Reducing DA and SA trigger pull on current S&W revolvers.

[andyo5]

My usual approach to reducing trigger pull has been to replace the stock rebound spring with a 14 lb Wolff version, and then to shorten the strain screw until I get close to an 8 lb DA trigger. I then may rejigger the rebound spring to achieve a 3 lb SA pull. These guns all shoot well, with Federal primers.
But my new 686-6 and new 629 Classic do not respond to this approach at all. Oddly, shortening the strain screw has no measurable effect (trigger pull gauge) unless you remove so much length that the single action sear doesn't always hold. Not acceptable for obvious reasons.
An alternative method is to use the Wolff Type I mainspring with a full length strain screw and a 14 or 15 lb rebound spring. It feels great in both SA and DA, but it will only set off Federal primers (tried it only on the 629) and won't fire Winchester primers even in single action.

Currently, I have both with factory mainspring, full length strain screw, and 14 or 15 lb. rebound spring. The reduced power rebound spring does help.
DA is off my scale (probably about 12/13 pounds) and SA is 3 pounds (good).

Since these guns are to be used for competition or carry, I'd like to stay around 9 lbs in DA and 3 lbs in SA.

I can't imagine what is different about these guns as compared to my 2005 era M625s or my M686-4. There must be some design differences, I just can't figure out what they are.

Any suggestions?

 

[series guy]

My first suggestion is to never modify a carry gun. If you ever need to use it you won't notice an extra pound or two of trigger pull and the modifications can surely be used against you in court if it comes to that. I'm pretty sure Mas has cautioned against this many times in his writings. On my target only guns I lightly stone all moving surfaces and lap the rebound slide in the frame. I never touch the sear surfaces. Then I install a lighter rebound spring, a power rib main spring, and an allen head set screw w/locking compound from Mcmaster Carr. Most of the time the result is a 2 1/2 pound S/A trigger and an 8 pound D/A pull. The original parts go in a small zip lock bag with a card bearing the guns model and serial number in case I want to sell the gun at some time.

 

[andyo5]

and an allen head set screw w/locking compound from Mcmaster Carr. Most of the time the result is a 2 1/2 pound S/A trigger and an 8 pound D/A pull. The original parts go in a small zip lock bag with a card bearing the guns model and serial number in case I want to sell the gun at some time.

Same thing that I did at first, except for the set screw.
What is the spec. for the set screw? Is it an 8/32? And what length do you use?
Do you find that the resulting gun will only ignite Federal primers?
Thanks.

 

[series guy]

The set screw is McMaster # 95235A507 10/$4.86. I have never used Federal primers, usually Winchester. I often use a 12 or 13lb. rebound spring. Every gun is different when it comes to tuning. Once in a while I end up with a 9# D/A trigger to get reliable ignition but when they are really smooth the weight always feels lighter than it measures.

 

[andyo5]

How do you determine how far to screw in the set screw? With the strain screw, the screw head determines that for you. Do you screw it in until you get a particular DA pull force?
Also, the Wolff Type I mainspring has a groove in the center. The tip of the strain screw falls into this groove, reducing the amount of strain obtained. I find that I have to use a steel shim between screw and mainspring to counteract this. What do you do?

 

[series guy]

I turn the strain screw in until I like the bow of the mainspring. The dip in the center of the power rib spring is why I use a 1/2" long set screw. Then I use a Wheeler trigger pull gauge to test. I always start at 8lb. D/A and then test fire and adjust as necessary.

 

[andyo5]

I noticed that I have several 'virgin' strain screws for K/L round butt. Total length is 0.500", which is 0.033" longer than the one that came with the gun. I am thinking that I might try one of those with the Wolff mainspring to see it it will get me where I want to go. The extra length might be enough to make up for the 'dip' that you mentioned.

 

[series guy]

I have a feeling they won't be long enough. The .500 set screws are always recessed in the frame.

 

[andyo5]

I have a feeling they won't be long enough. The .500 set screws are always recessed in the frame.

I just tried it. I'm getting 8lb/3lb with my spring loaded RCBS trigger gauge.
I plan to test it tomorrow with Winchester primers. If it will light them off in DA mode without fail, it is good. The feel of the trigger is great. I may go ahead and order the set screws anyhow, to provide additional adjustment.
I'll let you know. And thanks for the ideas.
I also ordered a Lyman electronic trigger gauge earlier today.

 

[Rule3]

The "strain" screw or mainspring screw is not an adjustable item. It is not intended to be a trigger pull adjustment.

 

[dr. mordo]

You might want to pick up the Miculek Trigger Job video from his site. He walks step by step thru the process and has offers one or two tips I have never seen anywhere else.

 

[lefty_jake]

The thread below discusses how to measure the mainspring tension by testing the hammer strength with a trigger scale. Post #2 has an illustration of how to do it.

question about testing hammer spring weight

While measuring the double action pull weight does give an approximation of mainspring tension, other factors, such as friction and the rebound spring weight, are also included in the double action weight. Weighing the tension on the hammer removes those factors.

I have found this method to be very helpful when I am working with mainsprings.

 

[retired2006]

With the revolvers that have the frame mounted firing pin, I like to use a Cylinder and Slide extra length firing pin. Brownells has them. If you are ordering the firing pin, also get a new return spring for it.
This works for me.

 

[armorer951]

When using this method for evaluating mainspring tension, be sure to follow the illustrations carefully and consistantly, particularly when considering the placement (position) of the weight arm on the face of the hammer. The minimum weights in the full illustration in the link are factory recommendations for service revolvers.

question about testing hammer spring weight

 

[andyo5]

I have a feeling they won't be long enough. The .500 set screws are always recessed in the frame.

Series guy, I tested the DA trigger this morning with Winchester 38spl white box ammo, and it worked every time. Eight rounds fired. I think it is good now. I might substitute a 15 lb rebound spring for the current 14 lb version, to slow down the overtravel after ignition.

 

[series guy]

Sounds like you're good to go. On the subject of the strain screw not being an adjustment screw I agree completely.....for a factory stock revolver. Once you start changing springs using a set screw to dial in function and trigger pull is way better than modifying the strain screw. All the original parts from my guns go in a small zip lock bag properly labeled so they can be returned to stock at any time.

 

[H Richard]

You can only get so far with a trigger swapping springs and strain screws. Careful stoning of certain parts and lubrication will finish up the job. I have known smiths to take a stock mainspring and carefully reduce the width and thickness of the spring as well as the shortening of the strain screw. This work is done on competition revolvers, not any carry pieces.

 

[Protocall_Design]

If you want to use a regular strain screw, you can use the setscrew to make adjustments until you find the best hammer weight setting. Record that number, then incrementally shorten a strain screw to duplicate that hammer weight.

 

[andyo5]

If you want to use a regular strain screw, you can use the setscrew to make adjustments until you find the best hammer weight setting. Record that number, then incrementally shorten a strain screw to duplicate that hammer weight.

My usual practice has been to back out the strain screw in 1/4 turn increments until I get the action that I want. Knowing the pitch, I can then calculate how much to shorten the strain screw to get the same effect.
An 8-32 screw has 32 threads per inch. So each turn equals 0.03125 inches. One quarter turn equals 0.0078 inches (round up to 0.008") and so on.

 

[Engineer1911]

My usual practice has been to back out the strain screw in 1/4 turn increments until I get the action that I want. Knowing the pitch, I can then calculate how much to shorten the strain screw to get the same effect.
An 8-32 screw has 32 threads per inch. So each turn equals 0.0312" inches. One quarter turn equals 0.0078 inches (round up to 0.008") and so on.

You dropped the first 0, you want 1/32 not 5/16. I fixed the error.