The Pedersoli Hiwall comes in 2 models the "Classic" and "Sporting". There is a big difference in stock dimensions with the Classic model being much higher at the comb and more suitable to precision prone work, than shooting offhand with the Sporting model.
I have developed loads for mine using a 220gn (0.380) , 260gn (0.380) and a Paul Jones 375gn. The 1:12 will shoot them all with good accuracy.