StormSurge, the 6.8 mm is easily retrofitted to existing Mk12’s and M4’s with only a barrel change and minor bolt modification so all the same lower receivers, upper receivers, bolt carriers, charging handles, optics, etc... can still be used. Also, the 6.8 mm uses a 28 rd magazine of exactly the same dimensions as the current M16 30 rd mag, so existing web gear and magazine pouches can continue to be used. In addition, muscle memory and years of training on the AR style weapons are not lost while transitioning to 6.8 mm. While I love 7.62 mm rifles using the 155 gr AMAX or 175 gr M118LR, the reality is that the 7.62 mm guns are bigger and heavier than an M4 (whether in 5.56 mm or 6.8 mm)--it is a lot easier to egress vehicles and clear rooms with an M4 than an M14 or FAL. It is also a lot easier to carry a full load of ammo in 28-30 rd M4 size mags than 20 rd M14 or FAL mags.