Wow #112 responses. Makes anything i say a repeat. Anyways, too me this means common calibers that apparently have been surpassed by modern chamberings.
Firstly there are the replacement calibers for ancient or potentially dangerous ones. In a modern rifle, there is no difference between 7x57 mauser and 7-08 rem. Factory ammo is lawyer friendly in the former due to 120 year old potentially liability risk firearms. Lump 45-70/450 Marlin, perhaps 375 H&H/375 ruger, 6.5x55sm/260 rem, and i am sure a lot of others that are effectively replacing/duplicating existing calibers.
Second are the marketing department calibers. How is the 300 WSM a improvement over the 300 Win mag. A fat cartridge and doing away with the belt; however, many of this family are notoriously difficult to handload. We had a number of families of calibers come out, WSM, WSSM, RUM. The super shorts are effectively duplicates of existing calibers and fading into oblivion. The most popular of the WSM is the 300, effectively a 30-06 and a half or a 300 WM minus a half. Only the 270 WSM surpasses in performance a cartridge it was meant to replace...the 270 Win. How is this to happen? The Rum family will be here to stay, considering the popularity of long range shooting. Do they surpass the calibers they are meant too...certainly. They also duplicate or nearly so, new kids on the block of 20/30 years ago or more. How does one live on the difference between 338 Lapua/338 Rum(brass cost perhaps), 300 Rum/30-378/300 wea, 7 rum/7 STW. I own a 375 Rum and it is definitely the king of the 375 bore, but at a great cost of powder, blast, recoil, throat erosion.
What are the overlooked calibers. In my opinion, all these "replaced" calibers. However with all the millions of great guns chambered for them they are going nowhere. I would bet many will be going strong when many of the replacements are rare, hard to find ammo and components, and no longer chambered by major manufacturers. Throw out a few of these underrated, 25-06, 6.5x55, 270 win,7x57, 30-06, and even the 300 WM. I am no doubt forgetting a dozen, but i doubt they will be forgotten or underrated to oblivion.