Agreed. What the 6.5/6.8 should have been.
Personally, I'll take 6.5 as there are better bullets, so long as we are not confined to M16 magazines.
The ideal round should be relatively light vs.the 308, moderate body taper for good feeding, have goot short range killing power, and good moderate range petformance. Ideally, it shouyld also be effective at long range for DMRs and GPMGs. It should also have relatively low recoil for full auto use.
For my bullet I pick the 6.5 123gn Lapua Scenar with a BC of 0.547. I want the recoil under full auto to be controllable, so it must not be much more than the AK. We set our velocity target from an 18inch bbl for 2600fps. With a rifle weigh of about 9 pounds stripped, this gives us more recoil than the M16, an a touch more than the AK. Assuming a muzzle brake, this is reasonable recoil, even under full auto. The 6.5 grendel can manage 2400 with this bullet, so we will require a longer case to gain velocity and enough taper to ensure reliability.
How does the round compare with the current issue 5.56x45 and 7.62x51?
Recoil: The 6.5 has about half the recoil of the 7.62x41, and about 1.8x that of the 5.56.
Energy:
Code:
cartridge 0 100 200 300 400 500 600 700 800
M855 1239 1019 832 673 538 426 335 264 210
6.5 1846 1649 1469 1305 1155 1019 896 787 689
M80 2502 2145 1829 1551 1306 1094 912 758 631
the 6.5 proposed comes very close to 308 at moderate ranges, and overtakes it long range. This with a lighter bullet going slower
A second variation of the 6.5 using the 108gn Laupa scenar at 2800 fps yields slightly less recoil, about 1.5x that of the 223.
Code:
cartridge 0 100 200 300 400 500 600 700 800
M855 1239 1019 832 673 538 426 335 264 210
6.5 1880 1658 1458 1277 1114 968 838 722 621
M80 2502 2145 1829 1551 1306 1094 912 758 631
It seems that we can pretty easily create a cartridge that comes very close to 7.62x51 without the heavy weight or recoil of 308. Get the bullet to fragment like the M855 and M193, and it beats the 5.56 in every way.