I know that the G4 had some issues with ejection that was addressed.
That wasn't just a Gen4 issue. The issue existed in a small percentage
of recent production Gen3 and Gen4 9/40/357 models. For some people, simply replacing the extractor with a new one fixes it, for other people the new ejector is required. My Gen3 G27 had the issue, I used an extractor in it from my G23 which ejected fine, and it made very little difference. What fixed the issue was getting the new ejector for it.
The new ejector is now standard in Gen4's, but the Gen3's still use the old ejectors. In Gen4's that have the new ejector, it's incredibly uncommon to hear that they have the ejection issue now, and when they do replacing the extractor fixes it. The issue is still being reported in the newest Gen3's though.
The old ejectors are not defective in any way, and you don't need to upgrade to the newest version unless you experience the ejection problem. The new ejectors were made to change ejection enough to fix the erratic ejection issue.
If you get a Gen3 and it has the ejection issue, what you'll need to do is get the new ejector which can be found in the newest Gen4 trigger housings, remove that ejector from the Gen4 trigger housing and install it into your Gen3 trigger housing to use in your Gen3. If you still experience erratic ejection with the new ejector, that means the extractor is out-of-spec. Keep the new ejector in the gun and replace the extractor.
(So far only MidwayUSA and glockparts.com have been confirmed to have the Gen4 9mm trigger housing w/30274 ejector. No retailer has yet been confirmed to have the Gen4 .40 trigger housing w/28926 ejector.)
If you get a Gen4, make sure to get one that already has the new ejector in it. Put at least 100 rounds through it, and if you experience erratic ejection after 100 rounds, replace the extractor.
Let me know what you know...Reloads, lights, sights, ammo, etc. Thanks all.
Don't shoot reloads unless you made them yourself and are confident in their quality. Don't shoot unjacketed lead bullets through the factory barrel because it uses polygonal rifling. If you want to shoot unjacketed lead bullets, get an aftermarket barrel that has traditional rifling.
Some Gen3 .40 models experienced failures to feed with a light attached to the rail. The solution to this problem is either to remove the light from the rail, or to use stronger magazine springs. In some cases stronger magazine springs would not solve the issue, so you'd just have to remove the light from the rail. It's thought to be caused by the frame flexing less during recoil because the light is attached, and because the frame isn't absorbing as much energy by flexing, that energy is translated into faster slide velocity which is too fast for the stock magazine springs.
The failure to feed with light attached issue has not been reported even once in a Gen4 .40, the dual recoil spring assembly seems to keep slide velocity much more constant.
In my .40 Glocks I shoot American Eagle and Speer Lawman for range ammo and I've never had a problem with either.