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lug Contact %

This is a discussion on lug Contact % within the Gunsmithing forums, part of the M14 M1A Forum category; I started lapping in a Fulton bolt today. What percentage of contact would you say this is? I am guessing 30 to 40% ?...


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Old March 19th, 2017, 04:02 PM   #1
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lug Contact %

I started lapping in a Fulton bolt today. What percentage of contact would you say this is? I am guessing 30 to 40% ?
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Old March 19th, 2017, 05:37 PM   #2
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Quote:
Originally Posted by mb3 View Post
I started lapping in a Fulton bolt today. What percentage of contact would you say this is? I am guessing 30 to 40% ?
What are you shooting FOR? Jerry says 80% minimum on both lugs, 90% or better for NM type builds.

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Old March 19th, 2017, 06:39 PM   #3
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What are you shooting FOR? Jerry says 80% minimum on both lugs, 90% or better for NM type builds.
It just closes on a go gauge, with no slack. I am shooting for about 75%, like to get the H.S. in around 1.632 ish.

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Old March 19th, 2017, 07:05 PM   #4
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Getting closer to 70% and its still fits tight on the go gauge. Gonna take a little more off to get a little better contact.

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Old March 19th, 2017, 07:16 PM   #5
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Quote:
Originally Posted by mb3 View Post
Getting closer to 70% and its still fits tight on the go gauge. Gonna take a little more off to get a little better contact.
I would not try to head space the action by lapping. Looks like you have good contact on bolt lugs.

I would try a finish reamer, pull thru type, to set the head space.

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Old March 19th, 2017, 08:10 PM   #6
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The pics above show around 70% on both sides. No need to go any
more unless you're lapping for headspace. Clear scotch tape adds about 0.002" to your headspace gauge.

Tony.

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Old March 19th, 2017, 08:47 PM   #7
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Quote:
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The pics above show around 70% on both sides. No need to go any
more unless you're lapping for headspace. Clear scotch tape adds about 0.002" to your headspace gauge.

Tony.
This....^^^^^^

Scotch tape is a great tool for making "custom" headspace gauges. I use it all the time

Check headspace with a GO plus 1 piece of scotch tape which should put you at approx. 1.632"


And I've lapped bolts to make headspace numerous times. If you're shooting for lug contact and increased headspace; then you might as well lap till your wrist hurts.

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Old March 20th, 2017, 03:44 AM   #8
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Thank you for your help. I'll try the scotch tape and see if I can get the bolt to close on the go gauge. Right now it closes nicely on the go gauge with a little more contact, and just a touch of slack.

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Old March 20th, 2017, 06:32 AM   #9
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What effect does the % of lug contact have?
If the contact % is smallish, does it get changed by repeated firing due to peening?
Is there a 'strength' issue about the contact %?

I think the primary concern is to have the contact area provide proper bolt alignment, regardless of whether the % is the same on both lugs.

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Endwell NY USA

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Old March 20th, 2017, 06:43 AM   #10
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close enough for government work

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Old March 20th, 2017, 07:07 AM   #11
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Quote:
Originally Posted by JayKosta View Post
What effect does the % of lug contact have?
If the contact % is smallish, does it get changed by repeated firing due to peening?
Is there a 'strength' issue about the contact %?

I think the primary concern is to have the contact area provide proper bolt alignment, regardless of whether the % is the same on both lugs.

Jay Kosta
Endwell NY USA
Jay,
Obviously I am no expert, but I believe you are correct on all accounts.

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Old March 20th, 2017, 07:20 AM   #12
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I asked the question last year for collective input. I find IRON WORKER's comments very enlightening as well as other's comments.

Why do we lap bolts? Is it for safety, reliability or accuracy?

Tony.

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