As far as I know, a Stevens 200 comes in a short action and a long action. The long action is the 270, 30-06, 7mm Magnum and 300 Magnum. The COAL for the last three is some where between 3.3 and 3.4 inches. If the magazine length is 3.5" then either you will have to single load a 7mm STW or seat the bullet deeper so the COAL is a little shorter than 3.5" to get it to feed in the magazine. I am not positive the action will be long enough to feed the 7mm STW or not. If it is not long enough, then you will have a difficult time unloading an unfired round. Measure from the bolt face in the fully open position to the front of the ejection port. If it is less than the COAL, it will not eject the unfired cartridge. The bullet will hang up and will not clear the ejection port. You will have to withdraw the bolt to get it out. I know this from experience, trying to run a bullet seated out very far in a short action rifle. I had to seat bullets in further than I wanted too.
Good Luck and Good Shooting