Why is the cartridge full of CO2? (Page 2)

I didn't read all of the replied, but my question is:

Why are many of the CO2s threaded?

I saw the response about pellet guns having them, but the ones I had growing up were unthreaded. They also have similar handheld CO2 cartridges for dislodging bullets from a muzzlleloader, of which aren't thread either.

Ooo Ooo I can answer this one!

You can buy them either way, just depends on the delivery system you use as to which one you want.

The system I use I screw on a valve until it punctures the cartridge then unscrew it enough to let the Co2 start coming out. Very small setup and actually mounts on my bottle holder setup. Other setups use a different system to puncture the tube but they are usually bigger in size. 

got it, I need to find the one that doesn't thread.

I have a fair amount of CO2 cartridges laying around from way back when. And they are cheaper at walmart than my lbs