eddief,
There are many variables involved in determining bushing size for your given cartridge but one thing i will tell you now, is that in order for bushing dies to work at their best, you must neck-turn your cases.
Descriptions on all these methods can be found in previous posts on this forum,try using the search option to see what you can find.
Basically, if you have a factory chamber, turn your necks to 3/4 clean up, seat a bullet, measure the diameter of the neck with bullet seated and select a bushing approx. 002"-003" smaller then this measurement.
With a custom chamber it is a bit more involved, you need to take into account chamber neck diameter, case neck clearance and turn your necks accordingly but again select a bushing two to three thousandths smaller.
If you have not done any neck turning, again, complete descriptions can be found in previous posts.
Ian
"I meant to shoot the pike but the duck got in the way"