The original chamber has pressure issues with combat powered
loads. The SPEC II chamber helped a bit, and further testing
with different twist rate seem to have settled on something
in the 1:11 to 1:12 range for the smaller weight bullets
typical for this cartridge.
Today the best choices for the 6.8 SPC have settled on
the SPEC II, or DMR, chamber and a 1:11 or slower twist,
to get the most muzzle velocity out of this intermediate
sized case.
Squeeze
