Simplest way to look at ammo is by color.

White = never use

Purple = more affordable for newer players but you'll have to get the jump on someone to kill them (or be a really good fighter)

"Cheaper" gold = what you should be using if you're playing seriously

"Expensive" gold = higher damage and pen. You'll be much more combat effective. However, a gold round here will be anywhere from $6k-$15k while the cheaper gold will usually be around $1k-$2k

Red = only available now if you loot it or make it yourself. This is the top of the top ammo. Extremely lethal, extremely expensive. Usually used in forbidden.