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Thread: Firing Pin effect on ignition

  1. #1
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    Firing Pin effect on ignition

    Recently on 6mmBR.com I posted a 40x that I salvaged by taking a long action bolt and fitting it to the action. Then modifying the bolt body to take savage heads. In the thread I mentioned that the firing pin only have .125" of travel and .032" protrusion, I got a few responses that has made me curious. Most of the responses mentioned that the short lock time, even with constant ignition, wouldn't necessarily create uniform ignition, which would result in fliers. Even with the short pin fall, I have shot several small groups including one right at an inch at 400yds. I got so curious I made another firing pin for the rifle, with .200" pin travel and .052" protrusion to see if it made any difference.

    I guess I am asking what does the consensus here say about pin fall and protrusion? Do primer ignite in a uniform manner regardless the pin fall and protrusion?

    ** I can see excessive headspace playing a large role in this, but my cases are bumped back .002", not really allowing my case to run from the pin.

  2. #2
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    At a gun nut lunch meeting last Friday there was some discussion about firing pin travel and spring force. The firing pin spring can also be a factor in consistent ignition.

  3. #3
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    Firing Pin Protrusion

    didn't the pin with .052" protrusion pierce primers...???

  4. #4
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    Why would it? It is within the range considered normal. BTW I believe the usual consensus is that the primer stops the pin, not the pin shoulder, so protrusion should have nothing to do with piercing primers.

  5. #5
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    Quote Originally Posted by Boyd Allen View Post
    Why would it? It is within the range considered normal. BTW I believe the usual consensus is that the primer stops the pin, not the pin shoulder, so protrusion should have nothing to do with piercing primers.
    Interesting.... so... for the sake of discussion... a pin protrusion of 1/8" would be o.k.....................?????........in theory....????

  6. #6
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    I was reading about pin fall a few days ago. Found a pretty old thread where Joe Krupa was talking about pin fall. If I remember right he felt like .220" was what worked well for him. He changed triggers around until he found a combination that fit this parameter.

    I'll see if I saved a link to it.

    Found it about half way down http://benchrest.com/archive/index.php/t-84430.html

  7. #7
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    all of my guns are setup with protrusion of 50 to 60 thou. and FP fall somewhere in the .200 range.

    20-22lbs measured spring force.

    i'm sure you'll get replies from guys far more successful than myself, but i'd be willing to bet that this is the generally accepted norm.

  8. #8
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    Fwiw. ..I fought an accuracy issue for a whil, a few years back on a custom. Replaced spring, shot like a new barrel.

  9. #9
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    If you extend the tip of the firing pin and keep everything else the same, you decrease the firing pin fall, which may or may not be a problem, depending on what you started with, and how much you extend the tip. If you fire a primer, and measure the depth of the dent in the primer, from the case head (It would be best to use a tight fired case to do this.), you are very likely to come up with a number that is less than the protrusion of the pin from the bolt face...by a significant amount. Unlike most other actions, Savages have adjustable pin protrusion. Bob Greenleaf, retired from Savage where he worked as an engineer for many years, wrote that he set his at .035, well under what is considered "normal".
    Last edited by Boyd Allen; 09-24-2015 at 07:39 PM.

  10. #10
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    On this pin I shortened the OAL and the collar, this pin is fluted and i used a new spring. It'll be interesting to see the differance.

    Adam

  11. #11
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    This is based solely on anecdotal evidence from my own experience. I think that in actions that have a firing pin similar to a Remington's, anything less than .200 travel is a detriment.

    I also think you need a minimum 20 lbs of static spring tension. All of my Benchrest Rifles are at about 23 lbs.


    Protrusion? .045 seems about optimal.

  12. #12
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    Quote Originally Posted by B.Larson View Post
    I just asked an honest question......
    Mr Larson,
    Will your rifle pull your firing pin .125?

  13. #13
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    Quote Originally Posted by B.Larson View Post
    didn't the pin with .052" protrusion pierce primers...???
    Can someone just tell this man that firing pins aren't "pierced"......EVER???

    They're "blanked,"

    you can't "pierce" a primer cup with a firing pin.

    Even with 1/8" of fall.

    Turds in the catbox is one thing but this is just WRONG and takes from a good discussion.

  14. #14
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    gawd i love it when al wakes up!

  15. #15
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    firing pins

    I had a guy build a Remington 700 in 7 rum. He talked me into using a PGT bolt that was real close to the dia. of the raceway. It all sounded good, but he didn't check the protrusion of the firing pin. I shoot like crap and it took me a while to figure it out. I was sitting at the bench and decided to watch the bolt instead of the scope. I could watch the firing pin drop and decided to try it with another rifle as it seemed to me you shouldn't be able to see it hit the primer. I couldn't see it on the other rifle, it all happened too fast and recoil interrupted the eye sight. Greg Tannel fixed it and it shoots good now. Would a bunch of shots through the chronograph tell you if you have a problem? A short firing pin (at least in my gun) caused a hang fire. I don't know if your situation is the same, but I am sure the chrono would tell if you had a hang fire. Maybe also just inconsistent ignition?

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