That looks like CMP walnut maybe? Get some pure Tung oil and hand rub it in. Hit it with some steel wool or scotch brite pad in between coats. You'll not only protect the wood, but it'll bring out the grain and give it a nice luster (not as shiny as varnish or lacquer though). It was also the prescribed finished by Uncle Sam among others so it's in keeping with the history. I put about 5 coats on mine and couldn't be happier with how it turned out.
DSA Imbel FAL 21"
Mossberg 590A1 20" w/ ghost ring sights
Sig Sauer P226r Two Tone
CZ455FS Mannlicher w/ Leupold VX-1 2-7x28mm
Ruger Mark III Hunter w/ Ultra Dot and Volquartsen adjustable trigger
Colt M4 LE6920
WTB: Gen4 G19, Sig P210, S&W Model 41