I called aoa and asked if you could put an arrow barrel on a standard mk2 verminator (not the extreme) today and one guy said yeah .22 you can put an arrow barrel on it. (went and put money in my account) I called them back to order and a new guy answered. He said no it has to be .25 or bigger. I'm kind of lost. Anyone out there with a .22 standard mk2 verm with an arrow barrel?