Me and a friend have been toying with the idea of a moderator for Bp rifles for some time but the moderator will have to be removed to load every shot, then the size of the mod as 1 gram of bp will produce 270cc of gas (1 gram = 15.432 grains) a 30 grain charge will produce about 540 cubic centimetres of gas, that's just under 9 liters of gas the mod will have to handle but good luck and keep us posted (we are having noise issues regarding Bp at the club, highest load in a pistol is only 20 grains)