po'boy: are you reloading for bolt gun or gas gun? type of brass? It does make a difference. Having said that, 42 RL15 does wonders with LC brass in my M1A with 168 or 175 smk loaded at maglength 2.80". Used it in the M1A match at Perry this summer and was in the top 10. With bolt gun and lighter brass (win or lap), would start at 42 and work up.