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Checking bolt lug contact

This is a discussion on Checking bolt lug contact within the Gunsmithing forums, part of the M14 M1A Forum category; Got my rifle back from SAI sometime ago and haven't shot it since. I figured checking the lug contact would be something good to do ...


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Old September 10th, 2013, 04:01 PM   #1
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Checking bolt lug contact

Got my rifle back from SAI sometime ago and haven't shot it since. I figured checking the lug contact would be something good to do even though I didn't check the original bolt either. Am I supposed to use permanent marker or dry erase? All the posts here talk about magic markers and was wondering which type of marker is used. Thanks guys.

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Old September 10th, 2013, 04:55 PM   #2
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Sharpie on the back of the lug. Make sure you remove all the grease first.


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Old September 10th, 2013, 05:07 PM   #3
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Gotcha. Permanent marker it is. I used permanent marker on the rear of the bolt lugs and hand cycled it with the stripped bolt and a punch but without a cut casing and spring. There seems to be very little contact on the rear bolt lugs. Is the cut casing and spring necessary?

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Old September 10th, 2013, 06:08 PM   #4
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Quote:
On a new bolt, the way to check fit is to clean and dry the lugs in both bolt and receiver, and use a permanent felt pen [ RED is nice ] to mark the bolt lugs. With slight rearward tension, work the bolt up and down a few dozen times, remove the bolt, and inspect the wear pattern scraped out of the red ink. What you are looking for is EVEN wear on the locking lugs, with MAXIMUM bearing on BOTH lugs
From Laz

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Old September 10th, 2013, 06:12 PM   #5
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Red sharpie permanent.
Flush and clean with alcohol and Q tips first.

PS: I checked over a NEW Springfield M1A Standard that had been returned for a GI bolt install because the owner did not want the Spinger cast bolt. Fresh back from the SAI service center, still un-fired, the GI bolt did give good head space, but the lug contact was not optimal. A few minutes of lapping was all it took to fit up nicely.

While we often refer to a GI bolt swap as a "drop in", spending a few minutes checking for proper bearing on BOTH sides, and/or lapping the lugs in for maximum bearing are often required. NOTE I said a FEW minutes of lapping ... you are not treying to adjust head space here, merely optimise lug to lug bearing.
[;)
LAZ 1

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Old September 10th, 2013, 11:26 PM   #6
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thanks for the tips guys. I'll try to do this tonight and report back with what I find.

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Old September 11th, 2013, 03:20 AM   #7
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You may have to zoom in on the pictures to see where the red permanent marker was rubbed off. To me it seems like the right bolt lug is receiving about70% contact and the left lug is receiving 35-40%. I honestly wasn't expecting this much contact with a bolt replacement from SAI. Should I lap both lugs so that the left lug manages more contact? Thanks again!




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Old September 11th, 2013, 04:22 AM   #8
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That's excellent contact, i wouldn't worry about lapping it

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Old September 11th, 2013, 01:49 PM   #9
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Great to hear/read! Thanks again!

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