Most modern semi autos lock back on an empty mag and the slide wont release unless you either pop in a fresh mag with ammunition, or take the mag out and release the slide. Does this happen with the extended mag with ammunition in it? Since the gun is meant to lock bag on empty mags it makes sense that the slide wont release with an empty mag in it. Also I would be careful with all that filing your doing, too much and the gun will stop locking back on an empty mag since you took off too much material. I don't understand why you didn't call Smith & Wesson first.
Edit: Just watched the end of the video. You know when the slide released all on its own without you touching anything on the gun, well it looks like you filed off too much metal and screwed up the slide lock on that gun. I would send it back to Smith & Wesson and hope they cover the cost to repair it.
Last edited by Dragline45; October 20, 2012 at 09:32 PM.