Oh you'll figure it out when you get on the field.
They rattle like maracas because it's fed from a "well" instead of a "guide track". With the well, BB's are allowed to move freely and suffice to say, will make a lot of noise when not 100% full.
Not bad if you're just starting, no one will fault you for that however there is a "stigma" associated with running with hi-caps.
Also if you're playing milsims or want to Hi-caps are usually banned or at least severely limited.
Get a mix of mids and lows as soon as you can but there is no problem with playing with a hi-cap for your first few games (or if you're poor like me..... I just spent like $800 on textbooks and other school stuff so I'm in no position to be buying any more gear).
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE