Hi I’m having issues with m DB g18c it will fire 2/3 times then fizz out I rack the slide & get the same thing this is when I’m pointing it at a target.but when I rack the slide rest my elbow on my hip blaster pointing to the sky I can shoot of the whole mag of gas (50 to 60 shots) any Ideas?
Hammer might be lite striking the release valve and it’s not giving enough pressure to cycle properly, pointing it up might be giving it enough weight to cycle properly, that’s the first thing that comes to my mind, but I don’t know a huge amount on GBB’s.
Don’t have much experience other than my old FB G18C experience, but there’s a couple of things to consider.
Light striking on the gas valve sounds most likely, which you can try spacing out the gas valve a little with an extra/thicker o-ring under the valve to allow the hammer to open it up further.
Make sure to lubricate the valve itself with a drop of silicone oil, easily done when mag is empty of gas and depressing the valve open to add the oil.
Also make sure to lubricate the mechanisms, rubber bucking seal and the slide rails themselves.
Also try out different gasses if still having issues, depending upon what is recommended for the climate/temperature range you are using it in.
Good luck 
Thanks for any Ideas you can give but every thing is well lubed & I have 2 mags and no diff so the depressed valve may not be the issue I have noticed that the hammer wobbles around in the casing it sits in maybe not striking every time.
A wobbly hammer is definitely not a good thing for sure!