After WWI Colt maintained the rights to produce the Browning Automatic Rifle as a commercial venture; however Winchester sold some commercial BARs with exquisite finish on both the metal and wood.  

This MAY be a commercial Winchester trigger group.  It has the finest polish on the metal of any Winchester I’ve encountered and all the small parts are in the white Nickel Steel that Winchester was known for.  The trigger (marked W), change lever (marked W) and mag release button are shiny.  The sear carrier (marked W and M.S.) is also in the white.  The ejector is a Colt piece and the sear and sear spring have been swapped with a M1918a2 sear.  This is how it came.  If you buy this for a rifle with an A2 buffet it will fire in slow and fast; if you use this for a M1918 you will have to swap in a M1918 sear or have the sear trio ground off

a genuine mystery part