I have developed loads for several WSMs and from what I have see during load development, if your going from safe to dangerous loads in 1/2 grain of powder you are using powder that is far to fast in burn rate.
I generally use Rl-22 and H-4831 for the 300 WSM
Rl-22, H-4831, Rl-25 and H-1000 in the 270 and 7mm WSM
H-1000, Rl-25, Retumbo in the 6.5mm WSM.
If he is using the correct burn rate for the round, then I would say that the loads he is considering "SAFE" are to high in pressure to begin with.
Remember, this is not a huge case in capacity, around 60 to 68 grains of powder capacity depending on bore and bullet weight used. At time slightly more.
What is his criteria for reading excessive pressure?