Wenig New American DIY trap stock for Beretta 12ga autoloaders. Right hand. This one was specifically made for a 390, but will fit or can be made to fit with minor modification AL1, AL2, AL3, 300, 301, 302, 303, 390, 391, 3901, A300, and A400, as well as the Browning B80. I wet the stock down with iso alcohol to show grain, it's fairly plain but has decent color, beyond that the stock is unfinished and as it came from Wenig. There's a bit of discoloration on the comb from where a stick-on cheek piece was, but I'm sure this will come out when the stock is sanded and finished. It measures 12.5" from center of inlet to center of butt, best guesstimate I could give would be a 14 3/8-14 5/8ish LOP w/ a 1" pad Most current pricing I can find from Wenig would be $315+ship. This one is yours for $265 shipped.
Just to clarify a bit on your description, it will probably only fit the alloy receiver B80. The steel receiver stock is a different animal.