Solid Answer: 0
6x45 (6mm-223) ?
Whatever happened to the 6x45? why did it fall out of favor? I assume it just got over shadowed by the old "tried 'n true" cartridges and fit in a very narrow gap, but I'm seriously considering building one in an AR platform as soon as I finish up the bench rest build I'm working on now...It seems it has a lot going for it; tons of 223 brass avail for resizing, can shoot a little heavier bullet than 223 at the same speed as 223 shoots 55 gr for better terminal performance downrange and its a very accurate cartridge...I'm not saying its better than the 223 Rem/ 5.56 NATO, just wondering why it never really took off. Maybe I just have a soft spot for these type cartridges, but then again, I usually bring home the dog nobody else wanted at the animal shelter...LOL
I've never built a 6x45 but some of what you said is true. If your just staying with the AR-15 platform there some calibers with better ballistics, 6mm BR/Dasher, 6.5 Grendel, 6.8 SPC unfortunately they don't use .223 brass so the cost savings are lost. All of my builds have been .223/5.56 and when I wanted something a bit more I went with the AR-10/DPMS .308 platform.
USS NOA DD-841
Lean, Clean and Mean
I have a 6x6.8 barrel I snatched up at a gun show and have ideas running through my head for it later on..A light just came on the other day while I was thinking about 6mm and I wondered what happened to the 6x45. Not that I've ever shot out a barrel on any of the calibers that I've owned, but now that I have more time on my hands and shoot way more than I used to, barrel life has become a factor in my decision making. That leads me back to the 6x45. A lot of guys over on the "predator forum" really like it. It's an oddity in that you don't find folks that hate it, seems everybody that shoots it or has shot it, likes it. Which is rare these days, usually the haters get in line to bash cartridges..Anyway, just something I'm kicking around in my head for something that will be easy & cheap to load/shoot a lot, and be a little different than what you see everyday.