Originally Posted by
krome
The one on the left in the OP's picture is a used cartridge. The dimple is the hole made by the screwed on head. That solid front is the seal.
Yep. Look inside the screw on head and you'll see a small tube with an angled sharp end, like a large diameter hypodermic needle. That is what pierces the end of the CO2 cartridge to let the CO2 out. The "cheepo" cartridge is normal and should work fine (and look like the one on the left after it's used).