We've Missed the Boat By Not Making 6x45 The Primary AR15 Cartridge

[Robert]

There is a 6.8x45...

 

[barnbwt]

There is a 6.8x45...

Really? Gosh, that's like a whole other three-quarters of a millimeter! Gonna be bringing down Elk, Moose, Polar Bears, and airliners with that one!

Is it anything but an SPC de-tuned so as to fit in AR bolts/magazines? Looks like it'd have to be darn near identical (down to the stubby low-BC bullets). Probably a nice-to-have for SBRs, I guess

 

[Mosin Bubba]

Geez, so serious, and in a silly caliber-war thread, to boot (oh wait, that you started, my bad )

You do realize that the difference between ANY 6mm-6.8mm cartridge that'll fit in an M4 is exactly moot, compared to the performance of either 5.56 or >30 caliber options, yes? And even then they aren't super huge differences inside of hundreds of yards. Therefore the minute differences between them will be either marginal or subjective (set by personal biases or preferences, such as my favor for high BC projectiles and low aspect ratio bottleneck cartridges)

This.

If you want your round to fit in an AR-15 magwell and feed from a double-stack magazine, you're basically forced to end up with a 223-sized cartridge. So you're going to get 223-level performance no matter what you do, because there's just not enough room for bullets or powder to make much of a difference.

It really only shows up when you try to min-max your cartridge to some extreme, like with the Grendel for long range or the Blackout for the biggest bullet a 223 case can hold. And there's not even that much of a difference between those rounds and a 223 until you start getting to the edge of the cartridge's effectiveness.

So say the 6x40 has 20 grains on the 5.56. What real-world difference does that make?

Really? Gosh, that's like a whole other three-quarters of a millimeter! Gonna be bringing down Elk, Moose, Polar Bears, and airliners with that one!

I love caliber wars.

 

[denton]

Show me a .30-30 load that can keep it's bullet within the manufacturer's intended operating window at 350 yards, and we can talk.

150 grain Hornady SST over a load of LeveRevolution, out of my Savage bolt action, 2512 FPS at the muzzle and 1814 FPS at 350 yards. 1800 is the bottom end of the bullet's operating range.

Sorry. Couldn't resist the challenge.

Now back to the serious discussion.

 

[Phaedrus/69]

I suppose there will always be a compromise so long as one rifle is expected to do virtually every job save a few special purposes. Especially since we always plan to win the last war instead of the next one. In Vietnam there was little use for the 7.62 outside of sniper/DMR use. Perhaps it seemed like the future of warfare would be suppressing fire and shorter ranges. Until Desert Storm came along!

It's probably true that unless we adopt a brand new rifle there's not much point to fretting overmuch about the caliber. A slightly larger diameter bullet would do some things better, some things poorer and most things about the same. Since the rank and file troops will be stuck with FMJ ammo it's unlikely adding a half a mm in diameter will turn a poodle shooter into Thor's hammer.

Personally I don't see enough upside to change now. True, had we went with something else 50 years ago as the OP said...but that ship has sailed. It would be like divorcing your wife and marrying her sister!

But if we were gonna scrap a billion rounds of ammo and buy five million new barrels, I could see a 7x45 or .300 AAC Blackout being a viable alternative to the 5.56x45.

 

[Al Thompson]

Looks like this one is done.......