Slowshot:

If I recall the Cabela's photo correctly, this rifle was built on a large frame action such as those used for the .577-450 and .303 military and sporting rifles and the Greener single shot 12 gauge shotguns. I'm not going to say that no large frame was ever built with the straight cut rear receiver, but I've never seen one. The small frames had both types, with the Model 15 being the one with the straight cut and set up for a special peep sight. See the description of the various BSA small frame models with good photos at http://www.adamsguns.com/martini.htm.

Hope this helps.

Rem