The normal MAR fires gray and orange connectors joined by a green rod. Now if for some reason you prefer to shoot gray connectors you can use this instructable to make a modified magazine which will let your MAR fire gray connectors.
Note: This will not tell you how to make the whole gun. This only tells how to make a new mag so you can fire new ammo. If you haven't made the MAR yet then here is a link
More Instructables by me.