TopCat,
From what I heard from people in the industry, the .325 WSM came about because Winchester couldn't match the ballistics of the .338 Winchester Magnum when using the WSM case. And they had claimed they could match .300 Winchester Magnum ballistics with the .300 WSM, which was true ONLY because the common SAAMI muzzle velocity with 180-grain bullets in the .300 Winchester at the time was only 2960 fps. (Since then there have been two other SAAMI-acceptable velocity levels created for the .300 Winchester Magnum, both higher.)
Winchester claimed that the .300 WSM was able to match the ballistics of the .300 Winchester Magnum due to the magic shape of the WSM case. This was BS. Nobody in any ballistics lab has ever found a smaller case that can match the velocities of a bigger case thanks to any magic case shape. Instead it was due to the somewhat wimpy .300 Winchester factory muzzle velocity.
But the Winchester publicity BS also forced them into a corner with the cartridge many shooters expected, a .338 WSM. They found the .338 WSM case could NOT match .338 Winchester Magnum velocities with 250-grain bullets, because the long bullets took up too much powder room. Also, due to the short magazine, many existing .338 bullets had to be seated too deep inside the .338 WSM case the ogive to remain outside the case neck.
So Winchester side-stepped the whole deal by claiming they'd developed a cartridge equal to the .338 Winchester Magnum using 8mm bullets. This also turned out to be BS, because the only factory-loaded bullet over 200 grains was a Power Point that didn't penetrate nearly as well as the premium 200-grainers also used in the .325. (I know this partly because a hunting companion brought a .325 WSM to South Africa for a month-long hunt I did in 2007. Within a few days his PH told me he had to switch to the .375 H&H he also brought along, with 300-grain Trophy Bonded Federal loads, because the 220 Power Point simply wasn't penetrating deeply enough on larger plains game animals like zebra.)
As a result the .325 turned out to basically be a .300 WSM with slightly fatter bullets, not a .338 with a wide range of bullet weights up to deep-penetrating 250's. And anybody who looked at the downrange ballistics found 180 and 200-grain .300 WSM loads caught up to the .325 180 and 200-grain loads within about 300-400 yards.
That doesn't mean the .325 doesn't work. It does, just like the .300 WSM, or any cartridge with 180-200 grain bullets of around .30 caliber at those velocities. But that doesn't mean it somehow matches the .338 Winchester Magnum, any more than the .300 WSM will match .300 Winchester Magnum muzzle velocities due its magic case shape.
I well remember the marketing--Winchester could just as well named them the WBSM's.
Edited to add, not that they do not serve well but they are not quite equal to their corresponding "long" magnum counterparts, all things being equal. For example, I remember specifically, with the 270 WSM, the Winchester advertisement showed this WSM equaling and beating the 270 Weatherby at four hundred yards with a sleek, high BC bullet compared to a bullet with the BC of a tomato out of the Weatherby.
A little hyperbole there but the point is a real one.
