for the only pistol I have ever had to warranty (and not a glock) I contacted the warranty support phone number at the manufacturer and they happily gave me a prepaid Fed EX label. I boxed the gun up, stuck their label on it, dropped it off at fed ex. No one asked me what was in the box and I never said. about a little over a week later, fed ex was back at my door with an ID and Signature required package that was my fixed pistol (my state allows for this, not all do).
My local FFLs want about $80 to $100 total to pack and ship a pistol, screw that, it is way too much for a warranty claim
You can also try this service (works with FFLs)
www.shipmygun.com
Had I not got a free shipping label, I would have used this. The total cost estimate I got was $32
contact the manufacturer first, see what they are willing to do.
I would have even been happy to pay for the manufacturer to create me a shipping label where I am only paying their discounted cost of shipping (but they just gave me a prepaid label and it worked out, I got the label in an email while I was still on the phone with them)