What caliber., 5.56? What ammo works vs what doesnt work?
Sometimes the gas port has to be enlarged to operate a piston gun. Its a lot more rare these days, but it can happen.
I would inspect the gas block. Is it adjustable? Double check the alignment as crazy mentioned.
Is the oprod and spring aligned properly at the gas block? Is it binding at the upper? Does it line up with the bolt? You should be able to see where gas is being vented after 25 rounds or so.. Piston guns are a pain in this area, they never seem to vent the gases in a good place. If you are seeing discoloration around the gas block, you could have a gas leak....
And as kpk said, a lot of times they need a few rounds to smoothen everything out... How many rounds do you have through it? How did you clean and lubricate the gun? How often/how many rounds between clean & lube? What lube did you use?
With that being said, i would call and talk to someone at adams. They are getting ready to release a piston 308, so i would think they will try really hard to get you sorted out as quickly as possible.
I have never built a piston gun from scratch, but i do have a piston 308... Its gas port is about twice the size as a regular gas 308....