I hope this isn't too stupid a question, but I don't have nearly the experience of most of the members on here.  I just picked up a Bushmaster A2 upper assembly (upper receiver, barrel, no BCG), one piece upper with built in carry handle and 16" barrel.  The barrel is marked on the bottom (not on top forward of the A2 sight post as I would normally expect) and marked "BFI 5.56 Nato 1/9."  I know more recent production barrels are marked with "BMC" or similar and marked on top (as was the one that came with my BM carbine, the lower of which I want to attached to the new upper).  So the question is, is this normal for BM at the time this upper was probably manufactured?  Really dumb question:  Is this barrel really "upside down" and is there anything potentially harmful in shooting it, if that's the case.  Sorry, just bear with me...

I have, or have had, 4 Bushmasters purchased between 2003 and about 2009.  I have never seen one marked on the bottom, but I think someone simply put your barrel in the rollmark machine the wrong way.  It doesn't affect anything.

As an assembly, there is no way for it to be assembled upside down.  In order to do that, the alignment pin would have to be sheared, or the barrel would have to be completely loose on the barrel extension.  If the alignment pin was sheared, your feed ramps would be on top and your and your front sight base would be on the bottom.

Yeah, other than the roll mark on the barrel, everything else appears normal.  I always assumed the rollmark would be put on the barrel before the barrel was installed on the receiver, etc, but in this case it appears that the assembled unit being put in the rollmark machine may be what happened:  the rollmark on the barrel is perfectly centered the way you'd expect it to be, except that it's on the underside of the barrel rather than on top, as it the whole assembly was put in the rollmark machine upside down.
One thing that made me question this is that I read somewhere that Colt up until the early- to mid-70s marked barrels on the bottom, so I thought this was an early attempt by BM to emulate Colt that they abandoned in a short time.
Any other thoughts from anyone?

I bought my E2S in Dec 2000.  The marks are on the top of the barrel.
B MP 5.56 NATO 1/9 H BAR