638-3 Failure to Fire after many years

[BanditsRoost]

I'm stumped and looking for suggestions.
I've had my 638 J-Frame for many years with no problems. Now all of a sudden I'm getting light primer strikes.

I change the hammer spring several time using Wolff, MCARBO, Wilson and factory. I've tried a new factory, the #8, #8.5 and #9 from several different manufactures. I've installed the longer firing pin. Yet I still get regular light primer strikes. It's obvious the strikes are light. Two may fire fine with good hits then the next two hardly dent the primer.
(CCI 500) I'm no gunsmith but I can take the 638 to bare frame with no problems so replacing parts would be a breeze. Is there something else that could cause the LPS's?? I've even tried the hammer spring from my .22 J-Frame. Both old and new firing pins seem to move freely and are completely exposed with the hammer down and trigger pulled.

So now I'm asking the experts, any suggestions?

 

[rockquarry]

I'm far from an expert, but I've had very good results, including reliability, with most guns (including a 638) by leaving them as they come from the box. I'd send the gun to S&W and have them go over it and put it back as it came from the factory.

 

[BanditsRoost]

I'm far from an expert, but I've had very good results, including reliability, with most guns (including a 638) by leaving them as they come from the box. I'd send the gun to S&W and have them go over it and put it back as it came from the factory.

Thanks rockquarry,
S&W makes it plain. Since it has a Cerakote they have no suggestions or guarantees of repair. I've had excellent results on other J-Frames as well. That's mainly why I'm "stumped".
It has functioned properly for several years with the Cerakote. This 638 has less than 5k rounds on it since 1991. As mentioned, with all factory parts it has regular light primer strikes. I don't alter triggers on self defense firearms.

 

[kaaskop49]

Is a total of "less than 5K rounds" pushing it? That averages to less than 5 boxes a year over 20 years, but we're talking about an aluminum frame. Any chance the frame has stretched, thereby increasing the headspace? Not assigning blame here!

Kaaskop49
Shield #5103

 

[JimCunn]

Look for binding of yout hammer and mainspring. This doesn't sound like a firing pin problem.

 

[chief38]

The first thing I'd check is end-shake. This is when the parts are worn and the cylinder moves forward excessively - causing the firing pin to barley hit the Primers when the hammer falls.

If this is the cause it can be fixed with shims or stretching the Yoke.

 

[BanditsRoost]

The first thing I'd check is end-shake. This is when the parts are worn and the cylinder moves forward excessively - causing the firing pin to barley hit the Primers when the hammer falls.

If this is the cause it can be fixed with shims or stretching the Yoke.

Chief,
I've checked the "end-shake". (thanks for the correct term) It doesn't seem excessive to me. Barely even noticeable. I'll see if I can mic it. Is there a min/max I should look for?

 

[BanditsRoost]

Is a total of "less than 5K rounds" pushing it? That averages to less than 5 boxes a year over 20 years, but we're talking about an aluminum frame. Any chance the frame has stretched, thereby increasing the headspace? Not assigning blame here!

Kaaskop49
Shield #5103

I didn't think so, but again, I'm a shooter not a, smith. I'm certain I have more than that through a 642 and a Model 36. Though the 36 is steel. Is there a min/max dimension between the hammer nose bushing and the face of the cylinder?

 

[3rdgeargrndrr]

Hammer having signs of drag? Is it aligned straight without play?
the hammer spring strut in the correct slot on reassembly?
Lubed properly?

 

[3rdgeargrndrr]

Forgot to ask, is it only happening on a particular chamber(s)?

 

[L-2]

...and also look at one's ammo (reloading specs; components; settings).

 

[JDinAZ]

May have a dirty firing pin channel. Been known to cause intermittent light strikes in the 22s. Maybe a good qtip with solvent scrub in the hole and 100psi of air is worth a shot in your 38.

 

[chief38]

Chief,
I've checked the "end-shake". (thanks for the correct term) It doesn't seem excessive to me. Barely even noticeable. I'll see if I can mic it. Is there a min/max I should look for?

Use a Feeler Gauge to measure the barrel / cylinder gap both with & without pressure pushing rearward. See what the difference is. If it is a couple of thousandths you are ok. Some "slop" is necessary. If you have many thousandths (more than 3,4 or 5) I'd say that is excessive. Shims can be used inside the cylinder to reduce the difference, however doing that will also increase barrel / cylinder gap. Still, it is imperative end-shake is kept to a minimum. There is another method also that stretches the Yoke. Brownell's sells a tool to do that. It's sort of like a tubing cutter that scores the Yoke and stretches it a slight amount. Personally, I like the shims better.

 

[BanditsRoost]

Hammer having signs of drag? Is it aligned straight without play?
the hammer spring strut in the correct slot on reassembly?
Lubed properly?

Yes to all of those and not limited to a particular cylinder.


I may have found a clue though. I'll report back after the range today.......Don't think I've found the problem but maybe a temporary fix. Off to the range now.

 

[BanditsRoost]

Use a Feeler Gauge to measure the barrel / cylinder gap both with & without pressure pushing rearward. See what the difference is. If it is a couple of thousandths you are ok. Some "slop" is necessary. If you have many thousandths (more than 3,4 or 5) I'd say that is excessive. Shims can be used inside the cylinder to reduce the difference, however doing that will also increase barrel / cylinder gap. Still, it is imperative end-shake is kept to a minimum. There is another method also that stretches the Yoke. Brownell's sells a tool to do that. It's sort of like a tubing cutter that scores the Yoke and stretches it a slight amount. Personally, I like the shims better.

@Chief38,
The gap measures a snug .006" without pressure. With pressure it's not even .001" difference. IOW, .007 will not fit with no pressure. Earlier this morning with factory parts back installed it fired 20 rounds of Remington GW box with no issues....I'm loading 20 with Federal and 20 with Winchester and heading for the range. Doesn't make sense because I've been using CCI 500 for years with no problems.

 

[Bill In Texas]

Following, I have the same problem with a 637-2.

 

[jeffrefrig]

I believe it's about this time I start swearing at it! If and when you find the solution, could you please let me (us) know what you came up with for the repair, please? Good luck & God bless.

 

[BanditsRoost]

@Chief38,
The gap measures a snug .006" without pressure. With pressure it's not even .001" difference. IOW, .007 will not fit with no pressure. Earlier this morning with factory parts back installed it fired 20 rounds of Remington GW box with no issues....I'm loading 20 with Federal and 20 with Winchester and heading for the range. Doesn't make sense because I've been using CCI 500 for years with no problems.

Using DA all 20 of the Federal and Winchester fired no problem. The 10 Factory Remington and Blazer Brass fired fine. Four of the ten loaded with the CCI 500 failed to fire. Of those four, two fired on second strike using single action. SO, does anybody know the wall/cup thickness on CCI 500 Small Pistol primers? I'm showing .019" for the CCI and .015"-.018" on the others. Could one or two thousandths really make a difference?

I really appreciate all the help and suggestions. If nothing else I've learned some things. Nice Forum.

 

[BanditsRoost]

I believe it's about this time I start swearing at it! If and when you find the solution, could you please let me (us) know what you came up with for the repair, please? Good luck & God bless.

As many times as I've changed out rebound and main spring combinations now, I've had a few choice words flung about.

 

[BanditsRoost]

...and also look at one's ammo (reloading specs; components; settings).

@L-2,
You may have won the cigar.....see my last post.