think ive cleared this one up a couple times before
just because a marker will fire at a rate of 13.5 bps does not meen that 13.5 balls will leave the barrel in a second
the 13.5 bps refurs (spelling) to the time taken for the marker to cycles ie, its cycle speed (rest-fire-rest) is 1/13.5 seconds
the only way it would actually fire at 13.5 bps would be if you could physically pull the trigger that fast (or faster) constantly for a second.....and before you say it....you cant! otherwise you would be emptying a loader in less than 20 seconds