Gunpowder's burning rate increases with pressure, so it will burst containers but just burns in the open. Ignition of the powder packed behind a bullet must generate enough pressure to force it from the muzzle at high speed, but not enough to rupture the gun barrel.
The gas constant occurs in the ideal gas law, as follows: where P is the absolute pressure (SI unit pascals), V is the volume of gas (SI unit cubic metres), n is the amount of gas (SI unit moles), m is the mass (SI unit kilograms) contained in V, and T is the thermodynamic temperature (SI unit kelvins).
The equation of the isotherm of an ideal gas is p V = const, where p is the pressure and V is the volume of the gas. For a real gas the equation of an isotherm has a more complex character and becomes the equation for the isotherm of an ideal gas only at low pressures or high temperatures.