A Garand needs special ammo? I wouldn't hesitate to shoot anything off the shelf through the Browning.
A Garand with a stock USGI gas plug should only shoot military (or similarly-loaded commerical) 30-06 ammo (such as M2 Ball). The reason why is that the pressure from some modern slow-burning powders can eventually damage the op rod.
However, the gas plug (which simply unscrews from the fron of the gas tube) can easily be swapped out with an aftermarket plug from Schuster or McCann that will allow you to shoot most any commercial loading.