Had a trigger job done on the 686 a couple of years ago.  It has recently started light striking, when I talked with the gunsmith in the fall he said it probably needed a new spring.




For the un-educated what spring is he talking about?  Is it the one under the grips and what should I go with as it was running good before but I don't want the stock pull weight.

If it was good and now it isn't, first things I would check is to make sure all the inner works are clean and tight and there is no front/back play in the cylinder. Yeah, I assume by "spring" he means the main spring under the grip. If the stock spring was replaced with a reduced power spring, and you haven't shot it to the point you know you wore it out, you may just have to settle for stock spring tension. If the stock spring was bent to reduce the power to lighten trigger pull, you could try bending it back, but they're only a few dollars and you can figure out how to replace it just by looking at it. Good luck.

The big leaf spring in the grip was changed or modified to make a lighter DA pull, probably along with the trigger rebound spring.  Didn't do it right.

Get the junked springs out.

Replace them with factory full power kits from Wolf via Brownells.

You just learned slightly stiff is way more fun than click.

The fanciest Wolf spring makes the hammer go KWangggg.  Steda thunk.

Number one reason for misfires in a smith is a loose strain screw. The screw at the bottom front of the grip frame.(you may need to take grips off to see it) make sure it is fully tight. If it is even 1/2 a turn loose with a lightened mainspring it can misfire. If it is fully tight and still misfiring put a new full power mainspring in

THIS.

Take off the grips and give the strain screw a half turn in ( clock wise ) , that should do the trick.

Depending on the style of grips, you may not have to remove the grips.   Note the photo I posted of my Model 10.  The red dot indicates the location of the screw.   Some grips cover this.   Remove those.

Strain screw loose? Loctite is your friend.

Did you change ammo?

Some primers are harder to ignite.  Some action jobs marry you to Federal Primers..  Softest on market.

strain screw is not loose, looks like a new spring is in order?

what should I order?

Go to a local hardware store and get some allen or torx head set screws in the same thread as your factory screw (I think I did either 3/8" long or 1/2" long, 8-32 thread, maybe 3/8" for K/L frame and 1/2" for N Frames??).  When I switched to a lighter main spring to reduce the trigger pull, the factory strain screw wasn't long enough to get the correct arc on the new main spring and be reliable.  The trigger felt strange at the end of the pull, like the hammer was releasing early or something?  With the longer set screw, you can tighten it more and get the correct bend to the main spring for more reliable ignition and then lock tite it in place.  This will let you run lighter springs, but still have enough to pop the primers.  It worked great on my 617 .22lr revolver.  It made the revolver trigger pull much lighter, without the strange pull feeling the lighter springs alone gave.  You can also lighten up the rebound spring of the trigger, too, but if you are shooting DA quickly, your finger may outrun the spring and the trigger won't reset all the way forward.

On newer Smiths, dry firing a lot and letting the parts polish themselves in works wonders, too.

Quoted for truth! The lose strain screw was the cause of my light strikes in my 625 Smith. My grips cover the screw of course. I watched a couple of Jerry Miculek Youtube videos on how to open up a revolver's side plate and the inner workings of a revolver. Now I feel almost as comfortable tweaking a revolver's trigger as I do a semi-auto or an AR... I put a witness mark on the strain screw to the grip frame with a White Out pen and Purple Loctite'd the screw... I've since had zero light strikes even with Wolff steel cased ammo; of which shoots more accurately than most American brass cased bulk ammo... to my pleasant surprise. I'm betting a half to a full turn of your Strain Screw will remedy your problem OP.

What is the difference between the leaf spring and the coil springs?

I mean what is the purpose for each?

I was just about to post for the same problem with my Ruger redhawk .44 mag. I will have to pull the grips tomorrow. I think the guy I got it from may off done a Home trigger job

Leaf springs were used for a few hundred years. And require a tentioning screw to get just right.

A modern coil hammer spring is essentially drop in.

Ok then let me ask this again.

There is a big arched spring and then typically 1-2 smaller coil springs.  Since I'm experiencing light strikes do I have to replace all springs or a single spring?

The big arched mainspring is the only one you need to concern yourself with.