Quoted:
Longer gas systems provide less gas impulse and longer dwell times which places the recoil system in motion, more smoothly.

Traditional gas systems were carbine (16" and shorter barrels) and rifle (longer than 16") all with varying gas port sizes to accommodate the dwell time of the length of barrel beyond the gas port.

Mid-length became popular for allowing a software shooting 16" barrel, which is the most common length for civilians.

For a 16" barrel - get a mid-length.
For a 18" barrel - get a rifle or mid-length.  I have both in the same exact barrel from WOA and I cannot tell much difference.  Both are just as reliable.

Why are so many systems that are 16in built with a carbine gas system?

I can see it with shorter barrels but it seems there are just as many 16in barrels with carbine as there are with mid-length.

Is this because 16in barrels are to short for a rifle gas system and when they went to M4's they created a carbine gas system.
Then the mid-length commercially desgined gas system came out but many just kept building 16in barels in carbine length?

Are rifle and carbine lenght milspec and mid-length not?

Finally, considering a milspec weight bolt and milspec tension carbine buffer spring what weight buffer would you have to use to make a carbine length gas system act like a mid-length gas system?

Quoted:


Because the original "carbines" built by colt in the mid 60's varied from 10" to 16" barrel lengths, sharing a common gas system length - which became the carbine length.  This just stuck as it worked well with the 14.5" barrel, and worked with common hand guards, accessories, across those barrel lengths.  It made sense to use these in civilian 16" barrel lengths.  There were prototype "intermediate" gas system lengths developed by Colt in the mid 60's as well, and for whatever reason they did not take hold.

There was a rapid succession of M16 carbines by colt -

R605 (basically a "dissipater" using a rifle gas but 15-16" barrel)
R607-R610 (10" barrel, 7" gas system)  The R609 essentially became the XM177E1
R651/652 (14.5" barrel and 7" gas system)
These eventually led to the M4/M4A1.

The 14.5" barrel with 7" gas system had nearly the same dwell time as the 20" rifles commonly in use.  Just had a higher impulse due to being closer to the bolt carrier, and less volume in the gas tube.



The reason it was common in 16" barrels, is because the civilian market had a 16" barrel requirement due to the NFA, so they simply used all the same parts, just used a slightly longer barrel and adjusted gas port sizing to match impulse.



No.

See above.  You can make a 15-16" barrel work with rifle gas system, it just isn't as reliable due to lack of dwell time (bullet time in the bore beyond gas port)
They created the 7" gas system LONG before the M4 was a twinkle in someone's eye.



One could say that, certainly based on current milspecs for the M16A2, M16A4, M4, M4A1 mil specs.  It doesn't mean that there aren't some intermediate length customized systems deployed in specific roles, but they aren't current standard infantry configurations.



You cannot just "add weight" and make all things equal.  Adding reciprocal mass changes things like cyclic rate, felt recoil, bolt bounce, etc.  In general, it has become more popular to add reciprocal weight using M16 carriers and H/H2/H3 buffers to carbines with VERY short barrels, because they have larger gas ports resulting in much higher impuls, and cause unlocking of the bolt to occur while there is still significant pressure in the barrel/chamber.

Quoted:
The reason that the vast majority of 16" guns are carbine gas is because a) it's Mil-Spec and b) natural progression to as previously stated, Mil-Spec 14.5" carbine to 16" civilian legal length (w/o permed hider).

Oddly, someone just "went off" on a popular/major manufacturer in a thread just hours ago...because they could not tell him which buffer to run.  My answer was:  it's subjective.  Your gun is probably going to run with virtually any correct (carbine vs. rifle) buffer.  Subjectively, you may feel like one buffer is better than another, but, all else in spec/not worn, the gun probably isn't going to care.

Some people swear by the middy; others, like myself, and as previously stated above, don't really notice a difference.  So you're asking which buffer (actually range of buffer weights) would make a carbine feel like a middy when it's hard for some of us to notice a big difference to begin with.  See the dilemma?

Also, in the "madness" to tweak buffers, what is often forgotten is the trade off with the action spring.  Heavier buffers may require a heavier action spring...or will at least require replacement of the action spring sooner (due to wear and why I said all else Mil-Spec and not worn above).