human sword grip might be too short for the same giant to properly grip at all. By the same token, a giant’s one-handed knife might have a grip that’s long enough for two human hands, but also thicker than a human sword grip so that it’s awkward for a human to hold, and perhaps too fat for a smaller creature like a halfling to even wrap their fingers around. A giant could find the grip of a human greatsword to be thinner than ideal, and while it would not prevent them from holding it as would a grip that was too fat, it might tend to rattle around more inside their grasp.
Similar issues might apply to guns, such as if a human takes a pistol designed for a gnome and finds that their finger can’t even fit inside the trigger guard.
