Pappy,
My Tikka .260 has the standard SAAMI throat and magazine length, and I can't even seat 140-grain Nosler AccuBonds out to the lands. Or at least I couldn't before modifying the magazine to 3". (I tried a long-action Tikka magazine and it wouldn't feed .260's reliably.)
Another factor in the general downfall of the .260 is the suck selection of factory ammo. Remington dropped most loads pretty shortly after introduction, and while the Remington website lists a couple of 120-grain Accutip loads, the 140-grain Core-Lokt is the only load generally found in stores. It shoots OK in my Tikka but doesn't come anywhere close to the listed 2750 fps muzzle velocity, averaging around 2550. Most Campfire members are rifle loonies and therefore handloaders, but average hunters aren't, and for any cartridge to be popular with them there needs to be decent, affordable ammo in stores.
In contrast, Hornady has kept a good variety of 6.5 Creedmoor loads out there from the get-go, and continued to add to their list, especially with lower priced but accurate hunting loads.
Even in the late 1990's Remington should have had their finger on the pulse of shooters enough to foresee the increasing popularity of high-BC bullets. In fact the .260 first became popular among silhouette shooters, which should have provided a clue.
