I got one of the pink dagger compact frames, so I got a P80 g19 slide.  It shoots. but just once, the slide doesn't come all the way back into full battery.  Any suggestions on what it may be?  Do I need a different guide rod with a lighter spring on it?  I put in an NDZ Performance G19 captured guide rod with an 18 lb spring.

Thanks

These are new parts right, not a used/worn recoil spring that you pulled from another gun or picked up somewhere?  You have the recoil rod assembly installed correctly right?  I know, it sounds stupid, but double check, it's easy to bump it out of its little notch when reassembling it if you're not paying attention.  When you have the slide assembly off how well does the barrel move in the slide and how is the lockup/hood fit?  Have you tried it with an OEM Glock or other recoil spring assembly?  Have you tried swapping slides and frames around to see if one is a problem child?    

If everything is in good condition and where it should be then I'd put a straight edge on your rails (because it's quick and easy to do and sometimes they get damaged or aren't in spec).  Does it do it if you cycle the action slowly by hand and when cycling it slowly with a dummy round in it?  If not then you should be able to feel where the problem starts and get an idea what's going on.  The trigger is resetting correctly?  The stock recoil spring for Gen 3s is 17#s (Gen 5s are 18#s)  and going up or down a pound shouldn't really make a difference in Glocks other than possibly in felt recoil unless you're using really fast or really slow ammo or have one of those lightweight slides such as the ones you see with a bunch of cuts to allow dirt and crud to get in the gun to make them aesthetically pleasing to people I've never met.  In my experience, Glocks tend to be more forgiving of user mods than a lot of other guns out there.


*Going up a bit if you're running hot ammo can help keep from beating up the gun and it can help slow the slide so that you're not outrunning your magazine spring; sometimes you need to increase mag spring weight as you occasionally see this when the slide is cycling too fast for the magazine spring (i.e. 10mm conversions in .45ACP guns, .45 Super, .460 Rolands, etc).  You may want to go down in recoil spring weight if you're shooting a lot of low velocity/pressure ammo, especially when suppressed.