Originally Posted by spector56

i also have the same gun with the same problem glock27 gen4 upset about it to say the least 25 ftf out of 274 rounds slide is locking back every time and no my thumb is not hitting the slide lock lever called glock they told me to fill my mags to the max and leave them like that for about two weeks if thats a no go call them back guess at that point they will be getting it in the mail yes it sucks glad to see im not the only one good luck....

Assuming you're shooting factory ammo and the gun has all factory parts, your extractor may be out-of-spec. Some of the latest extractors are too large and don't move freely enough in the slide, this can cause failures to feed. I'd try replacing the extractor.

If you've never detail stripped a Glock before, you're better off just sending it back to Glock. Call them first and arrange it with them. You have to send it overnight UPS or Fedex, you can't send it through the USPS unless you have a Federal Firearms License. Ask them for a prepaid shipping label. They may not give you one, but it's worth asking.

An alternative would be a find a local Glock Armorer. It'd be much cheaper than shipping the gun back to Glock should you have to buy a shipping label.

Leaving the magazines loaded for a few weeks has no effect on feeding problems, the person you talked to doesn't know what they're talking about.