I believe that what you are seeing is the effect of Bore Transit recoil. On any handgun that places the barrel above the axis of the wrist, there will always be some degree of muzzle rise while the bullet is transitting the barrel. The amount of of this rotation of the gun is dependent on 4 factors, the distance the barrel is offset from the axis of the wrist, how well the shooter controls the rotation of the gun during recoil, the power level of the recoil, and the "dwell time" of the bullet in the barrel.
Offset of the barrel form the wrist axis is dependent to a large extent on the particulars of the design of the handgun. About all that can be done about this is taking as high a grip on the gun as is safe, other than that, it is what it is.
Control of the recoil, or follow through, is one of the greatest challenges in becoming consitent with shooting a handgun. IMO, the only answer to this is Practice, and lots of it. However, the grip can also have a huge influence in how well the recoil can be controlled and the effect of follow through increases in proprtion to recoil, which means that shooting lots of light caliber loads won't do as much for your shooting with a major caliber as most seem to think. I have found for me that best grip is the largest grip that permits a comfortable "reach" to the trigger and enough "traction" that the grip doesn't shift in my had during recoil. That means that all of my handguns with interchangeable grips are equipped with rubber grips. I've also found that as recoil increases, I'll give up a bit on a shorter trigger reach in order to have the benefit of a covered backstrap and a grip with more surface area for traction. On my 4 inch 620, the only grip I use is the 500 Magnum Monogrip from S&W's store, nothing else I've used affords the degree of control that this grip offers for the 357 Magnum. Since it's only about 65 dollars, I would suggest that you purchase one and give it a try.
While that big rubber grip won't be nearly as pretty as wood, it will allow a LOT more comfort when shooting 357 Magnums and a much higher degree of control. BTW, I do NOT believe that the 357 Magnum is a good choice for a carry ammunition. I have found it difficult to group well with in rapid fire drills with the 357 Magnum and it's my belief that getting good hits on target is a lot more important than missing on followups with a more powerful caliber. If I were to carry a 38/357, my carry ammo would be a quality 38 spl. defense round, not the 357 Magnum. So, if that large rubber grip is an issue for carry, just mount a nice boot grip you can shoot well with using the 38 spl. and use that as your carry combination.
Now a word on barrel length. I have a 6 1/2 inch model 610 and have found that this gun is VERY sensitive to recoil management. This may seem counter to intuition until you consider just how much time the bullet spends traveling through that long heavy barrel. That long transit time means that it takes a lot more attention to form for me to shoot it well than any of my shorter barreled handguns. So, once you find a grip that works well onn your 686, you'll probably find it fairly easy to shoot will with. It will still shoot high with the Magnums but that's normal. With my 4 inch 620, going to Magnums just requires me to use a 6 o'clock hold on a 3 inch bulleye at 30 feet instead of a Combat hold for the 38 spl.
Finally, a note on bullet weight. For a given power level, a heavier bullet will tend to shoot higher than a lighter bullet at the same power level. The reason is that the heavier bullet is moving slower and that means that the transit time increases. More time in the barrel means thee barrel will rise a bit more when the bullet leaves the end of the barrel. So, once you've chosen a spedific bullet weight you want to "specialize" in, sight the gun for that weight and alter your sight picture when shooting bullets of a different weight.
