Firing Pin Spring Pressure

[STS]

Do any of you gentlemen have any experience directly measuring firing pin spring pressure? What fixture is used to measure it. I've been around this game for 45 years and I have NEVER seen a method of accurately measuring spring pressure. I'm interested in learning more about it.

 

[STS]

It would appear no one knows any more about the subject of firing pin spring pressure than I do. Which is very little.

 

[Dusty Stevens]

Every gunsmith i know uses a bathroom scale. Keep it simple.

 

[WayneShaw]

Every gunsmith i know uses a bathroom scale. Keep it simple.

Any scale that will read to 30 pounds+ will work. I use a piece of 2x2 wood with a hole drilled for the firing pin tip to fit in so I'm not pushing on it, then pull down the shroud until you reach the cocked position, read pounds.

 

[carlsbad]

I have measured spring rate and posted about it here. What I used was a long rod the inside diameter of the firing pin. I put it in the vice. I made a washer in the lathe to sit on top of it. Then I started loading weights on top of it. The weights can be any round weight with a hole in the middle that will fit over the rod and sit on the washer.

Spring rate is k in the equation F=kx. so if 20 lbs of weight compresses your spring 1", your k is 20lb/in.

So load enough weight to get the spring compressed to approximately to it's captured length on the firing pin. This weight is irrelevant as it just gets the spring into the condition it is installed in the rifle, and it may be quite a bit of weight. Add another 10 lbs and measure how much more in compresses. Use a dial indicator and measure very accurately.

k=F/x or the weight your added divided by the compression difference.

--Jerry

 

[BoydAllen]

I think what most are interested in is the weight at cocked length, not the rate. Personally, I use a bathroom scale and a block of wood with a hole big enough so that the pin rests on its flange. I note the position of the cocking piece in the shroud when the action is cocked and push down on the shroud (block on scale, pin in hole in block) until the position of the firing pin looks the same. Before I start I note the reading from the weight of the block and FP assembly, and subtract that from my total. None of this is ultra precise, but I am not sure that it has to be.

 

[STS]

If a spring is said to be a 22 pound spring is that at "captured" length or "cocked length"? That is the question that I was trying to figure out the answer to.

 

[carlsbad]

Then you can use the rig i described to determine how much weight it takes to get to the cocked length.

Don't be surprised if your results are different than advertised. Spring weight is not simple to maintain consistent manufacturing results, especially in relatively stiff springs. Metallurgy is part witchcraft.

--Jerry

 

[Robert]

I used to place the scale on the drill press table (or the vertical mill, placing the decocked firing pin unit over the scale,using a drilled sleeve bearing against the FP shoulder protect the tip.

Applying the quill pressure on the shoud just enough to clear the sear from its resting position gave the decocked spring force.

Moving down the quil up to the normal cocked position gave tne cocked force.

As Carlsbad said, readings can be interesting to compare with original datas.
R.G.C

 

[Alex Wheeler]

I feel like compressing the spring on a scale is pretty accurate as my number jive with Borden's. They dont with most others. Most are lighter than advertised when I check them. Rate on most springs is not a problem, theres one action out there I know of that its is IMO.

 

[Robert]

I feel like compressing the spring on a scale is pretty accurate as my number jive with Borden's. They dont with most others. Most are lighter than advertised when I check them. Rate on most springs is not a problem, theres one action out there I know of that its is IMO.

Alex,
I think (FWIW) that the spring should be compressed sufficienty or just be a little over its maxima force lenght (L1) when in decocked position. In this condition,there is no increase of weight when cycling the bolt, one of the conditions for a smooth opening.

This also ensure constant force during FP travel.

This condition is not always achieved, reason why I think measuring in both positions is recommendable.

R.G.C

 

[Concha]

http://www.thewellguidedbullet.com/pdfs/FiringPinImpactStudies.pdf

 

[johara1]

I measure pin fall then measure weight on an old Atlas drill press that I mount an indicator on the side. I have two delrin blocks to protect the pin assembly zero it out on the scale and compress it to the exact pin fall I have recorded earlier........ jim

 

[Alex Wheeler]

Alex,
I think (FWIW) that the spring should be compressed sufficienty or just be a little over its maxima force lenght (L1) when in decocked position. In this condition,there is no increase of weight when cycling the bolt, one of the conditions for a smooth opening.

This also ensure constant force during FP travel.

This condition is not always achieved, reason why I think measuring in both positions is recommendable.

R.G.C

I measure in the cocking and fired position. Most of the time the difference is not enough to consider. In one action however I lost 5 full pounds. Short springs are worse. When working with a normal sized action and a normal spring you wont have any rate problems. I dont recommend trying to play with lighter springs to ease bolt open, too many accuracy issue are caused that way.

 

[STS]

Information started off a little slow here but we have fleshed this thing out pretty well. Some different techniques to measure pressure and some info on performance. It seems that pin fall trumps spring weight but you still need adequate spring pressure. I wonder how much degradation of the spring can be tolerated. I have a pretty good coyote rifle that I built that will shoot sub 2 inch groups at 500 yards with a 50 year old firing pin spring.

 

[Dusty Stevens]

Information started off a little slow here but we have fleshed this thing out pretty well. Some different techniques to measure pressure and some info on performance. It seems that pin fall trumps spring weight but you still need adequate spring pressure. I wonder how much degradation of the spring can be tolerated. I have a pretty good coyote rifle that I built that will shoot sub 2 inch groups at 500 yards with a 50 year old firing pin spring.

Weight trumps pin fall to me. Ive seen groups get cut in half on factory sporter rifles with no other change than replacing a lightweight firing pin assy with a factory solid steel one. Its one thing the extreme accuracy gunsmiths really work on. inertia.

 

[Alex Wheeler]

Weight, spring and fall. No reason not to have them all.

 

[STS]

Anyone think the inertia can be excessive? Too much of a good thing so to speak.

 

[Alex Wheeler]

I have went past the point of practical, and no. Not within reason.