Just guessing but......... I would say that a 12.5" 308Win would quite easily out preform a 20" 6.8SPCII in re to energy delivered to target animal. --- pruhdlr
Note: 7.62 NATO 147 gr at 2756 fps Barrel length unknown for spec, but 19-21" was my guess for the table below (my M1A is 21")
150 gr HPBT Win 748 loaded to a chamber pressure of 56.4K PSI WARM load 45 gr NOT a starting load. I chose 748 as the powder as it is most like NATO powder.
26" = 2918 FPS MP= 6.6K PSI –– 99.6 % powder burnt - 2836 ft/lbs
24" = 2873 FPS MP= 7.4K PSI –––––––––––––––––––––––––––– 2750 ft/lbs
22" = 2823 FPS MP= 8.2K PSI –––––––––––––––––––––––––––– 2655 ft/lbs
20" = 2766 FPS MP= 9.2K PSI –– 98.7 % powder burnt - 2548 ft/lbs
18" = 2700 FPS MP= 10.5K PSI –––––––––––––––––––––––––––– 2428 ft/lbs
16" = 2623 FPS MP= 12.0K PSI - 97% powder burnt –––– 2291 ft/lbs
14" = 2531 FPS MP= 14.0K PSI –––––––––––––––––––––––––– 2133 ft/lbs
12" = 2417 FPS MP= 16.7K PSI - 94% powder burnt –– 1946 ft/lbs
10" = 2273 FPS MP= 20.5K PSI –––––––––––––––––––––––––– 1721 ft/lbs
8.0"= 2080 FPS MP= 26.0K PSI - 87% powder burnt. - 1441 ft/lbs
6.0"= 1800 FPS MP= 34.1K PSI -79.4% powder burnt -1080 ft lbs