I am thinking of trying a custom bullet, i have a 6mm br Mark Chanlyn 4 groove 20" barrel 1 in 13 twist, 100-200 yd shooting. Of my flat base, bullet weight choices i have all are a tangent, 6/9 (secant) double radius, 8 single radius, or 15 single radius. what are the advantages of the double or single radius's, and the amounts of radius