Mount it to the pic rail on top of the upper receiver. If you are worried about it "Losing zero because of the removable barrel". I had my 510c on the upper receiver and took my barrel off all the time with no issue, used it in competition with no change. Just make sure you have the barrel tensioner done up right and there wont be an issue (with the barrel off, start tensioning and trying to lock the barrel up. When you hit the point when its to tight to put back together, back it off until you can put it back together and then tension it 1 click at a time until it becomes hard but not impossible to remove the barrel. That's your sweet spot).