There's something about AIR

For those that started way back in the day, you used co2.  Screw in the tank, cock the marker, and take off the safety - done!  The only real thing you needed to know was how many ounce tank you wanted.  Now there's compressed air tanks and this causes so much confusion.  I find myself helping a lot of people understand what it all really means for them.

First, there's size which is expressed generically as 'ci' (cubic inches).  This is the physical volume inside of the tank measured in cubic inches.  The bigger the number the more volume the tank thus more air.

Second, there's the tank pressure which is measured in psi (pounds per square inch) and most tanks are 3000, 4500, and the rarer 5000psi.  The higher the number, the more air can be crammed into the tank.

Now let's talk about what these mean.  The amount of air (shots per fill) will be based on both of these numbers.  The 3000psi tank averages about 10 shots per ci of size and the 4500's about 15 shots per ci.  So a 68ci/3000psi tank would have about 680 shots - a 68ci/4500psi would have 1020 shots.  Same volume yet drastically different shot counts.  Generally speaking, start by figuring out how many shots you want to have per tank fill.  Then use that to calculate back to the sizes that will give you that shot count.  One note, if you're looking for around 750+ shots, you're almost guaranteed needing a carbon fiber 4500psi tank.

One common confusion - my gun can't handle 3000 or 4500 psi of pressure.  It doesn't need to.  There's a pressure regulator on the tank (that's the top part with the gauge) that will drop the internal pressure from the 3-4.5K down to somewhere between 400-850psi.  The output pressure of the regulator is what actually goes to the marker.  The pressure output is referred to in low pressure (400-500psi) or high pressure (650+psi).  This leads to this next confusion.

High Pressure vs. Low pressure confusion - There are two problems this causes.  If you're not familiar, you might confuse a the high/low pressure reference to be about the psi capability of the tank. i.e. 3000psi is low pressure and 4500psi is high pressure.  The tanks pressure rating is completely separate than the output pressure rating.  Second problem, which does my marker use?  The simple answer is that almost every marker readily available now can use a high pressure tank.  There were a few markers made by WDP on the Angel line that required a low pressure tank.  Blowback markers most definitely need high pressure to shoot and re-cock the marker.  Many of the mid to high end markers run such a low operating pressure that a low pressure tank could be used if needed.  Especially if you're buying the tank, get high pressure one anyway since it'll have a better resale value (usable by more markers) and won't limit you if you change markers.

Another confusion happens when people get a smaller ci tank because they want a more compact setup. Not always true. This is because some manufacturers make the tank shorter but wider making it more compact yet still hold more air.  Also, the pressure regulators are not uniform in size so this will add or take off from the overall length of the tank.  I had a friend wanting to swap out his 68/4500 Pure Energy tank for a 48/4500 because he wanted a shorter tank to bring his marker in tighter to his body.  The problem there was going to be the loss of about 300 shots per fill.  I did some research and found that he could get the Guerilla Air 68/4500 which would be just a bit longer than the 48ci he was looking at without sacrificing the shots.  It's really due to their super short regulator.  The Ninja 68/4500 was also a full 1" shorter than the old tank as well. I ended getting the Ninja myself and really like it.