I believe "Proline" is made by "Darton Archery".You might want to drop them and line and ask about your model (MXV).I am not familar with this one.I know that a couple of their mods use 20" bolts.I think the "MXV" is an older bow that they may not product any more.I would get in touch with them.This is not much,but I hope it helps some anyway.Website....www.dartonarchery.com..........gl....Rick