The slide not locking back after the last round is, indeed, a common problem on many pistols -- not just SD's.

Here are the most likely causes:

1. The inside of the magazine is dirty, with gunk or dirt preventing the follower to move upward fast or firmly enough. Solution: Take floor plate off magazine, remove spring and follower, clean the inside of the tube and clean the spring (especially the sides which contact the magazine tube). Oil the inside of the tube very lightly, so as to avoid trapping more dust or dirt.

2. The magazine spring is no longer strong enough to get push the follower up fast enough to push the slide stop lever up fast enough to catch the notch in the side of the slide. Solution: Replace magazine spring.

3. The follower is damaged or worn -- the little ledge has been scraped or hammered to a lower level (its only plastic). Solution: Replace magazine follower.

Problems 1-3 can be eliminated as the cause if changing to a new magazine doesn't solve the problem.

4. The metal tab on the slide stop lever assembly, which interacts with the little ledge on the magazine follower, has been bent upward. If the tab is bent upwards too much, it cannot move the slide stop lever upwards enough to engage the slide in the rearward position. The tab may work intermittently, or work better with some mags than with others. Solution: a. bend the small tab back down to about 10 degrees below horizontal (you may have to take the slide stop lever out of the pistol to do this, then re-install it). Or, b. just install a new slide stop lever assembly.

5. Far less likely, but still possible: The inlet cut on the slide, for the slide stop lever, may have worn its edge smooth and no longer be able to catch the slide stop level assembly. Solution: it may be possible to use a small file to re-cut that ledge or notch in the slide at a right angle.

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S&W Rover