A rifle chambered for 243 WSSM will not fit in your stock. It's a super short action and not a short action. Also, when dealing with Winchester's it is necessary to know if the stock fits a pre-64 action, post 64 push feed style action, or a classic action. The pre-64 was made from roughly 1936-1964. The post 64 was late 1964-1993 or 94. Once you know what generation it fits the stock should work with any short action Featherweight. The standardshort action is designed for cartridges such as, 22-250, 243, 7MM-08, 308, & 358. At one time or another the Featherweight has been chambered for the above mentioned cartridges. The Featherweight has one item to note the barrel contour on the Featherweight is different than the contour on the standard short action sporter models. If you choose to buy a standard contour barrel any competent gunsmith should be able to relieve the barrel channel in your stock to fit the barrel contour of your barreled action. However, they won't be able to change the stock much in the area where the action fits.