I wouldn't worry about it unless it's relevant. Having an opponent with an archaic weapon can give you an opportunity to do maneuvers like "He's reloading" and use that on your next attack, saying that you are waiting with your approach until he is reloading, and since his weapon takes a lot longer than modern weapons, he can cross the distance and get to him. You could even do a guns vs. athletics roll to see if the guy finishes reloading first, if you like.
But I wouldn't put down any rules like "it takes X exchanges to reload" or something like that. It doesn't feel like it would accomplish much, other than punishing a player for his choice of style.
Maybe with some sort of benefit attached to it. Making the reloading a maneuver in itself, and the weapon has a stunt that gives you +3 for tagging that aspect on your roll (or +4 when only using it as additional damage). You'd still need to do it, but it would give you a benefit beyond what would usually happen.