They can be. Try slightly backing off the small screw that holds the biggest wheel in place. If that doesn't work, take the hop and inner barrel out of the gun and turn it back from full on to full off about a dozen times to loosen everything off. If it's still tight, take off the larger wheel and the one it connects to, as it could be the wheel hubs are very tight on the pegs they sit on. Try then opening out the hole in the wheel hub very very slightly with a small nail or similar, or a very fine needle file.