As TR indicated in this post: (May have to copy / paste if its not hot)
At some time in the past Armalite/Eagle Arms changed the way they made their bolt carrier.+
They went from an unshrouded to a shrouded bolt carrier.
The Eagle Arms rifle I have originaly came as a complete rifle.
I am trying to figure out at least about how old it is.
Would our Armalite rep be so kind as to ask around at the shop or in the office to see when Eagle Arms stopped delivering rifles with the UN-shrouded bolt carrier? ...about when?
Thank you sir.
If my memory serves me well it was around 2004 that the unshrouded SP-1 type carriers went away at Armalite.I know it was shortly after Armalite started using the 5.56 NATO chambers in all the standard barrels which was sometime around 2002.
If you call Armalite and give them the serial number they may be able to give you a more specific date of manufacture rather than trying to nail down the carrier change.