Unfortunately, this is a rather common problem with 6.8 Contenders(I know there are those that are overjoyed with their results and I'm truely happy for them...BUT, there are many who aren't too.)
My long time huntin'/shootin'/fishin'/drinkin' buddy bought two 6.8 carbines(one for each grandson). Both miss-fired miserably. He had MUCH disscusion w/ Hornady and TC. Hornady sent new ammo and TC sent a whole box full of new parts which I installed for him. The new ammo didn't help but, so far, the new parts(knock, knock, knock)haved cured the problem on both guns. The parts included new firing pin, bushing and spring, and new hammer spring. Also included was a little washer that fit over the end of the hammer spring(in effect lengthening the spring). The tech/rep said the washer was not a TC part or reccomended factory procedure, but was his personal suggestion. In hind sight, I wish I had tried the washer "trick" just by itself first. Both carbines were G-2's.
Walt