setup.I went from the bulk CO2 QB78 to the HPA QB79,and a used SCUBA tank.It cost me about a $110 for a used tank,inspection,and fill.I bought a used yoke for filling for $35.The only problem I had with the tank was it has a J valve,instead of a K valve that's for reserve air when you dive.So I had to mill the other side of my yoke to clear over the valve like the other side did.I did this in class one night for nothing.I was so happy with the HPA I swapped one of my bulk fill CO2 pistols for a combo Disco..177/.22 with a hand pump.I fill the QB to 2500(because that's what tank pressure is now)than hand pump it to 3000.The Disco. I just fill.It was .22,now I switched it out to .177 to diversify.Yes you can have your QB78 tuned to HPA,and still use CO2 with it till you want to use the HPA,but don't mix them! Same deal with the Disco. you can use CO2 fill up to roughly 850,than if you want exhaust tube than fill to 2000 HPA.The CO2 is affected by weather temps. the HPA is true blue no matter what.Once you have the hand pump it don't matter which gun you get.There are guys out there that mod. the QB79's like mine that shoot low 800's,and have plenty of shots with that 13cu.in.front tank set up.It's not as clumsy as it looks,and for all the advantages it allows you it's worth what little inconvience it may have.I like the higher fps with the HPA,more air reserve,plus not effected by the temp..That's MHO.