Are the last three digits of the receiver serial number etched in both barrel lugs? If so, both barrels were fitted at the factory.
If the serial number starts with "H", it's probably a .223 H&R Ultra Varmint.
If the SN starts with "N", I'd guess it's probably a .243 NEF Survivor.
The Ultra would have come with checkered laminated wood stocks.
The Survivor comes with a synthetic thumbhole (fisthole?) stock and flat bottomed synthetic forearm with storage compartments in both stocks.