I just cleaned my M&P 9mm Shield, but I was unable to get the slide to lock back. Saw a suggestion online to insert the magazine and eject a few rounds. I pulled the slide back once, and the gun was loaded. I pulled the slide back and ejected the first round. When I pulled it back again, it stuck. I can move the slide back slightly, but that's all. I cannot remove the magazine. Can anyone tell me how to fix this?

Make sure safety is on and keep pointed in safe direction.

Remove the baseplate on the magazine and get the rounds out. This should make it easier to get the magazine out.

If you can, pull the slide back far enough to remove the rear cover plate and then remove the striker. This should make the firearm safe.

If you have a round stuck in the chamber, you may have to use a good amount of force to clear it. However, if you remove the striker then you will be able to take the slide off the frame with the round still in the chamber.

Exactly where is the slide stuck? Is it stuck nearly in battery or near the slide lock? If back by the lock, then the nose of the round may be hanging on the ramp and trapped by the feed lips of the mag.

As BTJHP (sorry for shortening your handle), removing the floor plate will not only remove any remaining rounds but take the spring pressure off the slide. If the slide is back far enough, you may even get the partially chambered round to drop.

In any case, make sure it always points in a safe direction. Next time use an EMPTY mag.

A picture would help.

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Okay, I got the magazine and all cartridges out. The problem I was trying to fix was that I was unable to lock the slide back after cleaning and reassembling the weapon. I think the recoil spring must not have been aligned as well as I thought, but now I am unable to get the slide off. Can you tell me how to fix that? Thanks very much for your help!

Try putting an empty mag in and rack the slide really hard, making sure your thumb isn't interfering with the slide stop lever. If you still can't get it, try pushing the muzzle (right under the front sight) of the slide against a shelf.