Normal Hammer block contact? Model 36

[Matt_X]

J-frame hammer springs

Quick update:

Thank you Mercury!

The new black spring is slightly longer. If everything else is the same as the old black spring (and it seems very close), then assuming a modulus of elasticity of 12x10^6, the spring rate of the old black spring is around 13 lb/in, new spring is around 14 lbs/in. That could be the difference between using a good vernier vs. a cheap dial caliper. However the new one's free length is longer, so it will apply more force for any given compression.
The spring rate of the new silver spring calculates to be closer to 17.5 lbs/in. Length is between the old black and the new black.

I bought a good used round stirrup/hammer strut. Installed that with the new black spring. Also took a one little burr off the side plate where it was just scratching the hammer. But that won't effect the weight test.


Testing the result of the spring change using the same method as previously posted, result was only another ounce at best. So its up to 59 oz.

However, the difference between primers firing and not firing has been the difference between single action and double action. The static force as measured doesn't change between SA and DA. So its a good reference point, but doesn't tell the whole story.

Next step will either be to test the installed spring and stirrup with the Fiocchi, or change to the silver spring and measure the hammer force. Depends on whether I go to that range before I get time in the shop.

 

[Matt_X]

Fiocchi .38 spl

Annecdotal but perhaps indictive of harder primers.


Two reviews of Fiocchi 130 gr FMJ at Lucky Gunner have failures to fire. Both were using S&W Model 19. Total of about 8 reviews that state or suggest the person had actually used the ammo at time of review.

 

[Protocall_Design]

The spring wire diameter makes a big difference, too. A couple thou. larger wire diam. will be a lot stronger spring, all else being equal. If all the springs have equal wire gauge, they will be essentially the same.

 

[Mercury]

You're welcome Matt_X, I'm happy to help.

I included the 2nd silver-colored spring because it felt stiffer and you may end up needing a stronger one.

If it where mine, I wouldn't feel that it was fixed until it had zero failures-to-fire, so range testing is necessary.

Please continue to keep us posted and good luck.

 

[Matt_X]

The bright spring certainly has the highest spring rate and will apply more force through the working range. At some point I will try it just because I'm curious if it will have any noticible impact on the trigger pull.

My measurements for working range of spring are as follows:
Hammer in rebound 1.322"
Hammer at Single Action full cock 0.984"
Hammer fully forward (with no cartridge) 1.347"


The wire of the old hammer spring was 0.033" dia. and the wire of the new black spring is about the same (as mentioned I don't fully trust the dial caliper I have at the house). The wire of bright spring measures .0345 but I think its .035" wire. This because .033 and .035 are standard piano wire diameters.

The other difference of note is the the black springs have 27.5 coils while the bright spring has one less coil. Other differences are minor. For example the ends are cut and ground although the new black spring end is more tapered than the other two.

 

[Matt_X]

Range Test

Summary: Seems to work.


The range still had Fiocchi but now only 130 gr. FMJ.
Primers seem to be the same type.


Cylinder = 5 cartridges
First two cylinders had one failure to fire each.

Each cartrige that failed to fire double action on the first try did fire on the second try double action.
At this junction I was getting ready to try some Precision One brand with CCI primers, but figured 10 rounds is not enough to get a sense of the percentages.

Cylinders 3 and 4 had zero failures to fire. This is interesting.
The next two cylinders were shot offhand double action and were also fine. OK. This seems promising. Lets keep going.
Target out to 17 yards, and the remaining 20 cartridges all went bang on the first pull of the trigger (yes double action).


I took a look a photo of the primers when they all went bang, and one looks like a light strike. Looking through the box of spents shells and there are a few more like this. I think this is a hard primer. Also maybe the hammer nose strikes just enough off center (low) that maybe its even harder to dent that location.

So the bottom line is that now it seems to be working. I think the revolver is just on the edge of setting these primers off consistantly. Will need to put a more Fiocchi through before I'm convinced.

 

[Protocall_Design]

Looks like a borderline, barely enough hammer strike.

 

[Matt_X]

Everything the same other than the cartridge manufacture. This time it was Browning and Winchester (latter shown in photo).

 

[armorer951]

Sorry, but can you refresh my memory as to whether or not you test fired it without the hammer block installed?

I'm still stuck on the hammer block or "hammer hits rebound" interference scenario.

thanks


Carter

 

[Matt_X]

Sorry, but can you refresh my memory as to whether or not you test fired it without the hammer block installed?

I'm still stuck on the hammer block or "hammer hits rebound" interference scenario.

thanks


Carter

Yes. I tried it without the hammer block and had failures to fire. (back in post #28)

Today I wanted to try cartridges that are known for having normal primers. Comparing the indentations on these with the Fiocchi in the posts above, I think Fiocchi's primers are harder metal.

 

[armorer951]

I'm most puzzled by the 'inconsistency' of the primer hits in your photos. It seems very odd. When clean, and in spec (correctly fit with unaltered factory parts) the revolver should fire any non-defective commercially produced ammunition without failures.....zero.

I'm wondering about the headspace, and the integrity of the cylinder assembly fitment, the extractor, the yoke fitment, and the hammer nose/rivet. I guess you've ruled these things out as contributors?



Carter

 

[Matt_X]

With the honing and new hammer spring there haven't been any more failures to fire even with the Fiocchi after those first two mentioned in my May 12 post.
@Protocol_Design said the firing pin marks on the Fiocchi primer cups still looked light. I think he also stated the hammer spring force of 59 oz. is marginal. I gather there is no published spec for J-frames, so this is based on his experience.

I do agree that the hits seem a little inconsistant. I think the firing pin hits a little bit to the right. The nose itself shows slightly uneven machining. Changing the firing pin myslef is a bit smithing I want to get into - especially since I'm not sure it would change anything. But this, plus the side contact of the hammer does suggest this was a more marginal build than typical.

from my notes the cylinder to barrel clearance is .007 to .0085" with a .002" cylinder bearing washer installed.
The headspace is around .063- .064
There is one .002 hammer shim installed on the right side.

I didn't check the alignment of the chambers to the barrel but bullets hit close to center. My groups yesterday where not great but no obvious flyer gun issue (at least not obvious to me)

 

[Matt_X]

30 rounds of Magtech 158 gr double action followed by 20 rounds single action and no failures to fire.

Same spring (for now). Did change back to target stocks, which seems to help my shooting. That's another area of further testing.



Over in the M&P subforum there are comments about ,380 Fiocchi ammo issues. This only futhers my beleive their primers or at least some of their primers are harder than other manufacturers.

 

[steelslaver]

Have you checked your hammer nose stick out. Open cylinder and press thumb piece back so you can cock and fire the hammer. hold the trigger back and look at the tip of the hammer nose (firing pin) sticking out. It should stick out the thickness of a dime.

 

[Matt_X]

Have you checked your hammer nose stick out. Open cylinder and press thumb piece back so you can cock and fire the hammer. hold the trigger back and look at the tip of the hammer nose (firing pin) sticking out. It should stick out the thickness of a dime.

Yes. Used a stack of feeler gages - easier to hold than a dime.
.044 to .045"
Jerry K wrote he measured .039 - .048 and Carter here posted .045 - .050 is OK.

What has happened is that I haven't had any reason or chance to shoot Fiocchi and its worked fine otherwise. So its been on to other projects. At some point I would like to install the shiny spring to see how it effects trigger pull and hammer force.

Maybe I'll take it with me to the range this week. They had some blue box Fiocchi my last visit, which shot fine out of my Model 15. Frankly I was glad to see it rather than the Magtech.

Post in thread 'Normal Hammer block contact? Model 36'

Mar 6, 2024

Have you ever checked to see how far the hammer nose sticks out of the recoil shield with the hammer all the way down? It should be around .050, about the thickness of a dime. Variations in rim thickness, primer seating depth, endshake, etc, can become a problem if there is not enough protrusion.

Yes. Firing pin protrusion is around .044 or .045" (comparing with feeler gages). Khunhausen wrote that he has measured .039 to .048" so it seems one is close to factroy maximum. (He also suggests .055 to .062 max should be good, but I infer that is if one is replacing the...

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