The M-1 Garand rifle happens to have an action that is about five-eighths of impossible to destroy; they will handle truly outlandish pressures which would demolish another rifle. Not meaning that one should try to overpressure the things, but you DO have that extra insurance when using one.
If any special high-pressure MG loads were manufactured, they weren't any American standard; all their standards have been published, and none exceed garand operating pressures.
The Garand rifle tends to favour higher-pressure loadings, for some strange reason. Maybe it's a Good Thing that John Garand had to leave Canada in order to find work: this country would never have paid him to design firearms!