New 986 Weak Primer Strikes

[Dundgren]

Hi,

Some time ago my dad bought a new 986. Right at the start it has had problems with light primer strikes.

Sending it back was never an option for him. He wanted to try and fix it as he really liked the revolver. Sending it to get fixed in the US is an absolute nightmare (we live in Sweden).

First we tried a S&W gunsmith here. He said he couldn't find any issues.

The mainspring screw is screwed all the way and remains there.

We have tried a longer firing pin.

The moonclips are the correct tk customs.

Light strikes with all brands of ammo. (besides a revolver that won't go "bang" with all brands is not a functioning revolver.)

I have even tried putting in a cylinder shim for excess endshake depsite it being new and me not believing it to be the issue.

I have cleaned where the firing pin is.

I shot it today and got 2 light strikes out 49 shots. Best by far compared to before but not acceptable at all. I also noticed a indentation below the firing pin where the hammer strikes. An issue or just a tool mark? Picture provided.

I would really appreciate any help. I'm at a loss. I just want to get the damn thing to work properly for my dad. Thanks.

 

[Jeppo]

Is there a chance the Swedish S&W distributor can handle the return for you?

 

[Dundgren]

Is there a chance the Swedish S&W distributor can handle the return for you?

I think too much time has passed for that now. Like a few years. Even if it was recent they would solve it by sending it to the states and we wouldn't see it for at least a year. I myself would just return the gun at the start and find something else. But what is done is done.

 

[armorer951]

Since the failures are so intermittent, a couple of random mechanical things to check. The rear gauge, or headspace between the rear of the cylinder and the breechface. This should be .064" - 068"....smaller is better. Use a feller gauge after cleaning and wipe down of the gun. Excessive end shake will cause the cylinder to move forward, expanding the headspace and causing ignition failures.

Dirt and shooting debris in the cylinder assembly. The assembly should be as clean as possible......to the point of completely disassembling at times, (or soaking) to clean everything, epecially the yoke and extractor areas. Use a good cleaner and a toothbrush.

Also, take a close look at the moon clips to make sure they are flat on both sides with no burrs. (lay them on a flat surface) Stone off any burrs.

Double check the mainspring strain screw. It may be in all the way and tight, but may have been altered. (shortened)

 

[BubbaBlades]

986 Light Strikes

Dundgren,
I had the same problem with my new 986. I also had the firing pin replaced with a longer one. This helped a little but I still got some light strikes.

I was going to send the gun back to S&W but I decided to try using a heavier weight mainspring. I replaced the mainspring with a factory S&W spring that I had left over from my Wolf Spring conversion on another L frame.

This fixed my light strike problem. The double action pull weight went up about 3/4 of a pound.
I hope that this information is helpful.

 

[Protocall_Design]

Also, check to make sure that the hammer is not contacting the rebound slide when the hammer is all the way forward and the trigger pulled.
Holding the hammer all the way forward, the trigger should have a bit of front to back movement (clearance) at the back of the trigger pull. The rebound slide will soak up a lot of hammer strike if the hammer hits it just before going fully forward.

If the gun has a "power rib" mainspring, I would change to a S&W spring, as mentioned above.

 

[H Richard]

Have you tried more than one brand of ammo? 9mm mfg. is not consistent in regard to the rim thickness and beveled relief in front of the rim. Some ammo may not work well with the TK clips and some may not work well with the factory clips. I have a 986 using factory clips and a dozen or so bought from Midway and Dillon and seldom have any problems, but occasionally get one with rims too thick and the cylinder binds.

 

[armorer951]

To go along with what Protocall said in message #6, also make sure your overtravel stop, or trigger stop if there is one, is not preventing the hammer from "finishing" properly. That is, preventing the hammer from coming fully forward each time the gun is cycled/fired. I'm not familiar with that particular model, but there may be a stop rod inside the rebound spring that functions as a trigger stop. You can safely remove that stop if needed.

To illustrate the hammer seat/rebound seat relationship that he mentioned, I've attached a photograph showing these two seats, and the clearance that is needed between them. Quite often, if too little clearance has been provided, the rear of the rebound seat on the bottom of the hammer will contact the front of the hammer seat on the rebound slide. This will absorb some of the force of the hammer itself, and can cause a malfunction/failure to fire issue. This malfunction most often ocurrs when shooters attempt to "stage" the hammer and trigger prior to firing in DA, and as a result the trigger doesn't come back far enough to move the rebound slide out of the way.
Incidently, this interface between the hammer and rebound seats, constitutes the primary internal safety in the modern S&W revolver.

You might also temporarily remove the hammer block from the gun and test fire in DA without it to determine if there is a problem with the block itself. I have seen hammer blocks that are too long, or bent, and as a result, they interfere with the hammer descent into the frame cavity. Removing it for testing will rule it out as a possible contributor to the problem. Be sure to re-install the hammer block after the test.

Also, as a reminder, during your examination and diagnosis of the problem, do not operate or cycle the internal action under full mainspring pressure. This can damage the internals/frame.

Note the rebound slide and hammer position at firing (hammer fully forward) .....and the gauge or space between the two parts. S&W calls this space "wink". (note that the hammer block and mainspring in this L-frame 686 have been removed for illustration purposes)

 

[lefty_jake]

I wrote an article on my blog about working on S&W triggers. There is a section on light strikes which is too long to include in this post.

The section of the article on light strikes is here:

Understanding spring strength and light strikes

You may also notice that the interference between the hammer and rebound slide, which is described in this thread, is not mentioned in the article. That is one of the great things about this site, is that for all things S&W, there is always more info available here. And thanks to @armorer951 for the great picture in post #8.