Why is a Black powder gun considered Primitive? Sure the loading, firing and manufacturing methods are primitive compared to post American Civil War guns, but that doesn't mean they're not effective. Some muzzle loaders had a .50 Cal. ammo and/or could shoot Shot and are still used for hunting big game today.
It's one point weaker than a Autogun as far as dice rolls, but with the Primitive Feature it's effectively half of that against anyone wearing none Primitive armor.