Gene,
It sounds like you're looking for a 7mm Rem Magnum barrel to put on an action fitted for a 280AI. Apologies in advance if I'm stating the obvious but if your action is fitted for a 280 AI, it has standard bolt face (0.470+/-). The 7mm Rem Mag will require a magnum bolt face (0.540 +/-). Might need to order another part (or two).