Put about 150 rounds through my brand new G19 gen3 Sunday and noticed as I was cleaning it today this line going across the barrel where the slide is. Definitely wasn't there before I shot it. Is it already showing wear and tear with only 150 rounds in it?
Yup! That's where the finish on your barrel is wearing off from the slide moving across the top of your barrel hood. Completely normal.
Completely normal, and if I may add, the black finish is rather thin and is cosmetic, the anti rust properties of the finishing process glock uses is deeply ingrained into the barrel, so have no worries!
Yup! You can remove the black finish with a Q-tip and some Flitz. The nitration is in the metal, not the finish.
Looks normal to me. Just keep shooting it and don't worry about it. Glocks are not known for their good looks.
After 4+ months and around 1500-2000 rounds, that's still the only wear my G19 (4th gen) shows aside from the slide stop losing paint! My Ruger LC9 shows much more wear and has been used far less and is less than three months old...