Help with a countersink

A little background…So basically I have a handful of aluminum sprockets I have to mill out. Each sprocket has 5 5/16 holes and they all need to be countersunk. I have done some math and have come up with a hole size of 5/16, a screw head diameter (and widest section of countersink) of .656 and a plunge depth of .328 on a 90deg countersink bit. I do not have a countersink bit wider than .500 nor can I find one reasonably priced for aluminum with a 1/4 shank.

Here is my question. (99 percent of the time I use Vcarve but am open to easel if I must) How do I or can I run a toolpath to sort of chamfer the countersink? Im not sure how to word it but I am imagaining a 90deg bit moving in a circular motion reducing z height with every rotation. Is this even possible?

Most of the time I use vcarve. I have found a way to run a profile toolpath and under the ramp tab you can choose spiral. This would be perfect if you had the correct size tool for every countersink. The dewalt only accepts .250 shanks and smaller and i have been unable to find a chamfer mill larger than .250 with the correct size shank. I thought about carbide tipped V bits but im afraid those will chatter and not give the correct chip load.

I just dont understand why you cannot have two circles one the screw head size and one the screw shaft size. Select both vectors and designate a spiral ramp to a designated depth. Very frustrating.