What's the approximate serial # range for the preban receivers that were marked "7.62MM"

Don't know 'bout the 7.62mm, but circa 84,000 is September 1994.

-- Chuck

Thanks, I think I heard it was ~61,000-62,000 range.

From my article at m14.freeservers.com/about.html

Investment Cast Recievers - Armscorp, Federal Ordnance, Smith Enterprise, Springfield Armory, Inc. and other companies made receivers using an investment casting process. Around serial number 040000, Springfield Armory made some changes to the design of their M1A (TM) receiver. The chamber was moved very slightly forward to improve accuracy and increase bolt lock up time. Some Springfield Armory, Inc. receivers have a ridge on the bottom right hand side that may slightly interfere with the stock fit. This ridge has been identified on M1A (TM) rifles from serial number 000049 until somewhere between 034XXX and 043XXX. This bottom side ridge was removed from the design as part of the changes made. At some point, they also changed their receiver design to machine a small hemisphere on the right rear sight ear outboard side for use of a ball detent with a match windage knob. Springfield Armory, Inc. used to include "7.62-mm" as part of the receiver marking. This marking has been identified on M1A (TM) rifles from serial number 000049 until a serial number somewhere between 0584XX and 063112. The "7.62-mm" marking was dropped because Springfield Armory, Inc. began making the M1A (TM) in different calibers. Federal Ordnance made two types of M14 receivers, one for all USGI parts and one for all Chinese parts. USGI parts were used extensively in Federal Ordnance rifles through at least S/N 0088XX.

Exactly what I was looking for.... THANK YOU!