Several cartridges that come to mind to me when I read this post. Many of you have talked about them.
I will never understand why the WSSM cartridges were not a success (I don't know anything about the "law-suit"). I had a 25 wssm and loved it. No feeding issues whatsoever. I wish I had it back.
Another great (IMO) is the RCM cartridges. They were excellent to me. People always point to the fact that they didn't do anything the 300/338WM didn't do (YES, they did from a 20" barrell!!) 300WM from a 20" barrel will not do the same thing as a 300RCM from a 20" barrel. I have found that mostly in the hunting world lightweight short compact rifles mean NOTHING. Everybody seems to think they need a 26" barrel and a 6-24x56mm scope on a rifle that weighs 11lbs to shoot a whitetail at 100 yds. Give me a 20" 300RCM and a 2.5-8 loopy and call it a day!
Lastly, the 358 Winchester. HOW THE HECK IS THIS NOT THE MOST POPULAR BIG GAME CARTRIDGE ON EARTH? I have never once seen a box of 358 in any of the gun shops I visit and online its pretty scarce.
I think what killed the RCMs was lack of components, and Hornady using proprietary powder, brass only available by Hornady, etc.... People were not getting, by handloads, what factory was claiming and achieving..
As for the 358, agree, and the 338 Federal should be a lot more popular than they are...