Gravity feed loaders:
Gravity feed loaders are the most common because of the price; however, they are only a container with a tube ( think funnel ) that loads one ball at a time in the breech of the marker.
These loaders can only feed 5-8 balls per second and are very inconsistent in their feed rates
It is common to have to shake these loaders every 6-10 shots to refill the feed neck.