Smith model 66 - Light Strikes (what parts do I need)


March 18, 2010, 11:59 AM
I picked up a used Smith model 66 (66-4 I believe)

Supposedly owned by long term customer/Smith Engineer, I picked it up on consignment for a good deal.

Fantastic double and single action trigger... which light strikes on winchester white box and defense loads (Hornady). Almost once per cylinder.

So I need more reliability than this ridiculously smooth and light trigger.

I've done 1911 enhancements before (Kuhnhausen books, etc), but this would be my first foray into revolvers.

What do I need from (Brownells instead?)

Thank you,

[I assume it's a main spring or trigger spring of some sort would be easiest]

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March 18, 2010, 12:31 PM
First thing to do is make sure the main spring strain screw in the front of the grip is tight.

It may also be tight, but grond off to provide less mainspring tension.

I would replace that if it shows any indication of being ground off.

A new strain screw #53, mainspring #34, & rebound spring #46 should return it to normal 1000% reliability.


March 18, 2010, 12:41 PM
Should your 66 turn out to have a square butt I believe you'll find replacement strain screws to be out-of-stock everywhere - including Numrich last I checked.

Member Stainz provides a work-around:

Old Fuff
March 18, 2010, 12:46 PM
There are a number of things that could cause or contribute to the problem, and without having the revolver on a workbench it's hard to say what... :confused:

But if the double-action trigger pull is, "ridiculously smooth and light," I would suspect that the original hammer (and possibly rebound slide spring that controls the trigger) have been replaced or modified. If this is the case I doubt that the previous owner was any kind of S&W engineer. The solution is to replace those springs.

Another possibility is that the mainspring strain screw (located at the lower/bottom of the frontstrap) is either partly unscrewed or has been shortened. If so, replace the screw.

The practice of messing with spring tensions and shortning the strain screw are commonly used by individuals that lack any real knowledge of what they are doing, and the trigger pulls that they come up with are often excellent, but unable to reliably pop a cap under any and all circumstances.

Since you apparently have no background when it comes to working on revolvers I would suggest two options: Order a copy of Kuhnhausen's S&W revolver shop manual and a set of S&W specific screwdrivers from Brownells to start with. You may want/need additional things later, but read the manual first.

Another choice would be to return it to Smith & Wesson and have them go over it. But if the lockwork has been "polished" by some dingbat and there is more involved then just a screw or springs the work might get expensive.

This isn't the sort of thing they fix (or should have to fix) under warrantee.

Old Fuff
March 18, 2010, 01:29 PM

Trust the Old Fuff, ask no questions, and use the following link: :uhoh:

Look at page 7, item #55

Oh, and don't tell anybody, this is just between you and me... :evil: :D

March 18, 2010, 03:33 PM
Old Fuff! Thank you for the knowledgeable post. I always appreciate your input. [Everyone else, thank you too!]

I will post pictures of what I find and get more knowledgeable info. Stay tuned!

I didn't know the big K made a S&W book... Christmas anyone (if I can wait!!)?

March 18, 2010, 04:52 PM
In addition to the above referenced screw, also check to make sure the mainspring hasn't been modified. I've sent Smiths to Clark Custom Guns for their trigger job, and they always modified (bent) the mainspring to relieve some of the tension.

David E
March 18, 2010, 05:05 PM
All good suggestions and all probable causes.

Two things: It's remotely possible the firing pin is too short. Something to keep in mind, but I'd save it for last.

Secondly, if the strain screw has been ground down and no replacements are available, what I did once is take a large pistol or rifle primer, deactivate it with WD-40, then pry out the anvil and priming compound, leaving only the primer cup. Put that on the end of the strain screw where it contacts the mainspring. This effectively increases its length. It won't fall off. Depending how much the screw was shortened, this might make enough difference in the main spring tension. Give it a try while you wait for your backordered strain screw to come in.

March 18, 2010, 05:31 PM
I think S&W hadn't started using the short firing pins back when they still made the 66.

March 18, 2010, 05:59 PM
Sometimes owners will shave the sides of the mainspring. All the above are possible, except the rebound spring. That won't need replacing unless the trigger isn't returning to battery. Also, check for endshake and the space between the case head and the revolver frame (headspace). If it's greater than .009", it's excessive. (I've seen them as much as .013).

March 18, 2010, 06:57 PM

Trust the Old Fuff, ask no questions, and use the following link:

Both I and my formerly troubled 686 (also part 55) thank you. It's good to know it's back among the living.

But I grew impatient and invoked the Stainz JuJu with passable results from back when I was grousing about the absence of said screw.

As I recall I actually irritated one of your followers by implying that the difficulty of obtaining square butt strain screws took some of the luster off the older models so inflicted. Tis a pity that minor amusement will now be denied me.

But it's much better to actually have the part available.

Old Fuff
March 18, 2010, 07:11 PM
I didn't realize you had lowered yourself to buying stainless... :neener: :D

Maybe I should go back and look for a stainless one too. :uhoh:

Anyway I suggest you lay in a small supply while they are available, just in case, for sometime during the future. They may be new, but I suspect they came from revolvers that were reduced to parts, and then the frames returned to some police department so that they could be destroyed to keep they're anti-gun masters happy. :barf:

Be aware the pre-war and World War Two era screws have different threads.

I have regressed to looking at revolvers made during the late 19th century and early 20th. They are the last stronhold of best quality... :cuss:

March 18, 2010, 08:24 PM
I didn't realize you had lowered yourself to buying stainless...

But of course you did: 629s, the Anaconda, the early 686s without the "M" stamped on the crane, the 66s, etc. All these things you've advised and helped me with.

You forget how much you've contributed.

I didn't jump on the "Old Fuff should write a book" thread as I've usually been able to resurrect what I needed with the "search" function, but one thing has eluded me:

Can you steer me to the post where you discussed a Navy trial of interchangeable parts vis a vis S&W vs. Colt?

...or am I just imagining the episode?

...good idea on stocking up while available. It may just be me but it seems most "light striking" pre-owned S&Ws were the result of using the "adjustment screw" rather than actually working on the parts or finagling the spring - given the ease of jacking with the strain screw it seems few felt compelled to take it further. At least in my limited personal "molested" S&W experience anyway...

March 19, 2010, 09:20 AM
So I need more reliability than this ridiculously smooth and light trigger.

I would start by finding a unmodified strain screw and main spring.

March 20, 2010, 03:07 PM
FWIW: Here is a box-stock mainspring & strain screw out of my Model 66.
Measures .580" OAL.

Spring is basically straight in the middle with a slight bend on each end.


March 20, 2010, 03:17 PM
Try some Federal ammo. It has the softest primer cups. It is more likely to be 100% reliable with a reduced trigger pull.

If you're asking about this, I don't think it is a good idea for you to be taking the gun apart to that level. Changing the trigger return spring is a PITA if you do not have a special tool/experience. You need to match the trigger return spring to the mainspring, else the trigger won't reset. Taking the sideplate off will damage it if you do it wrong. You just can't pry on things with a screwdriver.

Steve C
March 20, 2010, 04:45 PM
If tightening up the mainspring strain screw didn't work you can go to Wolf Gun springs at this link and get an improved mainspring in standard strength or a calibration pack of 3 springs with variable tension.

I replaced the OEM mainspring with one of the Wolf standard powerrib mainsprings on my 66 and it improved the trigger pull somewhat and has been 100% reliable with all types of ammo and primers for 20+ years.

March 20, 2010, 09:20 PM
Spring looks like it has a nice curvature to it.

However, I had a number of turns I could do to increase the tension, and now the trigger pull, although heavier, feels 'good', and I bet I have no more light strikes!

I will range test it again, but I bet this little bit did the trick. and I didn't have to disassemble the gun. Just took the grips off, and adjusted that one screw!

Thanks gents.

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