I know, it's another caliber, and the US Army don't do knew calibers, ever since they insisted on making the M-1 Garand a 30-06 to use up warehouses full of that caliber. (The Garand was designed to shoot a 6.5 and hold ten rounds, I believe.)
"NOT A 6.5 Creedmore above, and that is a 1X4 Elcan."
Pretty close. The early Pedersen and Garand prototype semiautos were both 10-round rifles in the .276 Pedersen caliber, Pedersen maybe being a somewhat more knowledgeable ballistician than John C. Garand, a true mechanical engineering genius with better ideas regarding manufacturing techniques, important as wartime mobilization took place. Nowadays, we'd likely call the .276 Pedersen a 6.8mm, and the Remington 6.8mm SPC cartridge is the Pedersen round's great grandchild.
That odd pregnant-appearing swell of the Garand's stock at the area of the magazine housing that gives the Garand it's unique feel when grasped at the point of balance is the result of the enlargement of the clip and feed mechanism from a very trim 10-round .276 to a bulkier eight-round .30-06. The rest is history.
I know, it's another caliber, and the US Army don't do knew calibers
Well, SOCOM came up with the 6,8SPC, and that had a lot of promise when the XM-8 and SCAR were candidates for general adoption to replace the M16/M4. The 6.8 had problems when used in the M249 SAW, though, and is probably doomed to extinction. The .30 Blackout has been happily adopted by SF in its place instead, very capable of both close-in work with short barrels and also usable at longer distances with heavy .308 bullets. I'm reliably told that not only have there been some 4K enemy casualties from the .30BO, but that there's a nice pool and special trinket for the shooter who pulls the trigger on number 5K. I've not heard if they've worked up a M249 barrel in .30BO yet, but I sure wouldn't be surprised, and links wouldn't be a problem.