I have a Colt Sporter M4 Carbine lower without any engravings for a caliber.  Running serial number thru Colts website it was manufactured in 2011.  

Not like I'm tier 1 or an expert by any means, but this is first one(Colt) I've ran across that didn't have a cal listed.  I've been thinking about F1 this complete lower into a SBR, but if it is rare(which knowing my luck it's worth $200 at best), the last thing I want to do it F1 it and get aftermarket engraving done.

pic?

Right side of magwell is blank with no cal markings

well a google search of colt sporter m4 carbine shows no caliber so, NO.

The lack of a caliber may mean the lower was produced for sale as a lower, and not part of a complete rifle, or simply that Colt chose for that batch to mark the caliber(s) only on the barrels.

If you're truly worried about value, it might be worth a call to the Colt archivist for their $25 ("quickie") documentation letter as to its configuration on the day it left the factory, and possibly some more information about its lack of caliber markings. More in-depth complete letters are more expensive, like $100, as I understand it - but you might catch a break or I might be wrong.

Thank you, sounds about the line of what a gun nut buddy told me.  Just wanted to make sure.  Only thought there was a 1% chance of best I had a holy grail.