Light Primer Hits with Quick Followup Shots

[HorizontalMike]

I started getting light primer hits on my 4in 1986 "bought new" 686 recently. Had a professional trigger job done Jan 1987 by LGS. Had zero problems over the years, so was surprised when I started getting light strikes.

After thinking on this for quite some time, I finally surmised that only recently, this past year, began shooting my 686s in multiple rapid DA. Shooting slowly, I experienced no misfires, however on a quick followup the misfires were occurring. I'm guessing that I am just now finding out the parameters of my +30yr ago trigger job. Better late than never...

Looking at my attached notes:

• Top Left is my "problem 686" and on Right my other 686 that shoots just fine, and I compared both on same day.
  
• Both had/have similar trigger pull weights, but 686 on left misfires.
  
• The left 686 showed light strikes when looking at unfired primers.
  
• Replaced Strain screw with unaltered NOS Strain screw and standard Wolf Spring Kit. Calculated the Wolf mainspring groove offset 1/2-length of the old "trigger job" shortened strain screw.
  
• Got similar trigger weights, but noticed my B/C gap had increased from 0.003in to 0.005in.
  
• I had inserted two 0.002in endshake washers when adjusting endshake, so decided to take one washer out. Got my 0.003in B/C gap back and still managed less than a thousandth endshake.

QUESTION:
Could having the endshake adjustment TOO TIGHT, actually be "causing" the misfires (light primer strikes)? .

 

[armorer951]

The answer to your endshake question, and perhaps your dependability issue, may be in the rear gauge or "headspace. Correct headspace, checked when the gun is clean and properly/completely assembled, should fall between .060" - .068". (The closer to .060" the better) Out of spec. rear gauge can cause misfires. "Too tight" a front gauge might impede cylinder rotation (by contact) and cause issues, but I doubt this is the source of your misfires.

Improper timing and cylinder alignment, a dirty cylinder assembly, short stroking, and a litany of other issues can also contribute.

 

[HorizontalMike]

Both are No-Dash 686s.
Both are "M" modified.
Just measured headspace and get 0.063in with free movement (higher have drag but can be forced a bit).
B/C gap is 0.003in

I will retry sometime this week. I limit my home range to exclude weekends, and to be PC with my neighbors.

 

[BLUEDOT37]

Could having the endshake adjustment TOO TIGHT, actually be "causing" the misfires (light primer strikes)?

From the look of your strain screw picture it's flared/flattened tip is likely the cause of the FTFs. I can't see how too little endshake would cause that. It just got tired & needed replacing.

.

 

[HorizontalMike]

Maybe

From the look of your strain screw picture it's flared/flattened tip is likely the cause of the FTFs. I can't see how too little endshake would cause that. It just got tired & needed replacing.
.

As far as "too much/tight" endshake, I noticed that using 0.004" shims, changed my B/C gap from 0.003" to 0.005", and that was when I started getting light primer strikes. Will need to get a range session in to see how my adjustments now work...

I agree,... that may indeed be the cause. I am thinking that the original "trigger job" I had back in 1987, may have been when THAT strain screw was flared/flattened. I went so many years ONLY firing my 686 in SA, that I honestly don't remember when I started shooting it in DA...

Anyway, just got another three (3) strain screws in, for a total of four. That said, I "may" try adjusting, aka shaving the end of the strain screw, a bit to reach the "best" trigger action. However, I do want to make sure that I have done/modified everything I can before I go that route. I have stoned the return spring housing, as well as the extractor rod channel, and anything else I could find. Have some specialty stones on the way, for all the nooks and crannies.

 

[ken158]

I think your “professional” trigger job included a filed flat mainspring screw...

 

[HorizontalMike]

QUESTION:
What are the possible causes of the differing readings between "quick" trigger pulls and "slow" trigger pulls?

• Is it only apparent with the electronic measuring devices like the Lyman?
• Will actual hanging weights do a much better/precise job of recording the true trigger pull weight?
• Is there any way to interpolate the disparity of readings on an electronic Lyman trigger pull?
• Does such a disparity hint at "other" issues dragging on the trigger action?

 

[Protocall_Design]

Trigger pull weights are somewhat meaningless as a way to compare one gun against another for misfires. There are too many variables involved.

The better way is to measure hammer pull weights. Cock the hammer, hook the trigger pull gage under the ledge on the front of the hammer, and gently lower the hammer till the gage contacts the frame. Pull the trigger and hold it back to keep it out of the equation. Now pull on the trigger gage and see what the reading is just as the gage lifts off the frame. Write down that reading. Raise the mainspring tension until there are no misfires and write down that reading. The last one is the one you want to keep for future reference. If you work on the gun or replace the mainspring later, you can reset the mainspring to the recorded value with a high level of confidence that it will work.

The same setting may or may not work for another gun, as each gun is an individual entity. Every gun (or anything else) is the sum of all the parts, each piece with their own plus or minus tolerances, and how they all interact with each other.

 

[armorer951]

Is it only apparent with the electronic measuring devices like the Lyman?
Any hand held device has an inherent flaw....and that is, whoever is operating the gauge itself. Too many variables to be consistent. This is not the fault of the person operating the gauge. Even high quality pull gauges are inherently inconsistent by design.

Will actual hanging weights do a much better/precise job of recording the true trigger pull weight?

Hanging weights eliminate some of the variables, but not all. The gun needs to be in an inflexible fixture, the weight must be suspended centrally below the trigger, and at the same place on the trigger itself, and, additional weight must be added in very small increments until the trigger actually cycles. If as many variables as possible are eliminated, then yes, hanging static weight is a better way of measuring in terms of consistency.

Is there any way to interpolate the disparity of readings on an electronic Lyman trigger pull?

I'm assuming you mean "interpret".....if so, no, I don't think so. The readings are too inconsistent in my experience. (Sorry, but I'm too stupid to know what "interpolate" actually means)

Does such a disparity hint at "other" issues dragging on the trigger action?

No, not necessarily. Once you have a way of measuring the trigger pull consistently and accurately, then interpretations concerning changes (to the internals of the gun) are much easier. Without a repeatable protocol, interpretation concerning what is actually causing changes in readings is just about impossible.

 

[HorizontalMike]

Trigger pull weights are somewhat meaningless as a way to compare one gun against another for misfires. There are too many variables involved.

The better way is to measure hammer pull weights. Cock the hammer, hook the trigger pull gage under the ledge on the front of the hammer, and gently lower the hammer till the gage contacts the frame. Now pull on the trigger gage and see what the reading is just as the gage lifts off the frame. Write down that reading. Raise the mainspring tension until there are no misfires and write down that reading. The last one is the one you want to keep for future reference. If you work on the gun or replace the mainspring later, you can reset the mainspring to the recorded value with a high level of confidence that it will work.

The same setting may or may not work for another gun, as each gun is an individual entity. Every gun (or anything else) is the sum of all the parts, each piece with their own plus or minus tolerances, and how they all interact with each other.

Interesting method! I'll give it a try, though I'll need to figure out how best to hang vertically. Currently using a tail vise on a woodworking bench (with soft jaws).
Thanks!

 

[HorizontalMike]

Is there any way to interpolate the disparity of readings on an electronic Lyman trigger pull?

I'm assuming you mean "interpret".....if so, no, I don't think so. The readings are too inconsistent in my experience. (Sorry, but I'm too stupid to know what "interpolate" actually means)

Interpolate is just trying to... estimate values of (data or a function) between two known values. In other words, would it be possible to fine tune my trigger pull readings. Very close to what your response was. Thanks. I was not trying to overstate or mislead anyone. Sorry about that.

Yeah, you can tell by the varied readings I got, and "each" was an average of 10-pulls. I kept practicing with the Lyman, however it really is hard to remain consistent...

 

[Protocall_Design]

Interesting method! I'll give it a try, though I'll need to figure out how best to hang vertically. Currently using a tail vise on a woodworking bench (with soft jaws).
Thanks!

With the trigger pull gage, you don't have to hang vertically as you do with weights. Sideways works fine. You can put the barrel in a padded vise, parallel to the floor. What you're measuring here is how much mainspring tension it takes on the hammer to reliably fire a particular brand of primer.