In hindsight, I should add futher context to my previous posts.
The best condensed version of the gas ring's function (that I have read) is in
The L frame Story article by Mike Wood over at the Revolver Guy blog. "The gas ring's purpose is to prevent carbon and lead from building up between the axle ("arbor") and the cylinder itself, which would impede the rotation of the cylinder." One of the seemingly forgotten flaws of the original K frame Magnums is related to this. The extreme heat, and recoil, generated from firing Magnum rounds caused the gas ring to move foward and impede cylinder rotation. Massad Ayoob stated in the Sept./Oct. 1980 issue of
American Handgunner "The Combat Magnum is theoretically ideal for use in law enforcement. The only problem is that, especially in the stainless version, it is not unknown for the gas ring to move foward and bind the gun due to buffering from magnum recoil." Smith and Wesson were well aware of this and made a brief change that lasted from 1972 to 1977.
To try and mitigate this problem S&W moved the gas ring from the cylinder to the yoke on all K frames. This was VERY controversial, especially amongst police officers and competition shooters (obviously some overlap there). The yoke mounted gas ring did not seem to work as well as the cylinder mounted ones, and K frames of this era were well known to be very susceptible to sluggish cylinder rotation. It did not take nearly as many rounds down range to notice a difference. More material was also removed from the forcing cone, which made that well known problem even worse. Smith and Wesson went back to a cylinder mounted gas ring in 1977. Taking a look at a 67 no dash and a 67-1 will show the difference.
Fast foward to today. The new 19-9 and 66-8 revolvers have no gas rings at all. This was done to allow for a full sized forcing cone. One flaw was traded for another. I am sure that there are folks that have fired a million dirty handloads through their example without issue, but this will make them more prone to sluggish cylinder rotation than just about any S&W revolver ever produced. The Model 69 also has no gas ring. It makes no sense on that model, as S&W could have just went with a slightly shorter cylinder (like Taurus did on their mid size .44 Magnums). This is one of the things that make the new K frame Magnums a big no-go for me. Obviously, something like this would have never been tried during the revolver era in law enforcement. Honestly, I would rather have a clearanced forcing cone than a deleted gas ring.
The funny thing is that all of this can be avoided with a half lug L frame. The full lug barrel on most L frames make people think that they are bigger than they really are. Once again, there is less than one ounce of weight difference between a K frame Magnum, and a half lug L frame with the same barrel profile. The 620 and the 66-8 both have half lug, two-piece bull barrels. One weighs 37 ounces and the other weighs 36.9 ounces. A six shot 686 Mountain gun weighs 35.5 ounces, and the seven round version weighs even less. The L frames can also be had with a seven round cylinder that has offset cylinder notches. Even when you put the warts of the K Magnums aside, the half lug L frames still make far more sense.
Here are some good links and the aforementioned article
The Smith & Wesson L-Frame Story - RevolverGuy.Com
Jamming-Binding-Locking up new model
https://www.gunblast.com/SW619-620.htm
https://www.gunblast.com/SW-357MtnGun.htm
Gas ring yoke vs cylinder
