I took my S & W 686 out to the range today. Shot great. When I came home to clean it I saw a small mound on the outside top of each cylinder. Each mound was the same size and the same place. I was shooting AE .38 lead. I don't see how lead could end up on the outside of the cylinder. And I'm not sure it was lead but I don't know what else it could be. At first I thought it was a gouge but it came of when I used some Flitz and a brush. Any ideas? Only other thing I've done is put Rennisance wax on it.

Carbon, maybe?

Having a little show up on the side of cylinder at the forward edge is not unusual, it's just some blow by that's getting channeled back by the topstrap.

I've shot some handloads that seemed to "vaporize" some of the lead, causing it to build up on the cylinder face and rear of the barrel. But, could of been more carbon than lead. Brass brush and Hoppes No. 9 does pretty well. Slower powders, too.

Could be that the cylinder and barrel throat are not in line and a bit of lead is being peeled off the bullet as it crosses the cylinder gap..  Might be a cylinder timing problem too.  I'd take it to a gunsmith or send it in for factory eval.  If you shoot it again and the same thing happen, please post pics.  I'd advice a good check up by a knowledgable professional first.  Just to be safe.

From my simple testing the chambers and bore are in line. I've never used this ammo before. I've also never fired this weapon before. Come to think of it, I didn't clean the damn thing before I shot it. I bought it used but it looks barely used. I'm going to clean it up good and fire some differnt ammo through it. The AE did have a lot of smoke to it so it's probably pretty dirty.

Pics would help. Lead on the face of the cylinder wouldn't be unusual. Carbon deposits can build up in odd places sometimes.

This is normal, especially when shooting lead bullets.

There is a gap between the barrel and the cylinder that allows some escape of the blast.  The blast carries with it some carbon and lead, and this flows out of the gap and back over the cylinder.  This deposits carbon and lead on the top or outer edges of the cylinder, right over each chamber.

Totally normal, there's nothing wrong with the gun, unless the barrel/cylinder gap is excessive and is allowing too much gas escape.

Ideally, you'd have from 0.004" to 0.007" barrel/cylinder gap, with 0.005" being "about" perfect.
Currently, S&W is passing gaps of as much as 0.012" as being in spec.
To check, push the cylinder to the rear and hold it there while you insert automotive feeler gages into the gap until you gage the actual gap.

While you're doing the above, you might as well check endshake too. Push the cylinder all the way forward and insert a feeler gauge. The difference between the two measurements is the amount of endshake.

Thanks. I'll find my guages and check it.

Your pistol is seriously flawed and potentially dangerous It should be sent to me for disposal. I'll waive my fee if you can send some ammunition or small pistol primers  

I figured it out. The lead bullets were vaporizing and hitting the front screw hole on the rear sight on the underside of the top strap and falling on the cylinder.

Any revolver shooter that shoots many lead bullets should own a 'Lewis Lead Remover'. Handy for any firearm that shoots lead bullets.

A simple little kit with caliber adapters that uses brass screen patches to scrub lead from bores, cylinders, and forcing cones.

I lost my Lewis kit for a couple years after my last move, and bought some 'Outers' single caliber only lead remover gear, similiar to genuine Lewis deleading gear, it's decent for the cost. The Lewis Lead Removers are better, but fairly pricey.

Most larger gunstores should carry one or the other de-leaders.

They also make lead removing cleaning patches. The ones I've used look like thick cleaning patches, but are treated with some sort of cleaning chemical or other substance These do seem to work on to a degree on really smooth chambers and bores with light lead problems, but not so good on lots of lead or guns where the bore is not just polished shiney.

Crappy lead bullets cause most leading problems. Ammo loaded with bullets too soft, or too soft a bullet at too high a velocity without a gas-check will lead the shit out of things. Good or bad bullets not lubricated properly are a prime culprit too. Bullet lube is extremely important to avoid leading. Shitty, shoddily made guns with out of spec bores and cylinders may lead no matter what.

Also bullets too large for the bore, or too small for the bore can cause some nasty lead problems. Bullets of the proper hardness, at the proper velocity, properly lubed, in a good gun take quite a few rounds before any lead issues may pop up.

I'll check into it.