The MEC Pro Check is a must-have accessory if you frequently use the Model 600JR loader. This MEC Pro Check can be attached to your charge bar using the bar-stop screw. Once attached, the MEC Pro Check programs your charge bar to keep the loading cycle in the proper sequence it also facilitates automatic operation of the wad guide.For reloaders who prefer the Model 600JR loader, this MEC Pro Check is definitely a handy tool to have around. For a small price, you can enjoy the benefits this MEC Pro Check has to offer it is incredibly easy to use.