It probably aint a preban,If it is buy It right away...Most preban stripped AR lowers are going for around 700 to a thousand!!
If its a post ban thats still a pretty good price,prices lately have been around 130-175..
Bushmaster may have a serial number listing at their web site,if not give'em a call..
To be assembled as a preban rifle it has to have been shipped from the factory as a complete weapons before the ban....
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Follow the white rabbit...