what is the best ammo to use for a gsg 5pk pistol... .22 cal. brand and grain?

any .22 is going to jam sometimes on you, that is just the nature of that caliber. Using the 40 grain is good but look for high velocity and if you can find full metal jackets I find they work better than soft points. I have heard some people say that hollow points dont work well in the GSG5s but I have not had any problems with mine...again I think the key is to get high velocity ammo. Using the Federal bulk pack I have very few malfunctions. I also have had good results with CCI. I never use Blazer in the GSG5 unless its all I can get, lots of jams with Blazer.

My experience with blow-back operated semi-automatic weapons is that they require high-velocity ammo to function properly. In other words, buy copper-plated federal bulk-pack ammo, or CCI .22LR high-velocity rounds. Look for ammo with higher muzzle velocity, try several brands, and you should find some that work best.

cci mini mags seem to work well in gsg5