Is there any particular reason why you chose to use w748 for 308?? I'm going to guess either you have some already or your reloading progressively? As far as if you "need" to use a magnum primer, I would say if you need to use a magnum primer for proper ignition in any short action cartridge with powder fill <50grains, you probably need to re-examine some other factors such as the type of powder you are using. H4350, Varget, IMR 4350, R15 are all great options. The trend in the PRS and long range shooting community has been to switch to SRP as much as possible (hence companies such as Peterson and Alpha coming out with SRP 6.5 creed brass). Im no scientist, but it seems with the smaller/tamer ignitions with SRP, it helps with consistency vs. the violent ignition of a LRP or magnum primer. Other issues you can look at for hang fires are primer seating depth, if your powder has "clumped" or absorbed moisture, firing pin protrusion (usually not an issue), or if there are any obstructions within the flash hole prior to seating a primer.