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t0066jh

Light strikes with a PC 627? How to diagnose and fix?

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Today I had 5 or 6 light strikes out of 275 rounds shot out of my 627.

So here's my list of checkpoints and what I've found so far.  Any suggestions are welcome.

1.  High primers.   The gun has around 10k rounds thru it. No light strikes until recently.

2.  Loose strain screw.   Nope. It's seated all the way down and lock tighted.

3.  Loose cylinder.  Added an .002 and an .003 shim which seemed to cure the problem for a while.

4.  Extended firing pin.  Have tried both Apex and Cyl and slide extended Firing Pins.  Forget which one is currently installed.

5.  Main Spring. Light main spring was installed with original trigger job by first owner.

 

Thanks in advance for any suggestions.

Joe

Edited by t0066jh

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If reloads, possibly a few primers didn't get seated as firmly as the rest. You don't say what primers you are using, or what the hammer pull is. The setup might be on the edge of what the primers need to set them off. You can make the hammer hit harder by bending the mainspring backward a little, if that's what is needed.

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Federal Primers.  Case gauge them one at a time.  Checking primers on every one........still possible to miss one not fully seated.  When you say hammer pull are you speaking of trigger pull double action and single action?  If not how do I measure hammer pull.? 

Hammer is stock. 

Is there a technique for bending the mainspring.  I figure I'd set it on edge and trace the current curvature and then bend a little at a time.

 

Edited by t0066jh
didn't complete my post.

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Your mainspring could be replaced. I would also pull out the firing pin and double check it. I saw a 627 recently that started getting light strikes. Turned out the firing pin was broken in half but still working (somewhat). 

Could be an ammo issue too. No way to know except by process of elimination 

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For hammer pull, cock the hammer and hook the trigger pull gage under the ledge on the front of the hammer. Gently let the hammer down till the hook on the pull gage is resting on the frame. Then pull the gage and read the ounces of pull when the hammer just lifts off the frame. This tells you how much tension the mainspring is exerting on the hammer. You can adjust up or down from there and find the weight at which you are getting no misfires. You may want to record that number. You can then find the best rebound spring to go with the hammer weight. You can use a #8-32 x 1/2" socket set screw to find the best hammer tension, then blue Loctite it or make a regular strain screw the right length to give the same tension. This way you have a measurable, repeatable way to know where you're at. Otherwise you are just guessing.

Edited by Toolguy

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18 hours ago, Toolguy said:

For hammer pull, cock the hammer and hook the trigger pull gage under the ledge on the front of the hammer. Gently let the hammer down till the hook on the pull gage is resting on the frame. Then pull the gage and read the ounces of pull when the hammer just lifts off the frame. This tells you how much tension the mainspring is exerting on the hammer. You can adjust up or down from there and find the weight at which you are getting no misfires. You may want to record that number. You can then find the best rebound spring to go with the hammer weight. You can use a #8-32 x 1/2" socket set screw to find the best hammer tension, then blue Loctite it or make a regular strain screw the right length to give the same tension. This way you have a measurable, repeatable way to know where you're at. Otherwise you are just guessing.

 

Checked the hammer pull weight.  3 tries all came back at 4.25 lbs with a Wheeler spring gauge.  

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So, thank you all for the input and plan to check out these items one at a time to isolate the problem. To bad I don't have a range out my back dooor.

I checked my spent brass and light strikes  (5 of 280 rounds).

Strain screw is tightened all the way down and hasn't moved from the lock tighted condition

  Fired rounds have a semi-deep firing pin mark that is uniform on all fired pieces. Checked all of my loaded ammo looking for high primers.......none

Compared cylinder fit to my newer 627 that was sent as a replacement for one with a cracked area near the crane.  The new gun cylinder is very tight with a very slight rub on the frame when closing the cylinder and not as smooth to open as Problem gun.   Problem gun has no such rub and is much easier to open.  Added a .002 shim to the .003 shim put in by my gunsmith.  Now have a tighter fit.

Test fire next before doing any other changes.

 

More later.

Edited by t0066jh
spelling/grammar

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I have not checked fitment.  Still new to working on the gun myself other than changing a few parts.  What would I be checking for.?

 

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10 hours ago, Alaskan454 said:

If you've added shims to the cylinder you can eliminate play there.  With the cylinder closed see if you still have movement.  If you do it's possibly from extra room where the yoke screw makes contact.  You can buy shims for both here: https://www.triggershims.com

 

I'm using your shims placed in the front of the cylinder and there is no movement.  Are these different shims and where would they be inserted?  The screw on the side plate (is that the yoke screw?) is fully seated and lock tighted.  

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If you have 4.25 pounds on the hammer gage, that should crush any primer out there. That is way heavy. There must be something blocking the hammer fall. Hold the top of the hammer all the way down in the fired position to see if the trigger has any front to back play. If not, the hammer is hitting the rebound slide just before it hits the primer and the rebound slide and spring are softening the blow to the firing pin. This often happens when a trigger stop is installed.

Edited by Toolguy

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In a recent thread, somebody had light strikes on a different revolver model, depending on which brass and which moon clips were used.

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5 hours ago, t0066jh said:

 

I'm using your shims placed in the front of the cylinder and there is no movement.  Are these different shims and where would they be inserted?  The screw on the side plate (is that the yoke screw?) is fully seated and lock tighted.  

The screw on the side plate which has the internal plunger is the yoke screw.  I also agree that 4.25 pounds of hammer force is seriously heavy, mine is quite a bit less than that.  Which brands of brass had light strikes? Also, what kind of moonclips are you using?  Warren's advice is solid, check for interference of any kind in the action.  Also, if your cylinder is tight the likely culprit would be moonclips and brass. 

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58 minutes ago, Alaskan454 said:

The screw on the side plate which has the internal plunger is the yoke screw.  I also agree that 4.25 pounds of hammer force is seriously heavy, mine is quite a bit less than that.  Which brands of brass had light strikes? Also, what kind of moonclips are you using?  Warren's advice is solid, check for interference of any kind in the action.  Also, if your cylinder is tight the likely culprit would be moonclips and brass. 

4

All brass is  Starline Short Colt.  As mentioned before, my spent brass all looks the same with a semi-deep strike in the center...except for the light stikes.

I appreciate all of the suggestions and will follow the advice if the shim addition does not solve the problem.

 

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Correction to my previous post.  Still learning correct nomenclature.  The shims have been placed on the yoke, not the cylinder.

 

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1 hour ago, t0066jh said:

Correction to my previous post.  Still learning correct nomenclature.  The shims have been placed on the yoke, not the cylinder.

 

No worries, what brand and thickness are the moonclips?

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Even if the strain screw hasn't backed out the tip of it can deform which reduces tension and, if you are living on the edge of reliability, cause light strikes.  This happened to me during a match and someone suggested slipping a spent primer cup (minus the anvil) over the end of the strain screw.  We did this without removing the strain screw by taking the mainspring off of whatever you call that part that connects it to the hammer, sliding the primer cup onto the strain screw, and then replacing the mainspring.  It was kind of a pain in the rear to do but it worked and I finished the match without further problems.  Once back home I bought a new strain screw.   This same fix would add extra tension to a mainspring that was either worn out or had been bent too far.

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3 hours ago, Alaskan454 said:

No worries, what brand and thickness are the moonclips?

a mix of TK, Hearth and some from a local provider with a high-end CADCAM machine.  (sells them through Dillon Precision).

 

One other thought was from a friend that said I might be short stroking the trigger.  Would that mess with the timing?  The light strikes are still dead center.

Edited by t0066jh

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3 hours ago, t0066jh said:

a mix of TK, Hearth and some from a local provider with a high-end CADCAM machine.

...

 

Is there any difference in strikes between the different moonclips?

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13 minutes ago, perttime said:

 

Is there any difference in strikes between the different moonclips?

 

Spent brass strikes are all very similar .  The same is true with the light strike unfired rounds.

Test firing tomorrow and a 250 round match.  Hopefully the additional shim is the solution.  The first shim was a solution a year ago.

 

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Keep on mind, the primer and case set back upon firing making the firing pin strike look larger. Your actual firing pin strike is what you see in the light strikes.

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When you mentioned putting a shim on the Yoke, exactly where did you put it? There is one where the yoke goes into the frame, this increases headspace, thus reducing the firing pin blow, there is also one that goes into the cylinder where the yoke is inserted into it, this pushes the cylinder towards the frame, reducing headspace and increasing firing pin blow.

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The extended firing pin usually accounts for all the minor variations mentioned, such as moonclips, primer seating, yoke position, headspace, etc., etc. The massive hammer spring tension should overcome all of this more minor stuff. These are typically the things you look at when you have a light mainspring setting and are trying to maximize reliability.  How you pull the trigger does not enter into this equation.

 

I think there is something interrupting the hammer fall. Can't tell what, without seeing the gun. Maybe hitting the rebound slide, the lock is popping up, the hammer block is not always getting out of the way, who knows.

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I don't know if it is relevant, but I had a similar situation with my 625.

 

Kept track of moonclips, headstamp, etc., no common thread.

HOWEVER, it seemed to happen with light loads and long shooting sessions.

Best I could figure, the light loads didn't expand enough, and I got fouling that (slightly, almost imperceptibly) impeded chambering. So the firing pin strike just finished the chambering. The 'light strikes' fired on second attempt.

I now just brush the chambers (dry) when I'm shooting high round counts of light loads, and I haven't had a recurrence.

 

Hope it helps, if it does thanks goes to the guy shooting a 686+ that told me about his similar issues.

 

John

Edited by JDMahan
Auto correct induced typo

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