I had a G17 that shot 8” left at 20 yds. I had plenty of other Glocks in my safe and never had the issue before. A couple other people shot it with the same results, so I began experimenting with different parts to correct it. I quickly discovered that is was in the upper, as swapping other uppers onto the G17 frame resulted in perfect hits. It got weird when I swapped barrels and slides. The slide worked great with other barrels, and the barrel worked great with other slides, but putting the two together, on any frame, resulted in the way left hits. Ultimately I didn’t want to spend any more money on replacing either part so I gave up on it and sold it to a buddy who drifted the sights to correct, but it looks terrible. Very weird that the factory parts didn’t like each other.