There are a number of issues.
Index your feed rate. For 303 use .004 x diameter x number of flutes x RPM.
Adjust your your average chip load by new IPM = old IPM x sqr( dia / width of cut)
Adjust your cubic inch per minute by square of the diameter of the tool. And by the inverse cube of the length less 1/2 the z depth of cut. new CIPM = old CIPM x (dia^5/(length - 1/2 depth)^3). The maximum value not to exceed new CIPM = old CIPM x dia^2.
To adjust for HSM, use this: new IPT = square root (old IPT x old CIPM / (w x d x nt x rpm)) w = width of cut, d = depth of cut, nt - number of flutes(teeth) and RPM your going to use. old CIPM = w x d x IPM or reference CIPM for your tool.
Start with .004 x 3 flutes x .2 depth x 1 (for a 1.000 cutter.) use the dia^5/(length - 1/2 z depth)^3 to adjust. As a starting point. new CIPM = old CIPM x new (dia^5/(length - 1/2 z depth)^3) / old (dia^5/(length - 1/2 z depth)^3)
Adjust your CIPM up or down accordingly. Down if you break a tool (70%) or up if it works 10% to 20% at a time.
Once you find what works best, you can then index it per tool dia and tool length accordingly. dia^5/length^3