Talked to a guy today at MSAR, and they are coming out with a new version of the STG soon. It will accept the AR magazines, and will be called the "E4". The 6.8SPC barrel specs were dictated by SSA's standard requirement for their ammo since MSAR felt they lead the industry in terms of 6.8SPC ammo. Barrels are going to be SPC II, 1:11 twist (I forgot to ask how many grooves). The only difference for the left handed bolts on these are the angle that is drilled into the cam head bolt. You will have the option of purchasing either the rifle in 6.8SPC configuration, or a barrel and bolt as an upgrade if you have the 5.56. He said its VERY fast to change out. I thought it was interesting that they did this change over to accept AR mags because the 6.8 gave them issues with a composite mag. Personally don't like the price tag on these, but I was checking one out this past weekend at a show and for as awkward as it looks, its actually fairly comfortable to shoulder. I like how compact it is while keeping a 16" barrel. I'ld like to try playing with one in a vehicle to see how well she swings...