S&W K-frame trigger/hammer problem


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orionengnr
August 7, 2014, 11:54 PM
Okay, I did a search and could not find anyone else with this problem.

Revolver is a Brinks trade-in M64-5 DAO (looks like it was made by S&W that way, but I'm not 100% on that). I bought it recently (used, obviously).

Sometimes, stroking the trigger does not cause the hammer to rise and fall. It moves just a very little bit, and that is all. Trigger moves through its full stroke, no jams or tough spots, although it does not feel as smooth as some. This only happens once in a while, so it's difficult to duplicate.

I took off the side plate, gently cleaned and lubed everything inside. Since then, I have only done some dry firing, and have not (yet) had the hammer fail to rise...but I'm not sure I fixed anything, because i did not find anything conclusive.

One thing I do note is that the trigger "stages" semi-normally, one click, two clicks, then the hammer falls. But the distance of trigger/hammer movement after the second click seems more than normal...and the effort after the second click seems to increase more than normal.

I don't have another DAO K-frame to compare to, so I'm comparing to my well-broken in, very smooth M-66 no-dash...may not be a valid comparison.

Any suggestions are welcomed.

Best regards, Rich

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BBBBill
August 8, 2014, 12:52 AM
Sounds like the double action fly (sear) may be sticking. That part is pinned into the front lower part of the hammer. It is spring loaded by a small spring a recess in the slot. The spring may be corroded/bent/kinked.

For reference, part numbers 49 and 50 in the link - http://www.gunpartscorp.com/Manufacturers/SmithWesson-33495/Revolvers-42026/KFrameRevolvers-38382/64-5-36817.htm?page=3

Should you find that it needs to be replaced, the fly (sear) is not a drop in part. It must be fitted for proper operation.

Jim K
August 8, 2014, 02:36 PM
A sticking double action sear is one possibility; another is that the trigger is not returning fully so it can engage the DA sear. Dirt or crud can cause that, also, along with some other things.

Jim

orionengnr
August 8, 2014, 07:54 PM
I took off the side plate (again) and removed the hammer.
I also happen to have another K-frame (albeit not DAO), and did the same with it. I compared the length and the engagement faces of both, as well as the amount of force required to compress the spring acting on the DA sear. I also checked the amount of pressure exerted by the rebound slide spring, and checked to make sure both triggers are going fully forward.

I cannot discern any difference between the two.

I cannot swap them out, because one has the hammer-mounted firing pin and the other has a frame-mounted firing pin.

There is definitely a difference in the force required to reach full travel (greater on the that has experienced trouble). After having both side plates off, both revolvers are clean and well lubed inside, and it appears that everything that should move is moving relatively smoothly.

I was thinking of buying a standard hammer from Numrich (one with a hammer spur, complete with DA sear). Will this require a gunsmith's fitting?

Thanks again for your help.

Best regards, Rich

rcmodel
August 8, 2014, 09:20 PM
Yes, it will very likely require fitting to the trigger.

Before you do anything else.

Try taking the strain screw out of the one gun and try putting in the other gun causing the problem.

If no noticeable difference?

Swap the mainsprings and try that.

rc

Jim K
August 9, 2014, 12:59 AM
You might also try swapping trigger return springs while you are at it.

Jim

orionengnr
August 9, 2014, 11:44 AM
Okay, I'm not sure how I managed to miss this...but, the DAO M64 is a round butt, while the other is a square butt.
--The two strain screws are different lengths--is this a function of the round/square butt?
--The mainsprings have different curves to them as well.
--The "short" (round butt, DAO frame) strain screw is barely long enough to touch the "other" mainspring, while the "long" strain screw will clearly over-bend the (round butt, DAO) mainspring.

So now, everything is back where it began. If anything, I'm thinking I should buy a new standard mainspring and a new strain screw, and go from there.

Your thoughts?

rcmodel
August 9, 2014, 12:53 PM
O.k.
All K, L, & N mainsprings are the same, but RB & SB strain screws are different length.

Here is what a SB Model 66 spring & strain screw should look like.

201424

Can't help on a RB strain screw length, but RB & SB springs are the exact same.

I think I would replace both the mainspring & rebound springs and see what that does.

http://www.gunsprings.com/index.cfm?page=items&cID=3&mID=58

Maybe someone else has a RB K-Frame and could measure the strain screw for you?

rc

JDBoardman
August 9, 2014, 09:04 PM
I just measured the strain screws on my S&W 66-2 and my wife's 65-5. Both are K-frame round butt, and the length for both was 0.675". Your strain screw may have been shortened to lessen the trigger pull, and now the spring is "knuckling", or catching up under the hammer because it doesn't have enough pre-bend.

John

4v50 Gary
August 9, 2014, 09:16 PM
That mainspring hammer screw is not a strain screw. It should be screwed in all the way.

rcmodel
August 9, 2014, 09:45 PM
May be?

But S&W calls it a Strain Screw in every parts list, & the S&W Armorers School Shop manual.

What should we call it? :confused:

rc

Jim K
August 9, 2014, 10:15 PM
A strain screw is intended to put tension on a spring. That does not mean it can or should be used as an adjustment screw. The main purpose is to allow easy installation/removal of the mainspring, not to allow trigger pull or hammer force adjustment.

Jim

orionengnr
August 9, 2014, 10:40 PM
4v50--

"Strain screw" is S&W's nomenclature, not mine.
I understand the function of the screw, and am only using correct terminology. Can we stay focused here, please?

Thank you.

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