Hi-Caps rattle like... a baby's rattle!
If you're saving money. a site like ehobbyasia will sell you a pack of 10 plastic lo-caps (85rnds, for instance) for less than $30 US. Just beware their shipping rates look scary high. Hi-caps can also be distracting from the "realism" aspect of the game. On a thread concerning "Pet Preeves" (their spelling) a common peeve was players using hi-caps.
Delenda Est Carthago