I predicted a LOT of failures, and fail they did...
The WSSM family: these were an uphill battle against some well loved cartridges. The .25 was an obvious insta-flop (Americans as a whole have no love for the quarter bore), but the .223 and 243 WSSMs didn't fare any better.
The RSAUM family: it was going to be RSAUM or WSM, and frankly WSM was marketed better and rolled off the tongue easier.
The WSM family: the .300 and .270 were all that stood a chance...maybe the 7mm IF it hadn't been released late. Weight shaving elk hunters are a niche market. I see more of them packing a long mag, coping with the weight, and reaping the performance.
The RUM family. It was going to be .300 or nothing here....and it is. Fastest way to toss a 180-220gr .30 cal without going to proprietary Weatherby cases...but the loaded ammo still costs as much. The others? Nope.
The RCM family: there is "fashionably late" and then there is "Dude, the party was yesterday!". Not really sure what Ruger was thinking here. The stopping rifle category is small and full. The "long-range 20" brush gun" category...does that niche even exist?
.338 Federal: this is faring better than I had thought it would, and I must say I'm shocked. Introduced into nearly nonexistent gap between the .308 and .358, but lacking the powder capacity to drive heavy bullets fast & flat, I admittedly called this one wrong.
The Marlin Express family: nostalgia wasn't going to make western hunters trade their '06 or .270 for a proprietary round that offered less performance, in a gun that offers less inherent accuracy, and just ONE bullet choice. Eastern brush hunters didn't need the thing. I liked the idea of the .308 MX, but knew what would happen. The .338 MX was wishful thinking on Marlin's part.
The .450 Marlin: a niche round with a lot of potential, un-seating the .45-70 was always going to be a tough row to hoe. My understanding is that it is being kept alive in Alaska. A bit light for Africa's heaviest game, Alaska was always its one true home.
And from history:
I'll trot out my favorite, the .257 Roberts: a 57mm case factory loaded to match the length of a .308's 51mm case, the deep seated bullet eats up powder capacity, and makes a long action wasteful for all but hand loaders. It comes factory loaded at 2 levels: a "standard" light load that equals the .250 Savage, and a "+P" that is only a +P because some old, weak, military guns (Mauser 88s & Japanese "last ditch" rifles) got themselves rechambered to it. Factory ammo is often loaded with 117gr RN bullets intended for the 25-35.
What is to be gleaned from the .257Bob's tale? Simple: like the 7mm-06/.280/7mmER/.280, and the .244/6mm, if you want to kill off a cartridge, just confuse the shooting public.