There is something you can check before sending it in, if you want.

First, put in an empty magazine and pull the slide back by hand. Did the slide lock back? If yes, it is possible that the problem can be eliminated by disassembling and cleaning the magazines (I use CRC silicone, and wipe dry), and carefully cleaning and lubing the gun per factory manual (not excessively).

Then test the gun with a full-power quality ammo (WWB tends to be a little wimpy). Just put in a couple of rounds at a time for the test.
If it then works, after shooting it a few more times it will probably shoot the WWB OK.
A combination of not clean, brand new, and wimpy ammo can cause short-stroking the slide and failure to lock.

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Science plus Art