Reloading for a M1 is the Pandoras box of reloading. I would think you would not need this plug is you load powder on the light side.
Garand safe reloading data is well known. If you reload, this plug is not needed. For simple Garand safe hunting ammo, just look up "Mexican Match", easy and done using mil-surp ammo.
For those that do not want to fool with reloading, this type plug works well.