Airsoft M203 Shells/Gas help?

Today i received my ICS M203 RIS version, and i got 2 deep fire 180 shower shells. When i put some green gas (http://www.airsplat.com/Items/GG-Bestek-G1000.htm) it had extremely poor range when i shot it. So i put the gas in for about 20 seconds (which i know is an unreasonable amount) and i let the shell warm up to room temperature, only then did ONE shell work properly. it was awesome btw. anyway, I dont have a leak and its not the ball bearings. I think i may need a new adapter for the nozzle of the tank. Im just using the one that comes with it. It fits properly, but i dont know why it does this. I have to gas it sooo much to get it to work, and im already out of green gas!!! im going to the store to get propane tomorrow, and i need to know of a good adapter to get that will fit my m203 shells. i know its not the little circle thing on the back of the shell that you have to push in to reset the gas thing, cause ive done that, and the pressure still sucked ***. someone help im really mad cause i spent alot of my christmas money on some shells and or gas that doesnt work. well, at least work properly.