I shot my 686 at the range last night and it's accuracy was pretty bad...AT 15 YARDS!  I fired 40 rounds of PMC 158gr. .357 and they went all over the place.  This has never happened before.  I thought Maybe it was me since I haven't fired it in about four months.  I loaded up the HK USP .45 and made a silver dollar hole in the head of the target with twenty rounds.  

This is where it gets interesting...now confident of my marksmanship, I place ONE round in the cylinder of the 686 and it went straight through the 10 ring of the target.  I then fully loaded the cylinder, and the accuracey was back to garbage.  The cylinder has a little play in it, but nothing worse than any other S&W I've ever handled.  The bore is like a mirror with absolutely no leading.  Any ideas why this revolver can't shoot worth a damn when its cylinder is fully loaded.  BTW, this has never been an issue in previous trips to the range.

Have you tried different ammo yet? I've never gotten real good accuracy with 158gr ammo. I stick with the 125gr & have real good results there. Also have a different shooter try the gun.

This seems to be a new problem.  I doubt it is the ammo.  158 grain is the prefered bullet size more 357 mag shooting.  My guess is there is a problem with the yoke.  Maybe a hairline crack or something.  I wouldn't screw with it.  If you are sure it is not you then send it out for a tuneup.

Sounds like an ammo problem. Soft lead bullets and magnum velocity perform poorly. You state that there wasnt any lead in the bore. So I assume you were shooting lead.......

Try this to see if your revolver is out of time....mark each cylinder 1-6 with a pencil.

Fire a 6 shot group using #1 cylinder.......and so on through the remaining 5. Shoot off of a rest with bags to eliminate most of the human error.

Try some quality (fedral, remington) jacketed ammo.

BTW 125gr Rem GS 357's shoot into 1/2" @ 25yds out of my 686. I dont see how yours could shoot like crap all of a sudden unless it was ammo related or the gun was droped on its cylinder.

Good luck

Oh man. I just bought a 686P (7-rd cylinder), to be delivered soon. I hope this isn't a harbringer of things to come. [:\]

Quoted: Oh man. I just bought a 686P (7-rd cylinder), to be delivered soon. I hope this isn't a harbringer of things to come. [:\]

slt223's problem is the exception to the rule with the 686.

I used to have a 686 that was a really good shooter. It was second only to my old Colt Gold Cup National Match.