I can actually give you a legit unlimited ammo glitch lol, (it's not exactly unlimited, but near enough):
- You need to have at least 2 people with Monkey bombs and 1 person with a raygun (makes it easier). All you do is, wait for a power-up, throw a monkey bomb once you see one and wait for a monkey to come and take the power-up, then follow the monkey until it lands on max ammo and kill it with a raygun (large splash damage/area)

Tell your friend to throw a monkey bomb if you need more time.
Trust me, it's sounds stupid and simple, but it's actually an amazing tactic. Just think of it as a max ammo, EVERY ROUND. BEAST. :fyea: