What buffer are you using in the 6.8 , shooting both tactical and regular loads…
Standard Carbine weight. I only shoot 115gr. OTM from SSA. I do not do more than double taps with it though. I’m sure an H buffer would work fine also.
The pressure curve on a 6.8 is not as long as a 5.56 due to the faster powders and case capacity to bore area ratio. With a .928 port in the mid gas location you can use carbine or rifle buffers but, enidine and most heavy buffers cause short stroking especially with light 90gr bullets or Hornady or Remington ammo.
Rifle port locations with a 20" barrel really causes problems if you don’t load near max charges.
ETA some barrels are over gassed, the port should not be .100 or more on a mid or rifle gas system. carbine gas systems are hard on the bolt and carrier and should not be larger than .800.
My 6.8spc 12.5" Noveske barreled carbine will not catch the bolt on the last shot if I use my hydraulic buffer. I shoot mostly 115 FMJ’s for practice.
That said it works just fine with an H or an H2 buffer. My barrel has a carbine length gas block … not mid-length.
openbolt
My LWRC came with a H2, never felt a reason to change it.
I’m running a MGI buffer with uncut SSS flatwire spring in a Stag 6.8 upper. It has a carbine gas port, and will lock the bolt back when empty with even light handloads or SSA 110 PH commercial loads.
Ok, I called Noveske last week after I posted and they recommend using an H2 buffer with the 6.8 in a carbine.
openbolt
I have a RRA Midlength on the way. I hope a standard buffer is GTG.
I am running a H buffer in my LMT MRP 16 inch. I changed from a standard carbine buffer and it changed the angle of ejection from around 2:00 o’clock to around 3:30. I am surmising that it slowed the speed that the bolt was traveling rearward just a little.
IPSC_GUY
SIERRA II ALPHA
I have a 16" lightweight, mid-length tube purchased from Tim @ Kotonics. I found my set-up runs best with a H3 buffer. This was after trial and error with C, H, and H2 buffers. It plants the brass most consistently at the 3 to 4 o’clock position with the widest range of factory and hand loads (including SSA tactical loads). YMMV