Firing pin bushing issue

Discussion in 'Gun Project Questions & Gunsmithing' started by hunter686, Jan 11, 2019.

  1. hunter686

    hunter686

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    Hi all,

    I have decided to bush the firing pin hole on my "Custom action" that I've had for just over a year. I've had primer issues since day one all the way through the pressure curve and deciced to pull the bolt apart and do some checks to find out what i was dealing with.

    Having mic'd and clocked all the internal parts of the bolts and firing pin i have run into a few issues:

    • The firing pin hole is off centre by .2mm which when chucked up and examined is very noticeable. I'm not too bitter about this as bushing it properly will sort this. Not the most impressive for a £1500 ($1923.26) action though...

    • Firing pin/hole tolerance: Having mic'd the firing pin and pin gauged the holes there sizes are 0.067 for the pin and 0.072 on the firing pin hole leaving around 5tho of clearance. This is where i think the main issues of the crating is coming from and as far as i'm concerned significantly more than it should be.

    • Bent firing pin: This is the part that is causing me the biggest issue. If you look along the pin itself there are at least 3 separate cutting operations leaving 2 obvious parallels that are nowhere near each other in terms of concentricity. i.e half moon cuts along the pin assembly . There is also significant run out over the 5mm end section of the pin its-self that you can see in the images. I have attached 3 images; One of the bolt in a "true" section of the bolt about 0.0024mm or 0.0001" runout. (This is the closest i could get without actually taking the time to adjust it) and then showing the bent pin. The very end of the pin showing almost dead nuts with the true section. But when you move 5mm up the pin this thin opens out to 0.01mm or 0.0004' 3tho run out in the space of 5mm. I drilled a sample 0.067" hole in some hardened steel to see how the pin would clear and sure enough the pin binds around 1/3 - 1/2 down.
    Any suggestion on how to approach this? Obviously with the assembly being bent the pin needs significant clearance in order for it to work but this leads me back to square one. One thought is to precision grind the whole pin down to 0.062 and go from there. Or, manipulate the pin to relieve the warp? Any advice is much appreciated.

    Thanks in advance
     

    Attached Files:

    Last edited: Jan 11, 2019
  2. BIG D

    BIG D

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    I personally feel that if you spend that kind of money on something it should be right. Therefore with that being said, most companies that manufacture these high dollar actions will usually make it right at no cost to you other than one way shipping. Just my .02
     
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  3. carlsbad

    carlsbad Lions don't lose sleep over the opinions of sheep. Gold $$ Contributor

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    Off center is not unusual and probably not a problem unless you have cratering. bushing may or may not fix this depending on the rest of the geometry of the bolt.

    gap between firing pin and hole has little impact. diameter of hole is what matters. .072 is getting close to OEM rem diameter of about .080. Bushing to .062 will probably fix your problem.

    Firing pin sounds like it should be replaced. Hopefully this custom will use a remington 700 pin which is easily available from JGS.
     
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  4. spclark

    spclark Gold $$ Contributor

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    Do you know if bolt’s been hardened? Bushing one that has been will be trickier than if not; one respected bushing ‘smith here in US won’t touch hardened bolts.

    Given what actionmaker priced yours at I’d certainly make the first call to them for a resolution.
     
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  5. butchlambert

    butchlambert Site $$ Sponsor

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    Remember, He lives in Scotland.
     
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  6. TAJ45

    TAJ45 Gold $$ Contributor

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    Action maker probably has some one supplying his f pins. Regardless, I would think the action mfr would be beyond willing to "make it right".
    However, I know nothing of import regs of "gun parts" if mfr was not in the Isles.
     
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  7. hunter686

    hunter686

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    I have just written a thousand word email to the guy with all the DTI and runout pictures. Fingers crossed he is civil about it and fixes it. I want to give him the chance to make it right before making something like that public, You know!?

    I have pretty bad cratering and about a 2% miss fire rate on the primers that i am running. This may not be related but its worth noting. A replacement pin is all good and well but i don't want to put any carbide near the bolt if i know there is a chance it could get taken care of. As i'm going to have to bush the bolt one way or another.


    The body is 17-4PH but i'm not too sure about the bolt it's self. 17-4PH comes in at around 34HRC i believe. I don't fancy trying the file test on it find out just yet though ;) RPMs and carbide will get through most things if all else fails but like i said i'd rather is was sorted by the OEM before i jig er up in the CNC and starting making chips
     
    Last edited: Jan 11, 2019
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  8. hunter686

    hunter686

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    I orientated the pin slightly to show a better comparisons:
     

    Attached Files:

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  9. Evlshnngns

    Evlshnngns

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    I think Carlsbad nailed it. Sounds like a good time to go down in diameter.
     
  10. Ggmac

    Ggmac Gold $$ Contributor

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    That's not a firing pin , it's a camshaft .
     
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  11. RWO

    RWO

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    17-4PH comes in a range of hardness. In the USA, a common heat treatment for rifle receivers is condition H1025. This gives about RC 38, still easy to machine, especially with carbide. I doubt the off-center hole is causing a problem since it is only .008" ( .2mm) off. However, I doubt very much that the bolt is 17-4PH. If the OEM won't fix it, I would make a new firing pin out of 4140HT or S7 that fits the existing hole nicely and I bet that solves the problem.

    RWO
     
  12. hunter686

    hunter686

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    That's some good info there. Making a new pin I don't think would be an issue. It's pretty basic by the looks of it. The only issue I think I'd have would be the radius at the end of the pin. I may aswell be hung for a sheep as a lamb and go for the full hog and knock it down 0.062" along with pin hole while I'm at it. Any other farm animals I can throw in there?...
     
    Last edited: Jan 11, 2019
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  13. ronemus

    ronemus Silver $$ Contributor

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    If there is one that will fit, this might be a good time to put in a SpeedLock firing pin. An aluminum body with steel tip & sear makes it much lighter so the fall is much faster; that helps to get reliable & consistent ignition. It made a world of difference in a Mauser - the factory pin was a bus! It's much better than trying to correct tyhe botched pin you have.
     
  14. carlsbad

    carlsbad Lions don't lose sleep over the opinions of sheep. Gold $$ Contributor

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    I can't see the scale on your indicator very well. Does that pin really have .085 tro?

    Cratering and misfires don't usually go together so I'd say you have more than one problem. The bent pin may be causing the misfires.

    --Jerry
     
  15. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    The problem with a bent firing pin is drag. If your not experiencing drag you may not have an issue. What you should be after is a guided pin along its travel without drag, a full weight spring and pin. A .062 pin will cure cratering issues and you can use an 8-40 screw to bush with. No matter the cost its rare to buy a perfect action. Good on you for actually checking it out.
     
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  16. DaveTooley

    DaveTooley Silver $$ Contributor

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    If you make a new firing pin don't use a full radius on the tip. That aids cratering. You want a flat with a slight radius on the edge.
     
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