I have a Gen 3 17, a Gen 4 19, and a Gen 4 34. No issues with any of them. The Gen 4's have changeable back straps to fit different hand sizes, and a better (in my opinion) grip texture. The mag release is larger on Gen4's and can be reversed for left handed folks. I also like the recoil spring assembly on the Gen 4's. They seem to have less muzzle rise on recoil. If I purchase anymore Glocks they will all be Gen 4's.
There have been complaints from some Gen 4 and recent Gen 3 purchasers who are having weak or erratic ejection issues, with some of the brass ejecting back toward the shooter's head.
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