Purchased a DSC 20 inch complete upper from a friend, he stated he purchased at a lgs(local gun show some years ago complete from J and T ). Upon inspection I noticed that the fsb is marked b1, and no f , the upper receiver is marked m4, the detachable carry handle is marked with a rectangular box . In comparison to my other 20 inch upper, which is marked with a f fsb, not marked as a m4 upper and has the rectangular box carry handle, what difference should I expect to see in my range results. The DSC is different at 100 yards with the same ammo, and setup. Thanks.