Thin it 50/50
It you want a high gloss finish do a top coat of 1/3 mineral spirits 1/3 BLO, and 1/3 oil based polyurethane.
I guess the MD law would make these illegal.
http://www.berettausa.com/shop-by-department/firearms/rifles-and-carbines/tactical/
I think they might have had some plans for the ARX-160 in 5.56 too.