From a lot of things I've read, it seems rifle length is the ideal gas system for 16".  If that is the case, why is it that almost every 16" on the market is mid-length?

why is rifle length gas ideal?  if need be i guess you could buy a 20" and have ADCO or someone cut it for you.

Mid-length is fine on a 16" barrel.

I don't know why it's ideal, which is why I asked.

KAC did rifle length on their's, and it was said over and over on sniper's hide a couple years ago.

SR-25's run well with or without a can, partly due to the gas length, also partly doe to the design of the gas block and a few other internals.
KAC put in a lot of hours designing rifles to a certain spec, which why they cost so much.

For the average guy who might go target shoot and plug a whitetail once a year the gas system isn't really much to bang your head at, but if you want the best their is something to be said about the rifle length on an SR-25.
I own one and it has run flawlessly over the 7000 rounds I've run through it, both suppressed and unsuppressed with every type of ammo you can think of..

To gas them hard so they will function with a wide variety of ammunition.  Most of the 16" guns on the market are actually CLGS, which is a big blunder in my opinion.  That is from the shear volume of AP4 and Oracle carbines out there.  I suspect that decision was made based on available furniture, not any kind of study of the pressure curve of the .308 Winchester and 7.62x51 NATO.

Keep in mind that Knight's has done untold numbers of hours on RDT&E to get the correct gas port size, correct reamer for the chamber, barrel steel, BCG components (extractor, ejector, springs, pins, chrome plating), recoil system, etc.

They have the most extensive and comprehensive collection of tool room samples and prototypes from Eugene Stoner's work at both Fairchild Armalite, as well as Cadillac-Gage.  They also have engineering staff, high speed camera, FES, and other professional methods for developing a weapon system that Billy Bob's machine shop does not, and never will.

I'm not a KAC fanboy, just someone who has watched this industry for a long time, owned enough of the different AR10 variants, and can sift through a lot of the clutter to see clearly.  Look at where the LMT MWS gas port location is, for example (RLGS).  How many threads do we see here where people are complaining about their MWS choking and coughing?

Fulton Armory uses RLGS on their 16.5" and 18.5" barrels, and they offer very accurate pipes for a great price.

If I were to spin my wheels backwards and get back into .308 AR's, I would spec the gun around a specific set of ammunition requirements.  For me, that would be some type of target and hunting bullet selection, mainly 155gr and 175gr SMK's, 178gr A-MAX's, 150gr & 165gr GMX's, 165gr SST, and 150gr Barnes TSX.  Since I got out of .308 years ago, it all seems like a waste of time looking back at it, especially when I see the BC's, think about the recoil, gun weight, etc.

Many of you will ignore that because of the .308's popularity, and it covers your needs just fine, and I understand that, hence my recommendations for those that are married to it.  Just like my AR15 builds though, I think it makes a lot of sense to source ammo that will run your gas system optimally.  I prefer M193, M855, 68gr/69gr/75gr/77gr HPBT for my 5.56/.223 Wylde guns, because they run extremely well on that diet.  When I was shooting .308 for target work, I used 155gr Scenar hand loads going really fast, nothing else.

A 16" rifle gassed .308 is a pleasure to shoot compared to a middy of the same length. I have had zero problems with mine, and that includes weak surplus to the good stuff. Much smoother recoil impulse than the mid.

I chopped my 20" barrel to 17" and didn't do anything to the gas port. It runs much smoother and shows ejector swipes much less.

IMO, .308's in general run better with longer gas systems than the AR-15. I wish there was a extended rifle gas system for 20"-22" barrels.

I am interested in getting a new barrel for my (originally) carbine length .308 DPMS Frankenbeast.

The gun only runs reliably if I feed it one specific load and only if I use a Magpul magazine.  The carbine length gas system is a significant part of the problem.

I want to try a full length or mid length gas system but I don't want to add a lot of weight.  The Fulton Armory 18.5" lightweight barrel may fit the bill.

I am not sure as to the quality but CMMG makes .308 barrels with what I would consider correct gas lengths.

I used one of the Fulton 18.5in LW chrome lined barrels with rifle length gas system on my .308 build.  I'm happy to report I've had ZERO malfunctions with the rifle (actually 1 but it does not count see below) but have only fired about 50 rounds and nothing past about 50 yards so no real accuracy report to speak of.  

Additionally I used an SLR adjustable gas block and running 7.62X51 ammo started with it full open then dialed it in almost 9 click before I had the first short stroke.  Backed it up 2 clicks and no problems.  

When I went looking for an 18in barrel a few months back it seemed like there were lots of them with mid length gas but very few in full rifle length.  As an M1/M1A guy I can't quite wrap my head around the diameter of most AR-308  barrels and the Fulton profile  was about at close to what I really wanted that I could find.

Years ago I bought one of the overrun 18" AR10T barrels Armalite did for the DEA if I remember right. Unfortunately my lazy ass never put it together but several who bought at the same time said they were very soft shooting.