The problem here is not one of chamber pressure, but of port pressure. Port pressure is the amount of pressure remaining in the barrel of a gas-operated firearm, when the bullet passes by the gas port. The Garand was designed for use with medium burning rate powders 4895 and IMR 4064. Using a slow-burning powder such as 4831, even if the load develops relatively mild chamber pressure, will still give excessively high port pressures. This causes violent cycling of the action and can result in a bent operating rod. Load your Garand with only those medium-burning powders that are compatible with its gas system.