I took my 686 to the range today to fire some .38 hand loads, which were probably +p since I was using a 158 grain hollow point and a starting load for a 125 grain. More recoil than same loading using a 125 grain, but not as much as a .357.

At 50 yards firing supported with a red dot, I was all over the place (approx 6 inch groups). When I fired some milder loads, the groups tightened up to a little more than an inch.

Is this to be expected? My 686 (6 inch barrel) has had trigger work done and I was firing single action. Up till now have been shooting from a Weaver stance at 50 feet or so and groups seemed decent for that type of shooting (but using light target loads).

If you want to test your concentration, try some 158gr .357 magnum hunting loads. Don't forget eye and ear protection.

The blast and recoil often bring out grip and trigger control issues.

Next time at the range I am going to place some padding between the rest and the barrel of the 686. I wonder if the recoil is allowing a slight movement in the barrel prior to the round leaving the barrel?

That would explain the tighter groups achieved when using a milder load with less recoil.

Resting the barrel is problematic. Barrels vibrate and bounce the gun away from a surface.
When shooting from sandbags, I take a proper grip amd rest my hands on the sandbags.

If the butt of the gun is interrupted in recoil, oftentimes one gets vertical stringing. Wanking the trigger will do it, too!

You might just have a lousy load. That's why you try varying powder charges. I call it the hour glass effect. As you start with a light load and work your way up the groups typically shrink (all else being equal) and then hit a point at which the groups start opening up. I've only had one gun that didn't follow this pattern and it was still shrinking the groups when I hit max load. Try some different load and see what happens. Good luck.

I believe that long barreled handguns are more sensitive to recoil management than short barreled handguns. If you think about it, the time the bullet spends in the barrel is longer than it would be in a short barrel. So, any variation in controlling the recoil will result in a larger grouping.

BTW, I base this on my experience with my 6 1/2 inch model 610. I've had days when I've managed a 2 inch group at 100 feet, however I've also had days when the best I can do is 4 to 5 inches. Since the only ammo I've used in the 610 is the Federal Champion 40 S&W, the only person I can point a finger at is myself. BTW, it's equipped with a J Point Red Dot and the SA trigger break is just a touch over 3 lbs. I'll also note that one day I experimented with resting the barrel on a sandbag and letting the 610 basically flip freely in recoil, that resulted in the gun shooting 6 inches high. My best results have happened when I rest the butt on a sandbag and fully control the recoil and as noted, some days I shoot it quite well and others I am pretty miserable.

Another factor that may be at play is that a 1 piece barrel does "whip" around when the bullet is transitting the barrel. This is magnified with the longer barrels because they are not as "stiff" as a shorter barrel. Ideally, with these barrels you want to produce a load that causes the muzzle to be at "center" when the bullet exits the barrel. The movement of the muzzle is a harmonic motion in some ways that resembles a pendulum. So, it's a matter of "timing" the load so that the bullet exits the barrel when it's at that ideal "center" point. Because of this, a long barreled handgun will prove to be more sensitive to load than a shorter barreled handgun or a handgun that uses some means to restrain the barrel at the muzzle and the frame.

BTW, this means a 2 piece barrel. I also have a model 620 and it's not only capable of astounding accuracy, it also seems to be VERY insensitive to loads. I've found that elevation will vary with bullet weight but the group size is quite stable.

There is a BIG difference between shooting at 50 feet and 50 yards. At you initial distance of just 5 feet over 15 yards just about anything should shoot well unless there is a barrel problem. If you're not used to 50 YARDS you may just need to practice. It's a stretch even with glass.

My 8 3/8" 629 Classic with my load is a 1/2" gun at 25 yards when I put it between my knees and used a braced sitting position. SAME gun and load at 50 yards(again, open sights) is a 4" shooter(and don't think I don't know whose fault that is!).

I'd work up a good 357 load, sight it dead on at 25 yards and then move back. At least in my case, 50 yards is shooter trouble.