Anyone ever drill out their spray gun tip?

I see no reason why it will not work fine. Assuming your gun is already probably 1.3 or so, 0.7mm is only about 0.03" more. That being said, it will make a big difference in shooting primer. I use 2.0 or 2.2 depending on the primer. And if it doesn't work, you are only out $0. Will it be hard to find a 2mm drill bit? FWIW, a 5/64 drill bit is almost exactly the same as 2mm.