Most of the concern about low pressure is to protect the wood as much as the metal. Period shells were loaded to much lower pressure and lower velocity than current shells. These 1300-1500 fps shells put unwanted stress on both stock and action. If you load correct pressure and velocity shells the shell length is not super critical. You do get a slight increase shooting longer shells in shorter chambers but it has been estimated to be under a thousand psi which good condition guns can handle.