the original model 19 was a derivative of the k frame model 15 chambered for 357 magnum instead of 38 special. this allowed the use of 357 magnum in a k frame gun instead of the n frame which some patrol officers and bill Jordan felt was too heavy. it was wildly popular. it was the glock 19 of the 60's and 70's. however, a great deal of the population of law enforcement officers that carried a 19, shot mostly 38 special with it and may or may not have carried 357. for range practice, qualifying, and for some officers on patrol, 38 special remained the most popular option. that changed dramatically after the 1970 Newhall shooting where 4 chp officers were killed. without further analysis of that incident here, one of the outcomes was a determination for the need to practice and qualify with the same cartridge type that officers carried. while some departments went back to the 38 special exclusively, for good reasons, others adopted the 357 for all purposes. this created a situation where a large population of model 19's was now experiencing a high round count of 357 that far fewer individuals subjected them to previously. many model 19's survived a great deal of 357 use, but some failed.
the failures occured where the barrel face and forcing cone were relieved to make room for the ejector rod. this is the flat spot you referred to. the reason it's there is to allow for a fat ejector rod to fit under the barrel in a relatively small frame. the frame window of a k frame is small. that's what makes it compact, lightweight, and keeps the bore axis low. but with limited height in the frame window, smith and Wesson had to fit half the diameter of the ejector rod and the whole diameter barrel into the radius of the cylinder or half the height of the frame window. that is just how a da revolver works. if they made the barrel thick, the ejector rod would have to be thin. if they made the ejector rod thick, the barrel would have to be thin. the flat spot is an attempt to compromise. it worked wonderfully for 38 special in the model 10, and model 15 and for many decades. it worked very well for the model 19 too until lots of people starting shooting a high volume of 357. the reason smith and Wesson didn't make the barrel thick and the ejector rod thin is the ejector rod is one of the two things that holds the cylinder in place. the other thing is the cylinder stop that mostly serves to lock the cylinder and keep it from rotating. so the ejector rod is pretty important to holding the cylinder firmly when the gun is fired. smith and Wesson had a good reason to relieve some of the underside of the barrel to allow for a thicker ejector rod.
how to solve this problem; initially, the problem was solved with the l-frame. the solution was very simple but elaborate as well. the simplicity of the solution was to simply make the whole frame a little taller to fit a thick barrel and thick ejector rod both into the frame. what is elaborate about this is that it required a whole new frame forging and new cylinder, in-between the k frame and the n frame. the l-frame was introduced in 1980 and this solved the problem for police agencies that had adopted the practice of firing high volumes of 357 through their service revolvers. for most individuals, there was never really a widespread problem but certainly some did experience cracked forcing cones and this as was pointed out was not unique to smith and Wesson but happened to other guns as well. rugers speed six / security six line was discontinued and replaced with the gp100 for the very same reason, though the propensity for ruger s/six line revolvers to experience this issue does not get nearly as much attention whereas the smith and wessons reputation seems to be remembered by everybody that wasn't even alive back then.
more recently smith and Wesson reintroduced the k frame model 19 and 66 with a different but not a new solution. remember the dilemma was that they wanted both a fat barrel and a fat ejector rod, the latter due to the fact that the cylinder was held in place during lockup by that rod. the alternative is to hold the cylinder in place using a detent on the crane, also known as the yoke. with the yoke locking the cylinder to the frame instead of the ejector rod, the ejector rod can be thin. this is exactly how the gp100 works. take a look at the gp100 and notice how skinny the ejector rod is. that is because there is a detent on the yoke rather than on the end of the ejector rod. notice how on most smith and Wesson revolvers, the ejector rod locks on a detent at the rod's end. this arrangement favors a thick, stiff ejector rod. notice that on the gp100 and the new model 66 and 19 the ejector rod is skinny and the end of it free-floats in the barrel lug. ruger was not the first to use a detent on the yoke, however. dan Wesson revolvers also have this feature and it seems that the gp100 was inspired by the dan wesson in several ways. the first to use yoke detents as actually smith and Wesson with their 'triple lock' design of 1908
https://en.wikipedia.org/wiki/Smith_&_Wesson_Triple_Lock the us army requested the feature be deleted, but gunsmiths have been installing 'ball detents' on revolver yokes as a custom feature ever since. here is a gunsmith advertising the service;
https://cylinder-slide.com/Item/CSM907 having a detent on the yoke of a revolver that also locks on the end of the ejector rod is like having a belt AND suspenders.
so the new model 19 and 66 do not have the area under the barrel face and forcing cone that has been thinned or flattened because they use a yoke detent and a slimmer ejector rod. they will, in theory, be more durable than the older model 19's. everyone's experience is unique though and lots of people had and continue to enjoy old model 19s without any problems, and no doubt there is someone out there who broke a new model 19.
consider that the j frame fits the same bore barrel and an ejector rod supported cylinder in an even smaller frame window. albeit the jframe cylinder is smaller and therefore does not need as stout of a rod to support it, but the j frame forcing cone is still thin for sure. you don't read nearly as many complaints about it though. perhaps some of that is because few people shoot a high volume of 357 through a j frame, but then nowadays few people shoot a high volume of 357 through old model 19's. what people do continue to do is borrow revelation in knowledge from others without any first-hand experience.
if you want an old pinned and recessed model 19 with goncalo alves stocks, there is no modern gun that is a substitute. if you just want a nice 357 revolver to shoot, the new model 19 and the new model 66 even more so are easily the best k frame design smith has ever produced. it is a superior design, as is the sleeved barrel and the mim production method assures much better consistency in a number of the revolver's components.
I would also add that many people found that the k frame was never suited to shooting 357 for reasons other than the gun's durability. there is a good reason that most law enforcement agencies responded to the outcome of the Newhall incident by standardizing their ammunition for practice, qualifying, and patrol, and they standardized on the .38 special rather than the 357. these departments never learned about the model 19's weakness because they continued to use 38 special. shooting 357 in a k frame is similar to shooting 357 in a j frame. you can do it, but a lot of people find that it is not what they want to do. the l-frame 586/686 and the gp100 solved more than just the cracked forcing cone problem. they gave the 357 platform a great deal more heft with a full underlug barrel and a more massive cylinder and frame. notice that the gp100 adopted the yoke detent way back in 1985 and therefore it could have kept the smaller s/six series frame size and beat smith and wesson to their new-model 19/66 by 29 years - the new 66 with yoke detent was introduced in 2014. but ruger enlarged the gp100 to a similar size and mass as the 586/686 in spite of perhaps not needing to because of that detent. the reason they did this is because if you really want to shoot a high volume of 357, you want a gun with the mass of an l-frame or gp100 or a dan Wesson or maybe a new python. a desire to shoot a high volume of 357 through a k frame isn't much different than a desire to shoot a lot of 357 through a j frame. its not what a lot of experienced men set out to do.
now supposing you do get an l-frame to consume that big diet of magnums. you'll probably also want a government agency to pay for the big diet. if you spent your entire stimulus check on 357 and shot it all, you would not likely get even close to harming a j frame or an old k frame with the flat spot. so if that's all you have for government support, you better dig deep into your savings if you expect to punish any revolver.
