Here is my take on it. The diameter is wide enough (.357") that you are no longer totally dependent on the round expanding, which means that it does not expand when it hits small game so it doesn't tear up much meat, while at the same time, that same bullet can and usually does expand when it hits something bigger like a deer, hog, or 2 legged threat, while still penetrating enough to easily get the job done on any of the above. It is big enough that you are no longer having to wonder if you have enough gun, but at the same time still small enough that recoil is very controllable to the point of not being a concern at all in a rifle, or (for most adults) in a handgun either. As to the accuracy of it, I can't answer that one, but I think part of that is due to the long history and unbelievable amount of load development that has gone into the .38/.357 over the decades. With my .357 rifle, I regularly get 1.5-3" groups at 100yds, and the accuracy and power are sufficient that I trust the rifle out to 150yds on deer/hogs. Some people limit this round to 100yds or less, some give it more than I do and say it is good to beyond my 150yd limit. The way I see it is that this is a round that depends on precise placement but is very capable within the ranges most people limit it to. It will never be a long range round with performance like a .308 or a .30-06, but at least for my hunting needs in my area which offers few shots over 100yds, it works great. I'm not saying that I will ever replace the longer range capable rifles with pistol caliber carbines, but most days, I would much rather hunt than just shoot--and the .357 lever gun is one of my favorites.
