Strain screw???

[toad67]

Going to order a few extra parts to have around, including strain screws for various model/frame sizes. Looking at MGW, they have screws listed as fitting K/L/N, 629's as well as straight N frames, blued and S/S. Not sure why a screw would be model or frame size specific if they list some as fitting K/L/N.
Gunparts also has some listed, but they list them from the gun they came off of. Looking to have a few on hand for testing, as well as replacement as necessary.
Some guidance as to what to purchase would be appreciated, thanks.

 

[StrawHat]

If you need a strain screw, use an Allen screw. The headless type can be shorten until they disappear in the grip strap.

Kevin

 

[chief38]

If you need a strain screw, use an Allen screw. The headless type can be shorten until they disappear in the grip strap.

Kevin

While you are correct in that Allen Head Screws can be used (thread wise), it just goes against my grain to use the wrong type of screw when the original type is readily available. This is a screw that once fit and properly tightened will most likely rarely be removed so the head type doesn't much matter for practicality purposes . An Allen screw in a vintage Smith would keep me up at night! - LOL.

 

[chief38]

Going to order a few extra parts to have around, including strain screws for various model/frame sizes. Looking at MGW, they have screws listed as fitting K/L/N, 629's as well as straight N frames, blued and S/S. Not sure why a screw would be model or frame size specific if they list some as fitting K/L/N.
Gunparts also has some listed, but they list them from the gun they came off of. Looking to have a few on hand for testing, as well as replacement as necessary.
Some guidance as to what to purchase would be appreciated, thanks.

When they originally printed the "instructions and parts list" (4 page, one piece that came with vintage Smiths) they probably listed the Strain Screws as different parts numbers for each revolver. The original lengths might have varied depending on caliber and grip frame. Today, they are pretty much all the same length and must be fit to the individual model - at least that has been my experience. The 8x32 slotted screw has changed a few times over the years, even when I used to buy them directly from S&W. They used to come with an oval tipped and contoured end and that is the style I like the best, even if I modify them.

While a continuous thread 8x32 screw will also work fine, (the thread must be non distorted & perfect on the ground end if ground down as to not mess up the revolvers frame threads - hence the non threaded domed end on the originals) I like to keep the screw type as they would have used back when the revolver was built - but that's just me.

 

[StrawHat]

…An Allen screw in a vintage Smith would keep me up at night! - LOL.

The stuff which nightmares are made!

Kevin

 

[toad67]

When they originally printed the "instructions and parts list" (4 page, one piece that came with vintage Smiths) they probably listed the Strain Screws as different parts numbers for each revolver. The original lengths might have varied depending on caliber and grip frame. Today, they are pretty much all the same length and must be fit to the individual model - at least that has been my experience. The 8x32 slotted screw has changed a few times over the years, even when I used to buy them directly from S&W. They used to come with an oval tipped and contoured end and that is the style I like the best, even if I modify them.

While a continuous thread 8x32 screw will also work fine, (the thread must be non distorted & perfect on the ground end if ground down as to not mess up the revolvers frame threads - hence the non threaded domed end on the originals) I like to keep the screw type as they would have used back when the revolver was built - but that's just me.

What exactly does one need to do to fit it correctly? I understand that grinding it to fit, if it's to long, but how does one know if it's to long or short?

 

[Green Frog]

If it goes in deeply enough, the leaf mainspring will produce sufficient hammer power to strike primers reliably for consistent ignition. Going deeper just makes your double action pull harder. You’ll know the screw is in too shallow when you get misfires due to weak hammer fall. It’s a narrow window.
Froggie

 

[stang1911]

.605" OAL and .480" under the head for square-butt, .505" OAL and .380" under the head for round-butt. Your Welcome

 

[dfariswheel]

Jack First Gun Parts sell most all sizes and types of S&W strain screws. Usually $7 to $9 a screw, depending on type and blued-stainless.

 

[ArchAngelCD]

Why not just call S&W and buy parts you need from them?

I bought a pre-model 10 and a few of the screws looked wrong. I called S&W and they connected me to pasts and they sent me all the screws so I can replace them all with the correct ones. (no guessing, they know what you need lol)

I don't remember what I paid but I do remember thinking, that's not a bad price...

(USA) 1-800-331-0852
Monday-Friday 8:00AM-4:45PM EST

 

[chief38]

What exactly does one need to do to fit it correctly? I understand that grinding it to fit, if it's to long, but how does one know if it's to long or short?

The generic length screws sold now are usually ridiculously long and will produce trigger pulls heavier than what you are trying to improve. I believe the source of where they come
from will greatly matter as well. Back in the old days, everyone got them directly from S&W. Today strain screws are produced by different manufacturers and do vary quite a bit.

The screw must be fit so that ignition is 100% reliable and so there is no hammer push-off. You can also “read” the primer strikes to make sure they are adequately deep enough. You can also use a trigger pull gauge to monitor your work. Remove very small amounts at a time and check the results often. You should shoot CCI primed ammo as they are considered the hardest to detonate and you want only 100% ignition 100% of the time.

Many years ago I developed a feel for what is right and it’s impossible to translate a feel in a post. I’d suggest getting a bunch of screws and proceed slowly. Test with live ammo at the range and make sure all primers have good hits. Any screw that has been shortened too much-discard! Save the original screw so it can always be put back if the gun is sold or gifted. I would never want an accident or situation to occur to someone else from something I did-let the next owner determine what’s right for them.

Again, the answer to your question is when the gun is 100% reliable with a lighter and smoother pull. Sorry I can’t be more precise but this is something you have to feel and test personally. Also, make sure the screw is tightened when all is said and done.

What I will say is that you could TEMPORARILY back out the original and test it - then when you’ve determined the right length. You can see just how many threads to remove on the new screw. Get a bunch - this way you will have enough to make the perfect one without fear of messing up your only one!

I like to finish the end that contacts the main spring just like the original domed screw. I sometimes even blue them when done. Just makes me feel a professional job has been done.

 

[DVCBILL]

I had to shorten a few of the screws lately. An easy way is to chuck the head up in a cordless drill and spin it while running a file across it. You can shape the tip any way you want like with this method.