Case volume on the two is very close. The LBC can be run with longer bullets thanks to the shorter case. It also can take a tad higher pressure.
The 6X68 as BHW is making was thought of a as a varmint/light big game round that would be a step up from the 6X45. The throat is short on this reamer and with the right magazines you can reach the lands without any problem.
The 243 LBC was also a varmint round but was recognized quickly as one that would make an excellent deer/hog cartridge and longer range platform. Velocities, I believe can be a bit higher with the LBC thanks to more eefciet case design. Short, fat is wher its at.
I now own, or will after next week, a 24" BHW upper in 6X45, 6X68 and 243 LBC. Needless to say there will be another OK Coral in Arizona when I'm done. I'll use the same bullets, 58 VMAX, 70 Speer TNT and the 87 VMAX and the 85 Game King. I want to see what top end velocities and pressures will be and how the accuracy hangs together. All three are 1:9 so that will be as straight across as I can get.
Group Buy is really a Group Special. Merely go over to the BHW Forum and all the info is there.
The site shows only a 20" satin but they have opened it up to 18", 20" and 24". Threaded or not. Black, satin or machine finish. (No bull barrels)
They are selling the uppers with 100 rounds of factory ammunition with a 150 round option that is cheaper than the componets to load it with.
Greg