From my other 30BR thread:
Let's assume that the base of the bullet will be sized 0.3086", and we want the entrance to the throat to be 0.001" larger than the bullet so the bullet can enter the throat without shaving lead or popping off the gas check. The throat will start out at 0.3096" and taper to 0.3006" (the exact bore diameter will vary, but that's a convenient number to use ), or 0.0045" taper per side.
Let's look at how long the tapered section would be for various throat angles, assuming 0.0045" taper per side:
0.5 degree = 0.52" long taper
1.0 degree = 0.26" long taper
1.5 degree = 0.17" long taper
How do those taper lengths match up with a 125 - 130 gr. cast bullet? When seated 0.13" deep -- which I consider a bare minimum to grip the bullet securely -- there will be about 0.300" of bearing length outside the case, so it looks like a 1 degree throat would be a better match than the current 1.5 degree throat.
In hindsight, the problem with the original 1.0 degree throat is that I simply cut it a little too deep. I may try again after I give the current 1.5 degree throat a fair chance to prove itself.