Well when it comes to cylinder volume you have two at least two variables at play at least two important ones. One is the length of the barrel the other is the weight of the ammo your going to be using. The longer the barrel the more volume you need, the heavier the ammo the more volume you need. If you have excess volume, increasing the BB weight will cause jewel creep because the BB is staying the barrel longer and imparting more energy onto the BB. Basically Jewel creep is sort of unavoidable, if you've got enough volume to shoot the heavier ammo it's going to chrono lower with lower weight IE .2g BB's. If you don't have that setup then your undervolume which is also possibly a problem.

To be honest, I personally only use a bang kill ( or surrender for that matter) if its a one on one or one one two, I have a total drop on them, and I cannot feasibly engage them (within MED with no sidearm, ect).  Aside from that, the only time I wont just pop them once in the back is if they have no PC on.  And before anyone says HURRDURR IT"S AIRSOFT, IT DOESNT HURT THAT BAD, I prefer to not be a dick on the field, and if I don't have to give someone an extra welt, I wont.

• Start with rec games and work your way up. In a rec game, you can play for 20 minutes and then sit out a round if you need to stop, hydrate, and take a load off your knees. If you like it, condition your way up to scenario or milsim play.
• Focus on getting good health and safety gear first. You can have fun and enjoy being at a game even if you're not competitive, because airsofters are generally fun people to hang around with. It's a lot harder to enjoy yourself if your mask is always fogged, or if you're not staying hydrated and become incapacitated in the middle of the day.
  
• Don't buy gear for the sake of having gear. Carrying all that crap around starts to add up after a few hours. Going out there dressed like you're going to spend 72 hours behind enemy lines in North Korea just hurts you if the games only last 15 minutes each.