HobbyKing for batteries for sure, Lipo's are far superior to the other battery chemistries across the board. I was an old school Nicad,NIMH guy but once I went lipo I'll never go back under any circumstances. As far as size, basically figure out what physically fits for the application largest mah possible for the voltage you'd like and run with it. The Turnigy stuff is good, and I've had fair luck with Zippy too for brands. I run 7.4v in stock guns without mosfets, upgraded stuff almost all gets 11.1v stuff these days. Mah will basically shake out in most guns around a shot per mah, so 2,000mah battery should do around 2,000 shots.
Ballistics is a bear, honestly hotly discussed over the years. And to a certain degree it's weird, it doesn't follow regular firearms in most cases, closer to airgun ballistics but still very different. Airsoft Sniper Forum, not to push you off site but they have been the best discussion of ballistics in airsoft I've seen over the years. Typically because they are trying to shoot the furthest and most accurate rather than other facets of airsoft.
If you're looking for broad facts here is the way I see it, and I will use FPS despite the fact that I know guys will argue it's not necessary for long range there is a correlation. You can't shoot a hundred yards with 150fps(a 6mm BB at least, maybe a proper slingshot). And this is only my 2 cents and experiences.
Sub 350Fps generally well tuned gun you're able to shoot around 60 yards less with less FPS but most things between around 250-350 will shoot 50-60 yards with everything working well and the right parts.
400-450 You can stretch that to 75-80 yards, at 400 75 yards is tough, everything has to be about perfect. That's right on the bleeding edge of what I've seen. Also right weight BB's too, but this can be done with .25g decent grade ammo.
451-550 With this you can hit around 125 yards well actually you need from what I've seen at least around 515 and above to take 125. But around that 500fps range properly tuned you should be able to tag 100 yards with it, depending on all the variables though. Oh and BB weight around .43g maybe a touch more here is about right, good white ammo is hard to find but there are options out there.
550+ Point of diminishing returns, with heavier ammo it's possible to stretch it even further. But you get to dangerous levels of energy with the BB up close. IE if you have a hot rifle and only shoot someone at say 100 yards, no problem the energy has dropped to safe levels. But if someone walks through your shot in the middle at say 10ft not realizing your shooting. That's gonna go bad places. Which is why generally you don't see those high energy guns out there much. I've shot them, and unless you push past .43g BB's into bio ceramics and the price is sky high. You won't see much gain if any going hotter than 550fps.
Hope that helps;)
Luke
