I believe on all of the MX series guns, the label on both sides of the guns is incorrect. It's labeled on the gun that it uses 6.5 x 38mm bullets, but I believe it should be 6.5 x 39mm. When hovering over those weapons in the inventory though, it is correctly written that it uses 6.5 x 39mm bullets..

Those are the mistakes I have found in regards to the incorrect bullet labels, but I'd review any other guns and their inventory descriptions to make sure they are consistent. {F18408} {F18409}