Cutter, speed and feed for cast iron?

I am using a mini mill to mill the lead screw mount bracket for a
mini lathe. The bracket appears to be cast iron. I have tried 2
straight center cutting flutes, 4 straight, slow and high spiral
center cutting flutes. I have tried them at slow speed and slow
feeds, slow speed and high feed and fast speed at high feed. Duh, it
still always tries to gouge into the work either at the start or end
of the cut. The cutters are all 3/8" shank and cutting diameter. Some
are HSS some are carbide coated and non coated.