To be honest, unless I have it in my hands, I'm not able to see what your potential problem causes are, as I'm not given enough information based on your descriptions. Particularly if this is your first gun of this platform, you may not know what to look for.
When I pick up a problem gun, there isn't a particular checklist I go through to find problems... I just look at it and look for what's out of place. Of course, this comes with experience, and I am not expecting you to be able to do the same.
For what it's worth, your build should be able to punch through a soda can. I would check all the areas relating to seal (nozzle, piston head, rocket valve, hop up rubber and barrel), and ensure all is good.
|