[ I'm trying to work up a 300 rum load with 200smk's. how can i figure the c.o.a.l. for this load??? ]
Find the point where the ogive contacts the rifling and seat a dummy round at 20-30 thousanths deeper. See if it will feed through your magazine. If it won't, seat deeper until it does. When you get something that functions reliabily, develp your load for that lenght.
Later, after you've found your most accurate charge, you may want to experiment with seating a tad deeper and shallower to see if you can improve accuracy.
Don't jam your bullets into the lands with that magnum round. That has too much potentail for raising pressures very high.