Definitely sounds like something is restrictions the bb on the back side of the bucking/hopup. If you say the hopup is all the way off, maybe there is an issue where the hopup isn't actually turning off. The adjustment screw may be turning, but its possible that it's not doing anything but turning. So, if the hopup is on too much, that can slow the bb down a ridiculous amount. Clear the chamber from any bb's. Then do a dry fire towards the floor.. THEN do a dry fire into your hand and see how much air pressure comes out of the barrel. Could be a ripped bucking, stopping the bb from moving thru freely. Could be a stuck hopup arm/actuator. Could be a nub, lodged sideways even. Wont really know till its taken apart and inspected.