In VERY general terms, 20 grains up from = ABOUT 2# of dynamic spine; 20 grains at tail = ABOUT 4 grains of dynamic spine but in the opposite direction. Depending on the speed of the bow and your shooting ability, the 20 grains may or may not show a difference in elevation due to weight.
dchan is correct, 18M/20 yds usually doesn't require a perfect tune.
IF we assume the 410's spine/tune correctly at 30", you're looking at a 2214 or 2311 in X7.
That also assumes you're shooting a bow close to 50#.
“Simple and innocent, however, as it (the bow) appears, and capable as it is of being a trusty friend and ally, a bow is at the same time a watchful enemy, ready to take advantage of the smallest slight.”