I am making 7.62x40 brass from LC 223 for ar15. The specs call for a neck length no longer than 1.570. i measured the throat using a sized case. Cut most of the neck off. Then cut another small piece of neck off another case. Seated the bullet to mag length. Slid the small piece of neck over the bullet and then chambered the round. oal stayed the same. I got a neck length of 1.590. My question is do i want the neck as long as will fit in chamber. Is there any benefit to a long length neck.