I have a set of Leupold MK 4 30mm low rings. I have recently tried to mount them to a Larue tactical base. They will not close enough to grab it. Is this an issue with compatibility with weaver and picatinny or what? I can't find out if the rings are supposed to be weaver or picatinny. The base clearly states to be picatinny. Does anyone know which one the Leupold rings are?