This buttpack looks a lot smaller in the pictures than it actually is. Each of the side pouches can comfortably hold a 700mL plastic water bottle (used for storing bbs, water or whatnot).The main pouch is large enough to put a drum mag and a set of sporting binoculars in comfortably. It was a lot bigger than I expected and it works great in skirmishes (all i ever do anyway). This buttpack is a very functional device and well worth the buy if you have a need to shove large things into small spaces.
Large main pouch volume
Large side pouch volume
Top pouch is good for storing pistol mags
Secret compartment is great for keys, barrel plugs and other things you don't want to lose
When combined with a belt it can replace practically all the gear that one needs for a 3 hour game (running hi-cap and drum mag)
The roll up buckle on the main pouch is somewhat annoying
Not snow-proof so plastic liners are a necessity. I live in Canada...