Installed my new 22 pound recoil spring (captured).  At first it would barely return if at all to full battery during function test.  Racked it several times until it would work flawlessly.  Went to the range yesterday and had several failure to feeds and non returns to full battery. Had to push the last millimeter or so to get to go in.  But after about fifty rounds it was getting better and better.  Eventually would cycle every round.

Anyone else had this problem after installing new recoil spring? 

What model did you test with?
Some have had issues with the aftermarket recoil springs in the G-20's trying to find the right one...
If I change to an aftermarket for my G-20SF, I will go with a non-captive setup for ease of changing out and I feel that it applies more force to maintain lock-up...but that's just me!  I run the Wolff 21lb non-captive setup with the Wolff recoil rod in my G-29 with no issues, also have other spring weights for other test. 

I have ISMI 22 pound spring.  on metal captive rod. it was a pain in the butt to put that spring on and screw the nut back on.  it was all kinda of wiggly looking when I was done.  now it looks true and straight.  I also but the heavy duty trigger spring and 6 pound firing pin spring in.

I also notice my shell casings all have a ding in them.  I guess from hitting the slide on ejection.  my glock is a first month production according to the serial number back in feb. of 1992 I think. been awhile since I looked it up.  I just wonder if they were built to withstand the underwood type ammo.  don't know what 10mm "hot" was back then.  the plastic "U" shape slide stop sure has taken a beating. Anyone use those rubber "gasket" things for the slide to protect the frame.  Just hate to spend 10 bucks on something that is most likely a gimmick.

well regardless I need to shoot more and within the last month I have shot 500 or so rounds through it.  I only have 14 rounds of 165 gr. and 155gr. underwood ammo.  that 155 is loud and snappy.  but I shoot best with 165 and pbr's 200gr.  so I need to order more 165 and 200gr. in true 10 velocity and narrow down my one and only grain. 

The early G-20's had less chamber support from what I saw in pictures, designed as a combat weapon for reliability.  Although Norma made the Hot stuff back then, I don't think many saw smiles due to the Norma Brass being tough back then.

The recoil buffers are probably not needed, but they do work and serve a function.  care is needed to not have it interfere with functioning.  About your "U" shape slide stop, this also functions as part of the lock-up raising the barrel up to the slide.
T.R. Graham's are said to be really good...call (832-695-7192) or shoot him an email (GRHM458@CS.com)  I am in no way affiliated with him or am I using the product at this time.  I will say I have considered getting his product as a replacement when that time comes.
You can see pictures and read more here http://glocktalk.com/forums/showthread.php?t=851754

Well my PiC is to big to show the " u" I'm talking about.

What exactly does that piece in the link do?

I did notice during my day at the range one of my six mags would fall out after the last round was fired/loaded.  What would cause that?  I shot with it several times to make sure it wasn't a fluke or me pressing the mag release.

TR Graham's MGSL  "Match Grade Slide Lock"  it is said to improve groups and more reliable lock ups.