If someone needs it, the formula of how much WPP a nth level of WM will give is : WPPs = 5n²+25n
I don't think this is right (unless it ninja changed last night or something  ), based on both my and other people's observations.
), based on both my and other people's observations.
Kafein is correct; his formula gives the 
total WPP gain from an nth level of Weapon Master. Like if you had 5 WM, it would be 5(5²)+25(5) which equals 250. You'd get the same result from adding 30+40+50+60+70.
Any idea where I can find the exact effects of each point of WPF ? Do the benefits scale linearly with the amount you have ?
I don't know any actual numbers, although Urist said a while ago that 100 melee WPF = 17.3% increase in damage. As far as I can tell though, the benefits (speed, accuracy, damage) do scale linearly.