So yeah, fret cutters if you have them. But what if you don't, and you only want to build one or two and are a cheap bastard like me. Well, if you own a Dremel, the answer will only cost you about $6.
https://www.amazon.com/Dremel-650-8-Inch-Straight-Routing/dp/B00004UDIL
Been using this bit to bevel the forend on M1's for years. Turns out, it does a nice job on the P80 tabs too.
Set the speed fairly high to prevent chatter. Buzz off 90% of the tab, and then slow down and get deliberate...