I have a Model 1897 pump, a Model 12 pump, and a 93/97 IAC pump. You can stuff 5 rounds in them, pin the trigger back and start cycling the action fast. All the rounds will "slamfire". And they will fire as fast as you can work the action.
This does not apply to S X S.
Drop a couple of live rounds in a S X S. Start closing the action. Remember the firing pins will protude momentarily maybe an 1/8th of an inch when the trigger is pulled. If the S X S fires and the action is not locked, nothing exciting will happen. Sometime back a few cowboys removed the locking mechanism and simply held them closed when fired. Ain't dangerous at all. Again, if it WILL fire, the thing is so close to closed, nothing will happen. Being so colse to closed, the hull will maiintain and the force of the shell firing will b no different if you hd the action closed.
Co-incidentally, I happen to be working on a Stevens 311. I have chopped the barrels to 20", lengthened the forcing cones, lightened the hammer springs,andpolished some stuff. I removed the small rib that goes over the locking mechanism. I removed a bunch of metal from the locking lug. Now it is a slim bar with a rounded point. Chamfered the barrels and polished the heck out of the chambers.
As far as the action staying open, I believe I may have found cure. BTW, the "fix" for the Stevens is not for all the Stevens. The gun cocks on opening. The point where it is cocked is about 2/3 of the way of opening the barrels. I believe I can get the action to cock at the last inch or to of opening thereby relieving tension and it will stay open. I'll report back.