6.8, does it do ANYTHING 7.62x39mm with a good brass case and attention to detail won't?

 Both are cartridges primarily designed for under 300 yds abd both fit in a conventional AR action.

 If you like 6.8 then more power to you.  I was just wondering.

As you can see below, the 6.8 out performs the 7.62X39 everywhere.  Both Loads below are Remington factory loads.

Ballistics Results
Back to Ammunition Ballistics

Cartridge Information
Index Number Cartridge Type Weight (grs.) Bullet Style Primer No. Ballistic Coefficient
R68R2 Remington® Express® 115 Metal Case 9 1/2 0.292
L762391 UMC® 123 Metal Case 7 1/2  


Velocity (ft/sec)
Cartridge Type Bullet Muzzle 100 200 300 400 500
Remington® Express® 115 MC 2625 2329 2053 1797 1565 1363
UMC® 123 MC 2365 2060 1780      


Energy (ft-lbs)
Cartridge Type Bullet Muzzle 100 200 300 400 500
Remington® Express® 115 MC 1759 1385 1076 825 625 474
UMC® 123 MC 1527 1159 865      


Short-Range Trajectory
Cartridge Type Bullet 50 100 150 200 250 300
Remington® Express® 115 MC 0.5 1.0 zero -2.9 -7.8 -15.1
UMC® 123 MC 0.1 zero -2.2 -6.8 -14.1 -24.5


Long-Range Trajectory
Cartridge Type Bullet 100 150 200 250 300 400 500
Remington® Express® 115 MC 2.5 2.1 zero -4.2 -10.6 -32.4 -68.3
UMC® 123 MC              


Note:  These ballistics reflected a test barrel length of 24" except those for 30 Carbine and 44 Remington Magnum which are 20" barrels.
 Specifications are nominal. Ballistics figures established in test barrels. Individual rifles may vary from test barrel results.
 “zero” indicates yardage at which rifle was sighted in.
* Inches above or below line of sight. Hold low for positive numbers, high for negative numbers.

Here is Remmys premium loads in both calibers, again factory ammo.

Cartridge Information
Index Number Cartridge Type Weight (grs.) Bullet Style Primer No. Ballistic Coefficient
RM68R1 Remington® Express® 115 Boat Tail Hollow Point Match 9 1/2 0.333
R762391 Remington® Express® 125 Pointed Soft Point 7 1/2 0.267


Velocity (ft/sec)
Cartridge Type Bullet Muzzle 100 200 300 400 500
Remington® Express® 115 BTHP Match 2625 2365 2119 1889 1676 1484
Remington® Express® 125 PSP 2365 2062 1783 1533 1320 1154


Energy (ft-lbs)
Cartridge Type Bullet Muzzle 100 200 300 400 500
Remington® Express® 115 BTHP Match 1759 1428 1147 911 717 562
Remington® Express® 125 PSP 1552 1180 882 652 483 370


Short-Range Trajectory
Cartridge Type Bullet 50 100 150 200 250 300
Remington® Express® 115 BTHP Match 0.5 1.0 zero -2.7 -7.4 -14.3
Remington® Express® 125 PSP 0.1 zero -2.2 -6.7 -14.0 -24.5


Long-Range Trajectory
Cartridge Type Bullet 100 150 200 250 300 400 500
Remington® Express® 115 BTHP Match 2.4 2.1 zero -4.0 -10.1 -30.1 -62.5
Remington® Express® 125 PSP 1.5 zero -3.8 -10.4 -20.1 -51.3 -102.5