I recently purchased my first AR-15, a Bushmaster X15-E2S with the A1 upper. However, I found out after the purchase that the lower was originally purchased separately from Bushmaster, with the upper being added later. How can I verify the upper is also a Bushmaster. I am pretty sure the barrel is, because it has the following on it:
B MP 5.56 NATO 1/9 H BAR
Thanks for the help.