The .308x 1.5" Barnes was America's own 7.62x39. simply cutting a .308 cartridge down to 1.5". However Barnes offered only the brass, not any loadings, for wildcatters to play around with. The benchrest series of cartridges came from it and they are considered the second most accurate cartridges next to the PPC series. The two most popular benchrest rounds are .30 and 6mm.
6mm benchrest is close to the 6mm PPC having more power but being slightly less accurate under 300 yards.
>95 grains close to 3000 fps
>105-108 grains to 2900 fps
It's not much but it at one point held the world record for a 10 shot group at 100 yards measuring only 4.2"
http://www.6mmbr.com/page/page/1309618.htm
It has spawned a number of wildcats that attempt to improve on it like the 6mm Dasher and 6XC each trying to squeeze a little more performance out of the case. The Dasher then took the 1000 yard title grouping only 2.68"
http://bulletin.accurateshooter.com/2014/04/best-10-shot-1000-yard-group-in-history-be-amazed/
The .30 br is probably the closest we'll get to an American 7.62x39 style of cartridge
>112 - 125 grains run at 3000 fps out of 24" barrels with 20" barrels dropping ~40fps
These may be higher then 7.62x39 but the lack of taper and sharp help it along and if it was more suited for an assault rifle a drop of 200 fps could probably be seen due to greater taper and more gradual shoulders and another 100 from a drop to a 16 inch barrel most likely. In the benchrest world this cartridge has high praises, long barrel life (5000-7000 rounds for match grade accuracy), and bigger holes yields easier scoring.