What is the full benefit of bushing a firing pin?

Discussion in 'Gun Project Questions & Gunsmithing' started by Ledd Slinger, Jan 10, 2018.

  1. Ledd Slinger

    Ledd Slinger Gold $$ Contributor

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    I will be having a couple of my rem 700 firing pins bushed by Greg Tannel in the near future.

    I know that it helps to eliminate catering and piercing primers with hot loads. Also read it helps ignition and SD on speeds (not sure about the SD part because there's a lot of other factors involved there...)
    Does bushing a firing pin also help to prolong the life of primer pockets when running hot loads? I wouldn't think so, but thought I'd ask.
     
  2. Dusty Stevens

    Dusty Stevens COVFEFE Gold $$ Contributor

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    No it doesnt help the primer pockets. And if youre not blanking primers why worry about it?
     
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  3. Ledd Slinger

    Ledd Slinger Gold $$ Contributor

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    Take a look at these primers and judge for yourself if I should bush. The one on the bottom right even bulged around the crater rim. Some are so bad the rims cast shadows on the cups. Honestly don't know how I haven't pierced more at with the current charge weight. Primers are Fed 205.

    I did have one pierced primer blow out when testing max speeds. Backed the load off a few tenths so it's still a pretty hot load. I want to keep the load because the accuracy and tune is so good and the primer pockets hold up. But I would be a fool to keep shooting this load without bushing the firing pin.

    2018-01-10 20.30.59.jpg
     
    Last edited: Jan 10, 2018
  4. carlsbad

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

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    It doesn't change the pressure in the primer pocket so it doesn't affect primer pocket life. The reason the results are so much more improved is because the area is reduced (not the pressure).

    --Jerry 20171217_172524 (3).jpg
     
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  5. Ledd Slinger

    Ledd Slinger Gold $$ Contributor

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    Understood. Less weakened area of the primer cup surface area equates to greater strength for resisting back pressure
     
  6. carlsbad

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

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    Or another way to put it, the force pushing the firing pin back out of the primer is P x A = F. A = pi R^2 so the force goes as diameter squared. Reducing the bore from .080 to .062 reduces force by 40%.
     
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  7. Ledd Slinger

    Ledd Slinger Gold $$ Contributor

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    So basically due to the lesser force required to push the pin back...the cup doesn't encounter as much resistance and therfore does not create the crater around the pin?
     
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  8. carlsbad

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

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    Sorta. the cup doesn't push back, the pressure inside the case acts on the diameter of the firing pin hole. the firing pin force tries to keep the brass in place. So the force from the pressure in the casing (up to 60,000 psi) pushes the brass up, pushes the firing pin back (compressing the spring) and pushes a crater of brass up.

    Lets calculate the total force in a .080" hole at 60,000 psi. 60,000 x .08^2 x pi/4 = 75 lbs.
     
  9. Will Henry

    Will Henry

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    In many cases bushing the bolt face actually shortens case life because the shooter can now load to pressures which will expand primer pockets without cratering primers and if he can he will.
    I recently built a 30-338 for a friend and it was producing primers much like those shown above with loads which were only doing in the mid-2900's with 180's. I bushed the face and reduced the pin to 1/16" and the problem was solved. He dropped by later and mentioned he was having trouble with primers loosening. I asked about the load and he was now pushing 180's to 3240fps (all of this from a 24" barrel, by the way). I explained to him that 3100 was a hot load for the cartridge and maybe he should back off a bit. Uncharacteristically, he listened and has been a happy man since. WH
     
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  10. dsculley

    dsculley

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    I don't understand your equation. If the hole diameter is 0.080 then the radius would be 0.040 so the area would be 0.04² x π = 0.005 in². The pressure is 60,000 PSI so equation would be 60,000 x 0.04² x π = 60,000 lb/in² x 0.005 in² = 300 Lb. Did i miss something?

    With the 0.062 hole it would be 60,000 x 0.0305² x π = 175 Lb.
     
  11. DOGCAPPER

    DOGCAPPER

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    Your primers are suffering from enlarged pin hole.
    If you are going to push max loading pressure leave out the ejector when bushing the face. More surface for pressure distribution.
    Another annoying hole for brass to flow into closed off.
     
  12. AckleymanII

    AckleymanII Silver $$ Contributor

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    I fall into this catagory. Also, every 257 Weatherby I have ever had has cratered primers, I just ignored the crater.
    So, I hunt down the toughest brass available, and If I can get 150-250 fps which just happens to be the next accuracy node, to heck with the brass. I would buy some 7MM mag RWS brass, neck up to 30 and rock on...it is a hunting rifle.

    The next option would be to use a Neil Jones hand decapper or a Harvey Deprimer(http://harveydeprimer.com/) and deprime on a seperate operation, tossing the loose primer pocket hulls as the Rockwell hardness will vary up to 6% on various lots of brass of the same lot#, depending on the brand.

    3250 fps out of a 30/338 Winchester, all I can say is Wow-this sounds like a way over the top load, this is about what they get out of a 30 STW.
     
    Last edited: Jan 12, 2018
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  13. watercam

    watercam Gold $$ Contributor

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    One other excellent plus with Greg's work is that he creates a funnel shaped interior guide so that the firing pin does not drag on the sides of the pin tunnel.
    Hard for me to describe but the firing pin is guided for all of it's travel. This became a real benefit with my .223 Palma rifle which had excessive ES/SD numbers which improved quite a bit after bushing.
     
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  14. Ledd Slinger

    Ledd Slinger Gold $$ Contributor

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    This is what I do except I use the Frankford Arsenal hand depriming tool. I find that depriming as a separate operation helps to identify loose or loosening primer pockets BEFORE you attempt to seat a new primer in the case. Plus it's nice when I'm depriming hundreds of varmint rounds. Just hang out on the couch and watch hunting shows, Street Outlaws, or The Curse of Oak Island while I do it :)

    Disadvantage of the Frankford hand tool is it does not have PPC flash hole option. Advantage is that it can deprime fired 20 cal cases. Most universal depriming dies and hand tools only deprime down to 22 cal. Gotta have a good firm handshake to use the Frankford ;)

    http://www.cabelas.com/product/FRAN...hpnlhnKj_3omsdsPN3MaArpYEALw_wcB&gclsrc=aw.ds
     
  15. carlsbad

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

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    Not quite right...

    The interior is not funneled. It is reamed to a specified diameter. The entry is funneled, at least it is on my design and I think Greg does it too. The big improvement that greg (and I) do is to lengthen the guide bushing so that on cock, the tip of the firing pin does not exit the guide channel. it is always guided.

    I'm pretty sure this is what you were talking about.

    --Jerry
     
  16. carlsbad

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

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    You are absolutely correct. The calculator on my laptop was giving me fits and I did the math wrong. I used "Pi d squared over 4" instead of "pi R squared" same formula but my calculator let me down. I can't get ascii functions to work either. --Jerry
     
  17. swadiver

    swadiver Silver $$ Contributor

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    I use the Franklin tool as well. i just turned down the decapping pin in my drill press and it decaps BR cases fine now
     
  18. Ledd Slinger

    Ledd Slinger Gold $$ Contributor

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    How is it holding up? Still plenty of strength? I was gonna 'dissect' the tool and see if I could figure out how to make smaller PPC replacement pin.
     
  19. swadiver

    swadiver Silver $$ Contributor

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    holding up fine with lots of use. very easy to remove the pin and chuck it in the drill with some fine sandpaper. took me five minutes. you can can also get additional pins from Franklin Arsenal i believe
     
  20. Ledd Slinger

    Ledd Slinger Gold $$ Contributor

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    2018-01-11 18.35.44.jpg

    Very simple to remove. One Allen set screw in the back and the decapping pin comes right out.

    It's all one piece. I'll see if i can find another to purchase and turn down. Maybe call Frankford. I would like to maintain the original pin for strength because I sometimes buy cheap once fired 223 brass for my 20 TAC. If the primers are crimped, they can be stubborn when trying to remove them. If I can find another one, I'll just turn it down for the PPC flash holes and swap the pins out as needed. I'd imagine the pins must be available somewhere because they are obviously built as a replaceable component on the tool.
     

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