It's a strain screw--not an adjustment screw!

[S&WIowegan]

I just shot a match today in 6 degrees above zero F. One of the guys on my squad had ignition problems. His quote was: "I've got the strain screw turned out one turn but I don't know why my gun won't go bang?!?!" I looked at him for a minute and just suggested he try turning it in a half turn

My Carmoney special went bang every time for two 30-round stages. I attribute that to my superb ammo-making skill!

Bob.

A16841

[Carmoney]

My Carmoney special went bang every time for two 30-round stages. I attribute that to my superb ammo-making skill!

I agree with your assessment, Bob. You know how to make sure your Federal primers are well-seated (i.e. crush seated to below flush and starting to flatten). Superb ammo allows the revolversmith's work to shine 100% of the time!

[20nickels]

Most of the dirty work was done today. Only takes about 15 min. with a drill press and the proper taps (you should of seen the look on the shop owners face , he has a purdy collection of bone stock Rugers). I went all the way through so that I could put a set screw on each side of the strain screw then start the tap straight with the drill press turning only with yer hand. Once it's started Use an 1/8" bit with an 8/32 tap. The local hardware store only had allen screws that were double the length of what I had needed so I will grind them down tommrow and give this a try. The real acid test will be the range with Major PF loads, but I will post a follow up with more pics soon.

[stipo]

I didn't read ALL the posts on this subject, so if someone else has already covered this, my apologies.

I have thinned AND bent......but I also back the screw off when I want to. I just use some medium locktite on it after I get it set where I want it and have no problems thereafter. With medium strength threadlocker you can move the screw easily enough without heat if you want to.

My .02

[357454]

I use a simple strain screw stop that is built from a piece of brass tubing just small enough on the O.D. to fit inside the strain screw counter bore and large enough on the I.D. for the strain screw to go through it. I use a tubing cutter to cut the pieces as thin as possible then put the spacer on a fine flat file and moving it back and forth with a finger smooth the ends down. I then install the spacer into the gun and test fire it (for home testing I use special brass with the primer hole enlarged and seat a new primer) I fire the gun until I get a misfire and will thin the spacer until the misfires stop. After the spacer is fit it will normally stay in the frame when the strain screw is removed but can easily be removed with a small screw driver or punch. If you ever have a misfire you can simply remove the spacer rub it on a file (@ 10 to 20 strokes) and reinstall. If the spacer gets too thin I put a piece of thin leather between it and my finger while I am filing it otherwise you will begin to file your finger as well. As Carmoney mentioned I too install the screw as tight as possible, however I have never found the need for locktite.

[CJDOUBLETAP]

I didn't read ALL the posts on this subject, so if someone else has already covered this, my apologies.

I have thinned AND bent......but I also back the screw off when I want to. I just use some medium locktite on it after I get it set where I want it and have no problems thereafter. With medium strength threadlocker you can move the screw easily enough without heat if you want to.

My .02

+1

[Carmoney]

Don't worry, I keep a screwdriver in my shooting bag to help you guys out when your revolvers start misfiring during the match.....and with any luck you'll only blow one stage.

[revoman]

Over 30 years with loctite and not one misfire due to the strain screw backing out. I wish I could say that about me.

[CJDOUBLETAP]

Don't worry, I keep a screwdriver in my shooting bag to help you guys out when your revolvers start misfiring during the match.....and with any luck you'll only blow one stage.

How did I know you would say somthing like that.

[wagonpilot]

Don't worry, I keep a screwdriver in my shooting bag to help you guys out when your revolvers start misfiring during the match.....and with any luck you'll only blow one stage.

I did my second ever revolver IDPA match Sunday with my totally stock, unaltered 686 SSR with about three hundred rounds through it. On the first string of fire only about 60% of my rounds went off. Panic flushed through my mind since I am also a brand spankin new reloader. I was sure I did something wrong. In my group was a certain hot rod revolver shooter and we took my gun to an empty bay to analyze my issue. The main spring screw had unscrewed it's self all the way to the grip. I guess a good dose of locktite is a good thing on even an unaltered screw.

Good thing I had a screwdriver and Gregg handy.

We won't talk about the overclocked barrel from the factory.

chris

[professor]

Most of the dirty work was done today. Only takes about 15 min. with a drill press and the proper taps (you should of seen the look on the shop owners face , he has a purdy collection of bone stock Rugers). I went all the way through so that I could put a set screw on each side of the strain screw then start the tap straight with the drill press turning only with yer hand. Once it's started Use an 1/8" bit with an 8/32 tap. The local hardware store only had allen screws that were double the length of what I had needed so I will grind them down tommrow and give this a try. The real acid test will be the range with Major PF loads, but I will post a follow up with more pics soon.

Uh... the double set screw installation increases potential for failure rather than decreasing it, compared to using just one set screw.

Follow this reasoning... or just jump to the last paragraph.

Base Case: You have a strain screw in a threaded hole, pushing against the mainspring. You have blue loctite holding that from loosening. Such installations have a certain potential to fail over time. The mechanism of failure is for shock/vibration of firing the gun to (1) crack the metal-loctite-metal bond, and (2) start the screw unscrewing due to the pressure from the mainspring each time the gun is fired once the loctite bond is broken.

Improved Base Case: The Base Case installation is strongest when the strain screw is made to exactly the right length, so that it can be screwed in solidly to the frame. Now, the head of the screw jams against the shoulder of the countersunk strain screw hole before the loctite is applied.

In ANY machine screw installation, there is clearance between the screw threads and the threaded hole in which it is installed. If this clearance is insufficient, you would not be able to screw in the screw. If this clearance is too generous, the sloppy fit doesn't provide any friction between the screw and the threaded hole, and the screw would immediately begin to back out of the hole. So we provide additional friction. When you screw the strain screw fully into the hole, you are pushing the screwhead against the countersink of its hole, AND you are pulling the threaded hole axially, so it is tight against the threads of the screw itself. Add loctite, and you've got a pretty good installation, that will last a long time.

But as we all recognize, it's a time-consuming, delicate process to get the strain screw to exactly the right length, and that doesn't last forever, as the tip of the screw gradually mushrooms against the mainspring, which acts the same as if the screw were backing out of the hole. That's why many of us want to work with a slightly longer strain screw, and hold it in place with a set screw... or two.

One Set Screw Case: So drill a hole from one side of the frame to the strain screw hole, and tap it for a set screw. Now, you just have to screw in the strain screw until it is just right, and then you screw in the set screw so that it pushes against the strain screw to stop it from rotating. Add loctite to both screws, and you're good for quite a while.

What's the potential for failure? Well, the strain screw is "loose" inside its threaded hole, except for loctite. This is the same as the Base Case. Only metal-loctite-metal bond inside the strain screw hole is preventing the screw from rotating out. The set screw ups the friction between the strain screw and the hole by pushing the side of the strain screw against the side of its hole. As you torque the set screw, you are also increasing friction between THAT screw and ITS screw hole. Loctite the set screw in place, and the Base Case is improved. Now, the set screw tip cuts into the strain screw, holding it in place through deformation of the metal. For this assembly to fail, the set screw-loctite-screw hole bond has to break, allowing the set screw to loosen/vibrate away from the strain screw. That lessens the force holding the strain screw against the side of ITS screw hole, reducing the friction holding it in place. Then the Base Case comes into play. You have reduced the potential for failure over the Base Case. However, without testing, you can't say for sure how much better this installation is than the Improved Base Case.

Two Set Screw Case: This installation will actually fail more rapidly than the single set screw installation. First of all, if the two set screws perfectly center the strain screw in its hole, then the friction between the side of the strain screw and its hole is ELIMINATED, as the strain screw is only being held between the two set screws, like it is caught by a set of pinchers. You've maximized the gaps, which means there is a thicker film of loctite between the strain screw and its hole than in the One Set Screw Case. Even if you crank down on one set screw, as if it is a single set screw installation, when you screw in the second set screw, any force you put on it will loosen the friction between the strain screw and its screw hole, AND loosen the friction between the OTHER set screw and its screw hole.

OK, so you've got loctite on everything. How does this fail? One of the set screws has to have its metal-loctite-metal bond broken. At that point, you might think that we're back to the One Set Screw Case, but actually, we've jumped directly to the Base Case, because loosening the pressure on one side of the strain screw allows it to move the same distance away from the other set screw! In other words, EITHER ONE of the two set screws loosens, we are back to the Base Case. In fact, using two set screws this way [directly opposed] roughly doubles the opportunity for the assembly to loosen, compared to the single set screw case.

Say one set screw bond will fail 10% of the time, over the course of firing 1,000 shots. A second set screw bond will also fail 10% of the time, during firing those 1,000 shots . That means that each set screw bond is expected to hold 90% of the time. But for the installation to hold, BOTH set screw bonds have to hold. The probability that both bonds will hold is the joint probability of each bond holding, or 90% times 90%, or 0.90 x 0.90 = 0.81. That means the 2 set screw installation is expected to hold 81% of the time 1,000 shots are fired, so it will FAIL 19% of the time. That's about twice as often as the single set screw failure rate.

Edited January 13, 2009 by professor

[Tom E]

Uh... the double set screw installation increases potential for failure rather than decreasing it, compared to using just one set screw.

Follow this reasoning... or just jump to the last paragraph.

Two things I don't think you took into account:

1. The stock strain screw is ridiculously soft. Witness the mushrooming of the tip. The threads are no better. Even when the strain screw is bottomed and the thread clearances taken up, the soft threads on the screw deform resulting in a loose screw. Not good in many contexts.

2. A set screw run into the stock strain screw from the side is really bothersome because it will deform the threads on the strain screw (junk strain screw, grade 8 set screw) and that can't be good for the threads in the frame when you take the strain screw out. Should work well though. Takes the thread clearance out by pushing from the side and cuts into (deforms) the strain scew threads creating mechanical interference.

In a way I wish I had never posted an opinion on this thread, but I still stand by my socket set screw with with 290 LocTite as an adjustable replacement for the stock strain screw. The next one I see that has come loose (or mushroom a tip) done this way will be the first and I have been doing this for 15+ years. Choose your own path, may it work as well.

Edited January 13, 2009 by Tom E

[Toolguy]

If you want to make the strain screw adjustable, the best way to do it is to drill and tap a hole from the bottom of the frame up

to intersect the original strain screw hole. Tap it for an 8-32 set screw and put a piece of 1/8 brass rod between the set screw

and strain screw so as not to damage the strain screw threads. Then the brass rod will push the strain screw sideways and

mesh it with the internal threads on the other side of the hole, giving a lot of contact area and keeping it from turning. The

strain screw can then be changed at any time by loosening the set screw, moving, and tightening the set screw.

[Tom E]

If you want to make the strain screw adjustable, the best way to do it is to drill and tap a hole from the bottom of the frame up

to intersect the original strain screw hole. Tap it for an 8-32 set screw and put a piece of 1/8 brass rod between the set screw

and strain screw so as not to damage the strain screw threads. Then the brass rod will push the strain screw sideways and

mesh it with the internal threads on the other side of the hole, giving a lot of contact area and keeping it from turning. The

strain screw can then be changed at any time by loosening the set screw, moving, and tightening the set screw.

I agree, but why bother if replacing the strain screw and using 290 LocTite works. 290 doesn't get dry and crumbly like the 242 blue. It retains considerable elasticity while preventing loosening.

[Toolguy]

Not everyone has a propane torch in their speeloader pouch.

[Tom E]

Not everyone has a propane torch in their speeloader pouch.

Whats that got to do with anything? Obviously you've never used 290 LocTite. LocTite products are not all the same. 290 wicks into assembled fasteneters and will seal porosity, it stays fairly flexible while retaining fasteners. You can turn a strain screw (stock or otherwise) without heating but it will keep it from loosening in service. Try it.

Edited January 13, 2009 by Tom E

[Toolguy]

I have used a lot of different Loctite products since they first came out. I have several on hand. One of them is 290.

It's green colored and has a watery viscosity. I have used it many times, but always had to heat it to undo, the same

as 262 red, or 680 green, or 545 thread sealant. The ones I have that will undo without heat are 242 blue and 222MS

purple.

[Tom E]

I have used a lot of different Loctite products since they first came out. I have several on hand. One of them is 290.

It's green colored and has a watery viscosity. I have used it many times, but always had to heat it to undo, the same

as 262 red, or 680 green, or 545 thread sealant. The ones I have that will undo without heat are 242 blue and 222MS

purple.

Mine (290) must be magic or I'm using it as intended and letting it wick in, not applying it before assembly.

[Toolguy]

As long as it does what you want, that's all that matters.

[Carmoney]

I started this discussion, and frankly I would like to end it with this--the bottom line: If you simply use the stock strain screw at a length that creates the correct amount of tension with whatever mainspring you're using, apply a little bit of blue loctite to the threads and then tighten it down as hard as possible with a screwdriver that fits properly, and you don't dick around with it, that screw will remain tight indefinitely. There will be no appreciable change in the mainspring tension, and your action should remain reliable for years and years and years.

[20nickels]

^^^^^ Well hang on there, I'm not quite done yet.... Had I to drill again I would have gone from the bottom up. Something I pondered before I started, but did it this way anyhow. This way I would not have had to chop the already short set screws shorter to fit in the narrow sides of the frame. Being a longer travel (bottom up) it would also allow more surface area for the screw to friction against.

The ace in the hole is a 1/16 pin I'm going to put through the new strain screw sideways as icing on the cake. The local hardware store will sell me all the 8/32 set screws I want if I decide I need to adjust tension or change springs. If that comes unscrewed I'll eat s*%#.

[jhgtyre]

^^^^^ Well hang on there, I'm not quite done yet.... Had I to drill again I would have gone from the bottom up. Something I pondered before I started, but did it this way anyhow. This way I would not have had to chop the already short set screws shorter to fit in the narrow sides of the frame. Being a longer travel (bottom up) it would also allow more surface area for the screw to friction against.

The ace in the hole is a 1/16 pin I'm going to put through the new strain screw sideways as icing on the cake. The local hardware store will sell me all the 8/32 set screws I want if I decide I need to adjust tension or change springs. If that comes unscrewed I'll eat s*%#.

There is indeed more than one way to skin a cat.

-ld

[Tom E]

^^^^^ Well hang on there, I'm not quite done yet.... Had I to drill again I would have gone from the bottom up. Something I pondered before I started, but did it this way anyhow. This way I would not have had to chop the already short set screws shorter to fit in the narrow sides of the frame. Being a longer travel (bottom up) it would also allow more surface area for the screw to friction against.

The ace in the hole is a 1/16 pin I'm going to put through the new strain screw sideways as icing on the cake. The local hardware store will sell me all the 8/32 set screws I want if I decide I need to adjust tension or change springs. If that comes unscrewed I'll eat s*%#.

There is indeed more than one way to skin a cat.

-ld

Yes, even if it's not Mike's way.

[JustinOGuy]

Im wondering what knuckling is and how the strain screw could cause it. Just found this article and read just nearly every word,, I got a lot out of it and plan on tuning my L frame 357 some..so, knowing how old this is,, Im not really expacting a reply, but if someone does,, Thanks..