Mid length or carbine 6.8 SPC ?

[chuck1024]

I'm a newbie to the 6.8 SPC, but it is the next upper that I buy, and soon. Should I get a carbine or midlength gas system?My searching was not successful... What are the pros and cons?

[68WJ]

Assuming a 16"-18" barrel, the gas port is moved closer to the muzzle and delays the moment that force is applied to the gas rings and unlocking occurs, thus allowing chamber pressure to be less and decrease the stress required to unlock and remove the spent case. There is a very minute difference though. Based on user reports, a carbine gassed gun isnt wrong, but a mid-gassed gun seems to operate smoother. Gas port diameter is also an unknown factor between barrels.

[snyderiii]

I will caveat this answer with, I've only built 5.56's... My next build is a 6.8, so everything I'm going to state is related to what I've learned dealing with the M4.

PRO's... the midlength is more reliable. At least that's the argument. Specifically, the theory is the mid length runs cooler and therefore cleaner.

If you are going with a pinned iron sight front gas block, thats the only REAL argument which is fact based, it should give you slightly better accuracy (assuming things like barrels are the same, etc). I've never seen any numbers completely prove to me the mid length is actually more reliable. Perhaps over the life of the steel (i.e. over your life, your sons life and his sons life... with each of you putting rounds through the same gun on a very consistent basis) you would see some higher reliability in a mid length over a carbine. But it really comes down to a lot of speculation because there haven't been enough true statistically valid experiments (that I've ever seen/read) to determine what that reliability actually equates to.

However, because noone argues that a middie is any worse and because it is (at LEAST theoretically) cooler and cleaner, why not just get the mid length. It's not like you will pay some ridiculously high price to go from a carbine to a mid length.

I have carbines and mid lengths... they all run well... they all need to be cleaned... they are all my FAVORITE.

[RUTGERS95]

personally, I'd like to see some studies done on the differences as what looks good in theory, isn't always how the real world works. I've use both in both 5.56 and 6.8 and see zero difference in performance. I think port diameter is more important but again, I'd like to see something in the form of a study etc...

[chasw]

I'm a newbie to the 6.8 SPC, but it is the next upper that I buy, and soon. Should I get a carbine or midlength gas system?My searching was not successful... What are the pros and cons?

Chuck: Take a que from the premium 6.8 barrel makers, mid-length is the best choice. You will be hard pressed to find any of them making barrels 16" or longer with anything but mid length gas ports. Carbine gas is for shorty barrels and that's about it. - CW

[Kentucky Jeff]

There are a ton of advantages to a mid-length gas system over a carbine length system and zero dis-advantages.

The practical advantages alone are sufficient to push one to use the mid-length system. If you want to use a rail go to the gun store and compare carbine length rails with mid length rails. Which one would be easier to grab with a light, sights, maybe a vertical grip, bipod etc all hanging off it. No contest. The mid-length system gives you more real-estate to hang accessories AND grip the stupid gun....

That doesn't even get into the improved reliability and softer cycling issues...

[Clint]

An quality upper from any of our forum sponsors is a good choice.

They provide optimum combinations of gas system lengths, port sizes and chambers.

[FloridaMutt]

POF made a good video on the subject. Obviously it was very biased but I drank the piston cool aid (and I'm very happy). Anyway, the video talked about the timing was too fast. Thus, failure to extracts (brass still pressured), failure to feeds (bolt running to fast for mag), etc. etc. If one buys into these ideas, why wouldn't one go ML? I think I've only seen one 6.8 barrel in carbine length. Even the shorty barrel I want is ML.

[t_ridl]

I guess I can give my opinion on this since my 6.8 is carbine length. I love my 6.8 but if I can buy it again I wished that I went with the mid-length system. I own a 5.56 in mid length as well. As what I can tell is that I don't feel much difference when its up against my shoulder. But I put a Tubbs Flatwire spring, a heaver buffer, and M-16 bolt carrier and I'm ejecting at 3:30 position. But I know that there is more pressure at the bolt gas rings so its going to wear faster but how much faster is the question. You can also take into consideration that the military has been using carbine gas system for how long and they still use it.

All in all, when I buy another barrel I will be going with a mid-length gas system to incease the life but I'm happy with my carbine.

[John A.]

My 5.56 and 6.8 16 inch M4 barrels are both carbine length.

I also have a pistol length on my 8.5" sbr 5.56 barrel.

I've had no problems with any of them.