So far, neither the original post nor the rest of this thread has addressed the real reason for designing cartridges with long necks.
Neck length is more important to the interior ballistics of a cartridge than to its exterior ballistics. The longer neck holds a fully seated bullet tighter and for a longer time than the shorter neck, for more-efficient burning of the powder charge. Neck tension (bullet pull in ballistics lingo) is a vital component of efficient interior ballistics.
Also, there's the matter of what I call socket engagement for better alignment of the bullet. Consider the safe depths to which you must seat a fence post, a telephone pole, and a flag pole, and you'll begin to see the importance of socket engagement. Six inches to a foot may be deep enough to seat a fence post just long enough for you to get out of sight � but it won't be deep enough to keep the post vertical for very long. The longer poles need more "socket engagement" � and so, IMO, do the longer bullets. The more of the pole (or bullet) that's exposed above ground (or the mouth of the case), the deeper that pole (or bullet) must be seated to be held adequately firmly. Seating a longer bullet deeper in a short neck is only a partial "solution."
The original design of the cartridge should provide adequate socket engagement for the lengths of the bullets that the cartridge is designed for. The twelve cartridges in my .220-to-.400 Howell series all have 0.375-inch necks for good socket engagement with heavy bullets, which are all very near the same length in all small-arms calibers. The longer necks align the longer bullets more reliably. Neck length, then, is more of a matter of how the neck length relates to the length of the bullet rather than to its diameter.
The fad and fetish of the highest possible velocity without regard to any other consideration, either interior or exterior, is responsible for both the lighter bullets being favored and the shorter necks that are all that the shorter bullets need, for either adequate socket engagement or adequate containment of the faster powders that the shorter bullets favor.
