I have a simple (and probably silly) question regarding the lock that comes with the M&P. Is it okay to leave the slide locked back in order to use that barrel lock, or does leaving the slide back cause damaging tension on the slide lock? Thanks!

Locking the slide back does not harm the gun.

However, using that lock on a gun kept at the ready and urgently needed can cause death to the user.
On the other hand, if the intent is to store the gun, that lock is not adequate protection against unauthorized use, and the gun should be locked out of sight in a secure safe, IMHO.

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Science plus Art

Good points. The lock is kind of lame, isn't it?

That lock is a perfect symbol of irrelevancy.

People interested in accessing the firearm such as curious kids and felons, will be skilled enough with a lockpick to bypass that "lock" faster than Rob Leatham can clear an IDPA stage.

If a gun owner wishes to ensure the weapon isn't misused, they would be wise to first send any included locks to the bottom of the nearest dumpster or body of water ,and field strip their weapon before storage. It is somewhat difficult for a crook to shoot an M&P pistol sans barrel , and an AR15 or AK47 becomes rather useless without its bolt carrier assembly.

That's the kind of lock that comes with the gun. I guess I need a cheap gun safe.

Yep, I would never run that down a barrel. I've only used it a few times, and down the magwell it went.

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