Welcome wingnuut! developed by Marlin to compete with the Winchester Big Bore series, just over 16000 produced, from 1980-1983, in the hard hitting .375 winchester cartridge,
it launches a 200 grn jacketed flat point @2400 fps or a 220 grn @2150 fps, a real thumper, filling the niche between the 30-30 & 45-70.
It was not very successful by sales standards, but has a sort of small cult following, and is a handloading deal, as ammo is only produced by Winchester in limited runs.
I have one and "love it" !! and yes it is a 336 frame. Any others feel free to chime in! Hang on to it as it will increase in value!! or I can take it off your hands! he he he!