Some Piranhas have a choke velocity adjuster in the front bolt. Unless you have a LONG allen wrench to reach down the barrel, you have to remove the bolt to adjust it. They don't all have this, but most seem to. Out of 5 of my Speed Demon bolts, 3 have it and two don't.
Or you could get a Palmers UMB and put a female Stabilizer on that and use it as a bottonline, and also to control your velocity by regulating the input pressure. Not cheap, but it would be a nice setup.