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Question on firing pin protrusion.

This is a discussion on Question on firing pin protrusion. within the The M14 forums, part of the M14 M1A Forum category; The slam fire thread got me thinking on something that is beginning to wear at the back of my little head. With our m2 based ...


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Old August 20th, 2012, 10:10 PM   #1
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Question on firing pin protrusion.

The slam fire thread got me thinking on something that is beginning to wear at the back of my little head.

With our m2 based machine guns we have a gauge that appears identical to the one fulton list for the m14 except for its size of course. It has two sides. One for "go" and another for "no go". with the m2 bolt out of the machine gun and with the mechanism "fired" (firing pin protruding from bolt face in t-slot) we run the "go" side of the gauge up and down the t-slot and it should freely pass over the firing pin. Thats how we know that the firing pin is not protruding too far. Conversely the "no go" should catch on the pin so that we know it protrudes far enough. A firing pin that protrudes too far can pierce primers or become damage / broken, and a firing pin that doesn't protrude far enough may fail to actuate the primers.

Now when I relate this to my m14 I immediately thought that with a free floating firing pin that the overall length of the pin and the protrusion dimenstions could feasibly, uh, lets say aggrevate, any issues with poor quality ammo that could lead to an issue such as was brought out in that slamfire thread.

In the m14 / m1a can a firing pin protrude too much? What if the overall length of the pin is too long? I see that fulton sells a firing pin protrusion gauge but how is it used?

As far as our m2's go we routinely gauge them, approx once a month and after every range session.

Is this something that I need to do with my m14? Do I as an owner and operator need such gauges like a firing pin protrusion guage or firing pin hole gauge? Or is this something that i should trust my gunsmith to do when i bring my rifle to him if i ever notice a malfunction? Also just because I am not noticing an issue doesnt mean that the rifle doesnt have one.

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Last edited by CNelson; August 21st, 2012 at 05:06 AM.
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Old August 20th, 2012, 11:01 PM   #2
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Quote:
Originally Posted by CNelson View Post

In the m14 / m1a can a firing pin protrude too much? What if the overall length of the pin is too long? I see that fulton sells a firing pin protrusion gauge but how is it used?

Is this something that I need to do with my m14? Do I as an owner and operator need such gauges like a firing pin protrusion guage or firing pin hole gauge? Or is this something that i should trust my gunsmith to do when i bring my rifle to him if i ever notice a malfunction? Also just because I am not noticing an issue doesnt mean that the rifle doesnt have one.
I have inspected thousands of GI M14's and their related parts. I have never known a good condition GI bolt and FP that allowed too much FP protrusion BUT notice I mentioned "good condition." We used/use the same FP Protrusion Gage on both the M1 and M14.

To use the gage, you place the assembled bolt in your hand and apply forward pressure on the back of the firing pin tail. You run each side of the gage notiches over the protruding tip of firing pin while you hold the flat side against the face of the bolt. On the minimum side, the FP nose should not allow the gage to pass over the FP nose. On the maximum side, the notch should pass over the FP nose wthout being stopped.

If you get into changing bolts and FP's and ESPECIALLY if you are using commercially made bolts and firing pins, then yes you should have one of these gages. Factories and Armorers/Gunsmiths who work on M14's MUST have one of these gages, but not the average civilian.

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Old August 20th, 2012, 11:30 PM   #3
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Gages are the quick way when doing multiple bolt assemblies, but direct measurement ought to work as well for the occasional inspection.

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Old August 21st, 2012, 12:06 AM   #4
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what length range is in tolerance?

is that known?

if not just what is the spec?

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Old August 21st, 2012, 02:30 AM   #5
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.044 min .060 max.

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Old August 21st, 2012, 08:18 AM   #6
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Quote:
Originally Posted by jmoore View Post
Gages are the quick way when doing multiple bolt assemblies, but direct measurement ought to work as well for the occasional inspection.
I agree with this, but only when the person has precision measuring instruments and good working experience at using them. For a machinist, that's no problem, but for the average guy, it is far better and cheaper to buy and use the gage.

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Old August 21st, 2012, 08:36 AM   #7
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Thanks guys. Gus I kinda figured that on how gauge was used. However I was unsure if another tool was required to hold the firing pin in the fired (extended, protruding) position. In our machine guns we have an integral spring contained in the rear portion of the firing pin extension that drives the pin forward against a stop. Once the sear is tripped it stays in the fired (extended) position until it is cocked again by moving the cocking lever. With the free floating firing pin of the m14 I was unsure if hand pressure alone at the back would suffice to get an accurate measurement on the other end of the pin at the bolt face. I also agree that for most users the gauge would more than suffice and would keep things simple.

However I have convinced myself that for home use, I do not require the gauge. With that said, should I encounter any issues I would probably obtain a gauge (beg, borrow) before deciding to swap firing pins. To make sure the original pin was defective and that the new pin meets specifications. I would also probably gauge the firing pin hole in the bolt face at that time as well.

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Old August 21st, 2012, 10:36 AM   #8
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Here is information for many:

M1 & M14 .044------------.060



M16 .028-----------------.036



M60 .035----------------------.043



.30 BMG .060------------.068



.50 BMG M2 .073-----------.080



M203 G/L .032------------------.047


Last edited by Bill Ricca; August 21st, 2012 at 10:39 AM. Reason: Changed Format
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