It depends on the starting distance relative to each other. At max. M4 range, say 400 meters, the Marines have a chance, but much closer and the Spartans are on their ass within a minute. Sure, you might kill half of them, but then there's still 2500 pissed off Spartans to contend with.
The Somali's don't count since a third would struggle with the safety or shoot his buddies by accident or some other hilarious fuck-up.