I have the GSG-5 and have tried all kinds of ammo in it because of jamming. I even did all the mods with the gun and still got jams with it. In fact I got so good at removing the jams quickly I just about gave up on it and decided to live with it. Then one day I got a box of Federal(525 rnds in a box) filled all 6 of my 24 round mags and didn't have a single jam that day. Have been using them ever since and it only jams once in a blue moon now.
I also noticed a lot of people recommend Federal for the GSG-5.
Remington, Winchester, and CCI have given me problems with the gun. So now I use those in my 10/22 and the Federal in the GSG. Can't say for sure this would help you but it has made me start bringing the GSG to the range more often now.