jcm,
i called nosler and asked the same question... the rear portion of the 150, 165, and the 180 are all the same... the change in construction comes with the 200, in which the partition is moved farther forward leaving a larger rear portion...
all else being equal, the 200 would logically be the pick for penetration in 30 cal...
once again, i'd not split hairs between the 165 and the 180, but i agree with bmt that the 180 is the standard, and i'd need reason to deviate from it..... john w
