Copied this from my post over at Koolaidtalk as guys over here tend to actually shoot, rather than just wax poetic on how great Glocks are, so I'm betting I'll get better feedback/discussion from you guys...

Got an "02" recoil assembly the other day and got to hit a range yesterday to check it out...

I have a Gen4 G17 and with the recoil assembly that came with it it's seen over 2500rds and has had exactly 3 stovepipes over that round count, 2 of which came from the same batch of known to be soft shooting and inconsistent UMC from wallymart , I'm pretty sure the malfs can be blamed on the combination of shooting cheap wallymart fmj AND the fact that the new recoil assemblies in the Gen4 G17's are on the stiff side for a 9mm.
That said, with the original spring: the gun does shoot really flat (flatter than a Gen3 with a ISMI 15lb spring on an OEM rod), the sight tracking is awesome shot-to-shot, has very little felt recoil, and it has softened up quite a bit compared to when new.

I called and asked for the new softer "02" spring as I want the gun to function as best it can, and in the past over thousands and thousands of rounds I've always run my 3rdGen G17's with ISMI 13's or 15's and found them to run better than with the 17lb stocker that way, so I was looking for the same effect in the Gen4.

Upon install it indeed felt lighter, but not really by much, or nearly as much as I expected it would.

Well, ran 200rds through it yesterday and gotta say I'm kind of disappointed... the effects I was expecting from running a slightly softer spring didn't materialize, quite the opposite actually.

Felt recoil was greater, muzzle flip was increased, and sight tracking was kind of all over the place... WTF? and, I got hit in the forehead with brass on quite a few occasions so it's ejection pattern wasn't any better either, which is not a good sign as a properly sprung gun will throw brass consistently and make a nice neat pile of brass to your right. Also, my trigger that was stellar before the spring switch got noticeably worse with the "02" in the gun as for some reason the lock-up of the gun isn't as tight when at rest with the "02" installed (guess it has something to do with the fact that it's a progressive design were it reacts different at rest then when under recoil).
Yeah, no malfs, but I'm not one of the guys complaining of reliability issues, I think the spring assembly in the new Gen4 is indeed too stiff if someone is expecting it to react just as a 3rdGen G17 would, but since it shoots flatter, softer, and has much better lock-up then the 3rdGen guns, I understand something had to give since you can't get something for nothing, and can live with it as long as the issues are confined to the new guns only being less tolerant of underpowered ammo or a little more sensitive to limp-wristing which is in reality where I feel most of the malfunctions being reported are coming from with the Gen4's.

I reinstalled the original spring as it doesn't take all day to recognize sunshine as they say, no need to waste any more rounds to find out what I already knew (and I brought 500 to the range with me but the "02" was a total bum out so I hung it up after shooting just 200), trigger went back to being awesome and all was well. 200 isn't a lot, I know, I would've shot all 500 and another 1000 if I thought it was worth it, it just wasn't, the difference was obvious, and it sucked.

While the original spring is stiffer, it's strange, there isn't that big of a difference in the feel between racking them back-to-back so much, but the lock-up or rather the initial bit of strength it takes to unlock the original spring from battery is noticeably greater...
While I'm no firearms engineer, I don't think modifying the original spring is going to do it, and don't think this is what the Gen4 G17 owners out there were looking for, these dual-springs are progressive and they work in-tandem with themselves in concert with all their components together as a whole... I think Glock needs to design and manufacture an entirely new spring top to bottom, different rate for the little inner spring, different rate for the outer spring, not just cut down the ones they've been putting in the Gen4 22's and 17's, doesn't feel right and don't think this is the end of it.

Full disclosure, the 02 spring I got looks like it's a pre-production one, the end coils look rough, showing evidence they were ground down from possibly a clipped 01 Gen4 assembly... maybe the production ones will be different (I sure hope so), time will tell I guess.

If anyone else could post their experiences with the "02" springs for the Gen4 here it'd be helpful... hope other guys experiences turn out more promising then mine.