Hmmm welll :-
1) It's got a belt and frankly the cases are not made uniform enough to make it useful which is why folks size to it seats on the shoulder like a normal rimless case.
The folks at Norma and Nosler would be interested in knowing that their cases are not uniform enough to be useful. Norma has a pretty good reputation for good brass and Nosler cases are individually weighed and packaged accordingly. For that matter I’m sure Federal, Winchester, Remington and Hornady would be surprised to learn their brass isn’t useful either. As would many of the hundreds of thousands of shooters using the .300 Win Mag and the millions of game animals taken with the round.
I agree the belt is unnecessary but that is true for all of the belted mags except the original H&H designs. So include as “useless” all of the belted Weatherby rounds, the Remington 6.5mm, 7mm, 8mm, .350 and .416 mags, the .264, .300 , .338 and .458 Winchester Magnum, 6.5 and 7mm STW, .358 STA, .308 and .358 Norma, .416 Taylor, .458 Lott, .470 Capstick and any other belted cartridge that doesn’t have an H&H-like length and taper.
While we’re at it, let’s be honest and admit rimmed cartridges aren’t useful either, as the rim really isn’t any more necessary than a belt except perhaps in break-open rifles. So dump the .30-30, .307 Win, .356 Win, .375 Win, .38-55, .444 Marlin, .45-xx, .30-40 Krag, 7.62x54 Russian, and others - including, of course, the .303 British.
None of these cartridges are useful? Right!
By the way, not everyone sizes the belted mags – including the .300 Win Mag – to headspace on the shoulder. Most of the folks I talk to, in fact, full length size to ensure proper feeding and chambering during a hunt. I’ve been loading the 7mm Rem Mag since 1982 and the .300 Win Mag for several years and have yet to neck size my first case. Sub-MOA accuracy is easily achieved with both cartridges so I don’t buy your arguments. Reality trumps theory.
2) The neck it too short to allow proper seating of the linger heavier bullet for which the cartridge was designed
As far as I’m concerned, the sweet spot for the .300 Wiin Mag is with the 180g bullets. Unless I’m wrong, the .300 was designed to shoot them as well (along with lighter bullets). While it is true that the .300 neck could be longer, the advantage of a longer neck is more theoretical than practical – any advantage would certainly be of more use to benchrest shooters than hunters, although the .300 Win Mag has done well in both arenas as is. As to the heavier bullets, no one I know uses the 220g bullets but folks that use the 200g bullets seem to be quite happy with them. Woodleigh even makes a 240g for the .300. If a .300 Win Mag with a good bullet can’t do the job, a .35 Whelen isn’t going to give me warm fuzzies.
Belts were designed for break action rifles to enable reliable extraction and seeing how America is now the land of bolt action rifles and was when the .300 WinMag came out the belt was put on as a marketing gimmick "as Magnums have Belts" Sigh!
Again, I agree the belt is, as I’ve often called it, “a useless anachronism”. It is, however, fairly unobtrusive – much less so than the rim on the .303 British which still maintains its popularity up north and, I assume, in other parts of the world. Those that choose to do so can easily neck size their brass and a belt (or rim) in no way impedes this.
Nevertheless my guess is the day of belted mag cartridge design has come and gone and I don’t expect to see any new belted mags introduced by the factories any more than I expect to see new rimmed cartridges. Instead I expect the new .375 Ruger case will be the parent case for much of the new cartridge design in the coming years – no belt, no rim, more case capacity with no loss of magazine capacity, and a .30-06 length. I have to say I’m looking forward to the Ruger’s offspring.