Let's look at a bit of handgun history. Back in the early 1930's, Phil Sharpe, along with Elmer Keith and others helped develop a .38 Spl. load called the 38/44. This round shot a 158 gr. bullet at around 1150 FPS, if memory serves. It was to be used only in S&W heavy duty 38/44 revolvers built on the "N" frame. I had one of the 38/44 "Outdoorsman" revolvers and loaded it up with Hercules #2400 powder with the 158 gr. Semi-wadcutter Keith style bullet. It was a real killer, and I used it on a Black Bear with no problem. The round was discontinued, because it could be used in regual frmed .38's and in revolvers chambered for the .38 Colt round. (BTW. those old .38 Colt's will also chamber a .357 Mag. round with disasterous results.)So the round was lengthened about 1/10 inch and called the .357 magnum. The 38/44 revolvers were made until at least 1959 (according to an old Stoeger's catalog I have, and were fine guns.) I sold the one I had years ago, but have since aquirred another that is definitely not for sale.
Although the 686 S&W is made to handle .357 Mag. ammo, current factory ammo is greatly reduced from the original 1935 specs. (1200 to 1300 FPS vs 1550 FPS) I still load my .357 ammo to duplicate the 1935 loads, but I do not recommend them in a 686. I use "N" frame guns for those loads, and those sparingly.
If you want to try .357 class loads in .38 Spl. brass, find an early Lyman reloading manual that has .38 Spl. High Velocity load data. be aware though, that when they mention #2400 powder, they are using the Hercules version, and not Alliant. With Alliant #2400, I have had to reduce .44 mag. loads by 2.0 gr. and .357 Mag. loads by 1.5 to 2.0 gr. Just a word to the wise.
Paul B.