I am doing some 2" X 2" X 2" 17-4 PH aerospace parts that are quite involved with about 5 setups (bores, radii, angles, profiling, form tools, etc.). The first setup uses some 13 tools. Anyway I'm using a Mitsubishi .750 dia. three inserted end mill that roughs out most of the material. With flood coolant the inserts lasted about 4 parts. Cutting dry the inserts last about 10-12 parts, or 2 1/2 to 3 times longer. So the moral of THIS story is; if you're having insert life problems cutting 17-4 or 15-5, - try running dry to see if there might be an improvement. Check your inserts frequently the first time you try it so you don't fry your cutter body. We used to use Iscar cutters, but since Mitsubishi replaces their cutter bodies if they are destroyed, we've started using them almost exclusively, at least in the smaller sizes.