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Discussion Starter · #1 ·
Hi all,

I have a newish 610. I'm fiddling with the mainspring and the strain screw (nevermind that), trying to get the lightest DA trigger pull possible while still getting affirmative primer strikes.

Load, shoot, remove grip, adjust screw, replace grip, load, shoot, remove grip, adjust screw, replace grip, repeat...

Stupid question... Rather than using live ammo, couldn't I simply use primed empty cases to test whether the gun is hitting the primers hard enough?
I would be using empty .40S&W cases with moon clips, so headspace or the fit of the cartridge in the chambers would be a non-issue.

That would save me a bunch of fiddling at the range... I figure I could do it in my backyard.
 

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You might want to dedicate a few pieces of brass for this use by drilling out the flash hole to 1/8". The pressure normally generated by a fired round pushes the case back against the frame so the primer can't back out. Without that pressure the primer could back out a bit and tie up the gun or make it hard to open the cylinder.
 

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You might want to dedicate a few pieces of brass for this use by drilling out the flash hole to 1/8". The pressure normally generated by a fired round pushes the case back against the frame so the primer can't back out. Without that pressure the primer could back out a bit and tie up the gun or make it hard to open the cylinder.
I loaded some 38 specials with just a primer and a wax bullet I made. I found that the primers will indeed back out and could cause a problem. i took some 38 and 357 brass with split necks and cut them off shorter to eliminate the crack then drilled out the flash hole to eighth inch and they worked great
 

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First,
Get a new strain screw.
In other words, your screwing yourself by messing with it.

2nd,
Buy Kuhnhassens book.

3rd,
Read it.

Theres a few things that can be done, by a novice to improve the DA.
None of it involves the strain screw or the sear of either SA/DA.
A few tools, reading that book will do far more good, than messing with a strain screw.
 

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You can adjust a strain screw by filing the tip of it or getting a different length, but it still has to be screwed in tight.

Just reduce the rebound spring a pound or two and leave the mainspring and screw alone.
 

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I have used seated primers to test guns and I never had the issue with popping primers but in reading the recommendations above .. it makes perfect sense to create less pressure by opening the flash hole.

Thanks guys for the tip!!
 

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Discussion Starter · #8 ·
I found that the primers will indeed back out and could cause a problem...
OK!

I have thousands of rounds of brass .40 cases, which I'm probably never going to use (I also have thousands of nickel cases, which I do us), so sacrificing several dozen by drilling out the flash holes is easy...


You can adjust a strain screw by filing the tip of it or getting a different length, but it still has to be screwed in tight.
Right, I have a couple spare strain screws, and I have a bunch of 8-32 set screws with the nylon locks...


First,
Get a new strain screw.
In other words, your screwing yourself by messing with it.

2nd,
Buy Kuhnhassens book.

3rd,
Read it.

Theres a few things that can be done, by a novice to improve the DA.
None of it involves the strain screw or the sear of either SA/DA.
A few tools, reading that book will do far more good, than messing with a strain screw.
Right... I'm sitting here with extra screws and Kuhnhausen's book (note the spelling!) opened to page 81.
 

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Or, use a "ballistic pencil"... or "ballistic chop stick"....

Just cock the hammer, moving the cylinder into position, insert the eraser end of the pencil down the barrel (or a chop stick) and release the sear. Watch how much force the pencil or chop stick is ejected with. Either fire it up (watch your eyes) or against a piece of paper on the wall from a fixed distance.

To protect the barrel from the metal eraser mount, you can put shrink wrap tubing around the metal.
 

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Discussion Starter · #10 ·
Or, use a "ballistic pencil"... or "ballistic chop stick"....
Yes, but my problem is that I'm getting intermittent failures to fire due to light primer strikes... I can see where the firing pin is dimpling the primer, but not hitting it hard enough to set it off.

Another stupid question: Is there some way to measure firing pin protrusion w/o special tools?
 

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Discussion Starter · #11 ·
Another stupid question: Is there some way to measure firing pin protrusion w/o special tools?
Nevermind... I figured it out: Cylinder out, cylinder latch rearward (!), cock hammer, and then push.

No offense to Kuhnhausen, but it's obvious that he wrote for "revolversmiths" with fully equipped workshops, and not hobby DIYers who need to improvise!
 

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If you don't at least have a trigger pull scale you are just pushing a rope uphill. The strain screw is the final step in a process that involves internal work, testing, possibly replacing springs and more testing. You are most likely better off returning your revolver to the stock configuration.
 

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Discussion Starter · #14 ·
If you don't at least have a trigger pull scale you are just pushing a rope uphill.

Don't worry, I do... A nice Wagner force gauge.

I know I only have several dozen posts on this forum, but I'm a really good reader!

Thanks, everybody, for the good advice. I just drilled out the primer pockets of 3 dozen .40 cases to make "blanks."

Back to firing pin protrusion: Kuhnhausen seems to say that S&W's stock protrusion isn't enough, and more is better, so I'm going to install the Apex pin that I picked up a while ago.
 

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Discussion Starter · #16 ·
OK, it worked... I measured the length of the strain screw (beyond the frame, 0.102"), removed it, replaced it with the set screw, and then tightened that significantly less tight (.075").

My new "blanks" fired 6/6.

So I backed off the set screw a half turn (which visibly radically changed the tension of the mainspring) and got only 3/6 to fire.

I turned it back in a quarter-turn, and it went 6/6. Then 6/6 again. Then 6/6 once more with the grips on.

The DA trigger pull is much much MUCH lighter and nicer now!

Also, shooting "blanks" in the garage is a blast! I aimed at one of those "grill pad" things, and I'm glad I did, because otherwise I think I would've burned a hole in the carpet. I wore ear-pro, but the "blanks" were quiet enough that my wife and daughter inside the house (attached) don't seem to have noticed...
 

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If you haven't done it already, be certain to somehow mark or alter those casings that you drilled out the primer pockets so they can't be used for live fire ammo.
I would recommend cutting them all 1/2" shorter than they already are. That way you will know they're altered casings.
Or, be certain to throw them away just as soon as you're done testing with them.
 
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I wonder if everyone is missing the elephant in the room. Maybe the answer is in your first post.
MODEL 610
Being a rimless cartridge both 40 and 10mm can easily suffer what can best be described by headspace issues including light primer strikes.
Often reliability is subject to the brand/style of moon clip.
I see the answer being the textbook reason they make a longer firing pin.
With a longer pin you may get the option of both lighter springs / trigger pull and reliable ignition.
Just look for pierced primers and be ready to trim the pin if needed.
 

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Short story on the OPs primer test on cking spring mods.
First pistol I bought at 15yrs old was a Colt Diamondback. Reading period gun magazines(along w car Mags)
and Nontes Pistolsmithing book among others back then (early 70s)
trick was to use a nail to stretch the
mainspring (V type spring) to lessen the trigger pull. Testing w my handloads using a Lee powder scoop
dipper setup then shot and found my nail stretching the spring produced misfires. My past LEO dad ( S&W guy) fussed bout my messing up my
new Colt.
So I puzzled back then and unknown to parents after school I tested primed only cases sooting them down our hallway Bout 15 ft thru the house after school before the got home..
Playing w mainspring tension got me reliable strikes back on the primed only cases.
This post reminded me 50 yrs later of my early endeavor to learn about revolvers and why after yrs of various builds of diff types Im back to my first love revolvers.
Only vintage S&Ws nowadays.
 
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