N-Frame strain screw length?

[orionengnr]

I recently purchased an M-25-2 round butt. It has had the barrel shortened to 3 1/2 inches and apparently had an action job done. The trigger is very nice but when shooting double-action it misfires about 50% of the time (same with or without moon clips). When shooting single action it is fine. I took off the grips and the strain screw looks as if it "may" have been shortened.

I compared it with my 25-5 (square butt) and the screw on the 25-2 is noticeably shorter.

Numrich calls out one part number for the round butt and another for the square butt strain screws.

At long last, my question: does anyone have the correct dimension for the length of an unmolested N-frame round butt strain screw?

I don't want to replace it unless it is the problem. Also, I don't know if any springs were replaced--should I be talking with Wolf, or should I try swapping the main spring from my 25-5?

 

[orionengnr]

I recently purchased an M-25-2 round butt. It has had the barrel shortened to 3 1/2 inches and apparently had an action job done. The trigger is very nice but when shooting double-action it misfires about 50% of the time (same with or without moon clips). When shooting single action it is fine. I took off the grips and the strain screw looks as if it "may" have been shortened.

I compared it with my 25-5 (square butt) and the screw on the 25-2 is noticeably shorter.

Numrich calls out one part number for the round butt and another for the square butt strain screws.

At long last, my question: does anyone have the correct dimension for the length of an unmolested N-frame round butt strain screw?

I don't want to replace it unless it is the problem. Also, I don't know if any springs were replaced--should I be talking with Wolf, or should I try swapping the main spring from my 25-5?

 

[RufusG]

That's funny. I have a 25-7 with a shortened barrel that works with LC but not with ACP in DA (it's cut for moonclips). Last week I measured a few screws because of this. The one that wouldn't work was .505". Four other N's I measured were between the low .560"'s and .592" (longest was a 1917 with a heavy trigger, other three were in the .56-.57-something inch length). HTH

Edited to add: All the ones I measured were square butts.

 

[tomcatt51]

An easy way to check is to get an 8-32 set screw (socket style are best they're grade 8). Put it in instead of the stock strain screw and you can adjust your mainspring tension. No screw head to limit how far you can screw it in. Easy way to test. I use them instead of the stock strain screws, notch the socket end slightly for reference (so you can put it back together the same way) and put a drop of 290 Loctite on to hold them in place. A length between 3/8" to 1/2" works depending on your mainspring and grip frame. They also fix the "misfire problem" some people have with the Wolff reduced power mainsprings which isn't a spring problem, just a (too short) strain screw problem.

 

[Raider]

Now this is a VALUABLE post. I had the same short strain screw problem with my RB mod 25. I ordered a RB screw from GPC; they sent me a SB screw whose head is too big to enter the frame.

Many thanks for the answer to my question too.

 

[judge]

Sir - A new sq butt screw is aprox .613 length and the round butt screw is .503 length. Measured total overall length. Note - this may change on the newer model guns. The figures quoted are the older model (60's, 70's, 80's)

 

[R-Tex]

Originally posted by tomcatt51:
An easy way to check is to get an 8-32 set screw (socket style are best they're grade 8). Put it in instead of the stock strain screw and you can adjust your mainspring tension. No screw head to limit how far you can screw it in. Easy way to test. I use them instead of the stock strain screws, notch the socket end slightly for reference (so you can put it back together the same way) and put a drop of 290 Loctite on to hold them in place. A length between 3/8" to 1/2" works depending on your mainspring and grip frame. They also fix the "misfire problem" some people have with the Wolff reduced power mainsprings which isn't a spring problem, just a (too short) strain screw problem.

I agree 100% with Raider - that's an absolutely wonderful hint! Falls in the category of, "Now, WTH didn't I think of that?"

I knew I was hangin' out with some smart folks!

Thanks very much, tomcatt51.

 

[orionengnr]

Judge--
Thank you. That is exactly the information I was looking for. My screw is .407, obviously about 1/10th of an inch short.
I will try to find one locally (and the set screw idea is a good one, if I can find one that is 1/2 inch long or so); if not I'll be contacting S&W, Numrich, etc.

The amount of knowledge available on this site is amazing. I thank you all, and will report back.

 

[orionengnr]

And I reallylike the set screw idea. Now where do I find hex head set screws of 1/2" and greater length?

Note to self: hit Home Depot tomorrow

 

[eddieb]

Originally posted by orionengnr:
And I reallylike the set screw idea. Now where do I find hex head set screws of 1/2" and greater length?

Note to self: hit Home Depot tomorrow

I picked up a 1/2" and 3/4" at Lowes today.

 

[bountyhunter]

On the three model 66's I have with the Wolff ribbed spring, all developed occasional light strike misfires over time after the curved rib "coned off" the head of the strain screw from turning it in and out ( which effectively shortened it). I took a small file and shaved the inside egde of the strain screw's head enough to get an extra 1/4 turn of insertion depth and that fixed it.

 

[tomcatt51]

Originally posted by bountyhunter:
On the three model 66's I have with the Wolff ribbed spring, all developed occasional light strike misfires over time after the curved rib "coned off" the head of the strain screw from turning it in and out ( which effectively shortened it). I took a small file and shaved the inside egde of the strain screw's head enough to get an extra 1/4 turn of insertion depth and that fixed it.

If the alloy/heat treat of the stainless strain screws wasn't junk quality that wouldn't happen.
Use the strain screw for a blued (not stainless) gun or a socket set screw and that problem goes away. I've seen the SS strain screws mushroomed so badly the tip had to be filed down before they could be screwed out of the frame. One recently was a dead stock unmodified 625-3.

 

[bountyhunter]

Since they are model 66's, they came with stainless strain screws. All the SS parts (including the gun itself) seem softer than blue steel, that is one of the disadvantages of using stainless. The formulae of stainless that are harder generally rust more.

I have found that once the screw head cones against the rib of the Wolf mainspring, then the full face surface of the screw tip is rubbing on the mainspring surface and it doesn't wear as much after that.

I realize I could keep putting in new screws or use a different kind with no head. I like having one that tightens down against the frame because it is unlikely to walk.

 

[orionengnr]

Note to self: hit Home Depot tomorrow

I picked up a 1/2" and 3/4" at Lowes today.

Dang, went to Home Depot and found 1/2" only. Not sure how hard they are; if they "mushroom" after installation then I have a new problem. Guess I'll be ordering the proper blue, hardened screws from Numrich.

 

[tomcatt51]

Originally posted by orionengnr:

Note to self: hit Home Depot tomorrow

I picked up a 1/2" and 3/4" at Lowes today.

Dang, went to Home Depot and found 1/2" only. Not sure how hard they are; if they "mushroom" after installation then I have a new problem. Guess I'll be ordering the proper blue, hardened screws from Numrich.

If it's a socket set screw, set screw that uses an allen wrench instead of having a slot for a screwdriver, no "head", it's grade 8 (hard). If it's slotted for a screw driver it may not be grade 8 but will still be way harder than a S&W SS strain screw. You should be fine. 290 Loctite is desireable to hold it in place. It wicks into assembled fasteners. After you get it assembled and adjusted how you want it, put a drop on the threads on the spring side and let it wick in.