The pellets are loaded into an oblong magazine, and then fed in to the breach via a piece of shaped metal. This shape needs to be set to the length and, to an extent, head shape of the pellet you're using. There are three gauges available. One for accupells/premiers, one for bisley magnums and one for air Arms. They are adjustable as long the pellet head shape is roughly the same.
Just put accupells in it though - it's blindingly accurate with them.
Any questions just ask. I've had mine for years and like to get to know my kit very well.