The barrel length is really up to you and the balance of the gun. Somewhere between 28" & 30" would be a logical choice. As for "tight neck" VS Norma chamber. You will generally be better off uniforming your case necks to make sure they are perfectly concentric. However, some think this is an unneeded step with the quality of the current Lapua brass. BUT TO BE SURE YOU SHOULD TURN THE NECKS. So it's up to you to turn necks or not. But the 100/200 Yd guys all turn their necks. You will probably be shooting farther than that. So you should probably go for the tight neck if you want the Nth degree of accuraccy.