How to measure light strikes?

[shooting on a shoestring]

I have a Model 60 in .38 SPL from the 70's. Its a high mileage specimen. A couple of years ago it came out of time, gap was too big, I sent it back to S&W. They set the barrel back, recut the forcing cone, replaced the hand (for less than $100). When it came back it was on limited duty as my primary CCW had become an SP101.

Over the past several months I've had it at the range for a few sessions (I love to shoot it) and got a couple of light primer strikes in DA. I chalked it up to a tired main spring until last night.

I popped the side plate for a look inside (hadn't done that since its return from S&W). It was very clean, lubed in the right spots and dry in between. However, the lube on the hammer pivot seemed thick and gummy. Also the main spring guide rod was slightly gummy dragging against the main spring. I pulled the hammer out cleaned the pivot and hammer, then applied some castor oil with a toothpick to the pivot and mainspring guide rod, and the side of the hammer where it appears to drag against the frame.

After putting it back together, I wondered, is there was a way to determine, or measure the force the firing pins applies to the primer?

My first idea was to drop a drafting pencil (no earaser but a metal cap over the back end of the pencil) down against the firing pin bushing and pull the trigger. The distance the pencil was ejected would give an indication of the firing pin force. I compared the Model 60s distance to that of the SP101. Shooting the pencil up, both strike the ceiling. Shooting level (held against a vise, not 100% accurate but pretty close), pencil travel was with in a foot and approximately 10 feet down range.

At first I thougth, well the Model 60 is striking with roughly the same force as the SP101, but then it dawned on me, not necissarily so. In an actual firing, the firing pin contacts the primer and may drive the shell a few thousandths into the chamber until the rim stops it. Then the shell and cylinder will procede forward until the cyclinder travel is stopped. These both absorb momentum. So if the cylinder travel (end shake) is greater, and/or shell end clearance/travel is greater, then the firing pin force will be retarded.

Anyone have an idea of how to measure or at least compare actual (useable) firing pin striking force?

[44man]

I have a Model 60 in .38 SPL from the 70's. Its a high mileage specimen. A couple of years ago it came out of time, gap was too big, I sent it back to S&W. They set the barrel back, recut the forcing cone, replaced the hand (for less than $100). When it came back it was on limited duty as my primary CCW had become an SP101.

Over the past several months I've had it at the range for a few sessions (I love to shoot it) and got a couple of light primer strikes in DA. I chalked it up to a tired main spring until last night.

I popped the side plate for a look inside (hadn't done that since its return from S&W). It was very clean, lubed in the right spots and dry in between. However, the lube on the hammer pivot seemed thick and gummy. Also the main spring guide rod was slightly gummy dragging against the main spring. I pulled the hammer out cleaned the pivot and hammer, then applied some castor oil with a toothpick to the pivot and mainspring guide rod, and the side of the hammer where it appears to drag against the frame.

After putting it back together, I wondered, is there was a way to determine, or measure the force the firing pins applies to the primer?

My first idea was to drop a drafting pencil (no earaser but a metal cap over the back end of the pencil) down against the firing pin bushing and pull the trigger. The distance the pencil was ejected would give an indication of the firing pin force. I compared the Model 60s distance to that of the SP101. Shooting the pencil up, both strike the ceiling. Shooting level (held against a vise, not 100% accurate but pretty close), pencil travel was with in a foot and approximately 10 feet down range.

At first I thougth, well the Model 60 is striking with roughly the same force as the SP101, but then it dawned on me, not necissarily so. In an actual firing, the firing pin contacts the primer and may drive the shell a few thousandths into the chamber until the rim stops it. Then the shell and cylinder will procede forward until the cyclinder travel is stopped. These both absorb momentum. So if the cylinder travel (end shake) is greater, and/or shell end clearance/travel is greater, then the firing pin force will be retarded.

Anyone have an idea of how to measure or at least compare actual (useable) firing pin striking force?
Castor oil is a very poor choice. It will gum up the works again. Use a good gun oil.

[shooting on a shoestring]

44man - You're right. I did that out of shear laziness as it was close at hand (and I was a bit curious) and I planned to be back in there soon to replace the mainspring. I typically use light motor oil for long term inside lubrication.

I suppose that could be another thread: what constitutes good lubrication inside a gun.

[Mk42gunner]

I have worked on K, L, and N frame S&W's not tooo many J frames. That said: is there any way you can hook a scale on the hammer, or otherwise measure the strength of the mainspring?

I would hope that the techs at Smith & Wesson checked the mainspring while doing all the other work that you listed, but things happen.

Robert

[arcticbreeze]

I have worked on K, L, and N frame S&W's not tooo many J frames. That said: is there any way you can hook a scale on the hammer, or otherwise measure the strength of the mainspring?

I would hope that the techs at Smith & Wesson checked the mainspring while doing all the other work that you listed, but things happen.

Robert

Sure you can with the correct tool but I would think that if that was my suspect it would be cheaper to just order a main spring from Brownells and just rule it out.

[shooting on a shoestring]

Ran a handful of rounds through the Mod 60 today. No light strikes, all primer dents looked good. Guess it just needed some lubrication. I'll clean out the castor oil and lube it up with light motor oil. When I get a round to it, I'll get a new mainspring just b/c I should.

[Glen]

Just use a trigger scale to weigh the force needed to get the hammer cocked fully.

[Frank]

How about use the Lee Hardness tester viewer to measure the primer crater?

[Ricochet]

Castor oil is a very poor choice. It will gum up the works again. Use a good gun oil.
+1. I once lubed up my 1911 with castor oil, and it was the slickest stuff ever when fresh. I had trouble reassembling it because the barrel link pivot pin kept falling out from its own weight. But that stuff turned into glue in a few months. Won't come out with petroleum based solvents, either. Lacquer thinner works well.

[shooting on a shoestring]

Frank - Yep, I think dropping the hammer on primed cases w/o powder or boolit, then measuring the crater is a great idea.

The problem with just focusing on the hammer, is that doesn't account for the force lost in moving the cylinder and cartridge forward.

Thanks Frank.

And thanks to the 1st hand accounts concerning the perils of using castor oil for gun lube. I did it as a temporary lazy fix, it'll be corrected this week.