Maybe I'm crazy but I swear I saw boxes of Federal Lake City manufactured Ball ammo in 5.56x51 at Bass Pro today. I double checked and all the other manufacturers were 5.56x45. I can't find it anywhere on the net so am I crazy? Is it a real cartridge, mislabeled, or I'm losing my mind?
Never heard if it but wouldn't be surprised, academy still has a lot of strange stuff sitting on the shelves from their efforts during the shortage. Seems they grabbed anything they could get their hands on including ammo that was made specifically for an MG with no civilian version.
Pretty sure you're crazy, but if not, I'd have picked up a box for the novelty. I've come close to grabbing a box of the 4.6mm they have on the shelf for just that reason.
"Cartridges of the World" doesn't list it and a search went poof. I saw the picture in your link site. Interesting but I wouldn't expect to find rifles chambered for it.
You should buy some. When I collected cartridges, some of that stuff was pretty valuable. Collectors like the odd and unusual cartridges.
Wow, this is an old one... Looking back, willing to bet that what the OP saw was just a screwed up label, even though there is an actual round with those measurements. IIRC it never even got past the R&D stage, or got booted out of testing early on.