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Discussion Starter #1


Finished lapping the bolt on my first M14 build. Wanted to stop around 75% contact on both sides. Left lug needed a little more work than the right.

How did I do?



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Pending response from an actual expert, I'd say it looks like you got enough contact.

The only useful thing I can contribute, which does you no good now if you don't already know, is passing on the technique parameter of keeping the lapping motion 'low' on the receiver (nearer closed) as reasonably possible, so you're not grinding on the corners of the lugs. That way, you're not just removing finish on the surfaces, you're increasing surface contact when the bolt is actually closed.

Is this actually critical? Different experts have different answers. I'd prefer to maximize contact, just because, though at least a couple guys who turn out great-performing rifles don't even bother lapping the bolts.

Looking forward to hearing thoughts of those who have experimented with different methods.
 

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Discussion Starter #3
That I did. Kept the strokes very short. I’m mostly following the Kuleck & McKee assembly guide, but did watch Tony Ben’s YouTube video on barrel installation and he mentioned that.


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The amount of contact is less important than having an equal amount of contact on each lug.

The point of this exercise in to insure that the bolt is supported equally on both sides and square to the bore axis.

And one last thing, try and maintain the helix of the locking surfaces and don't get carried away and chew through the carburized shell.
 

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what grit lapping compounds do you guys prefer or suggest? I have some to do soon and need to buy some. Brand, type, grits will be helpful.

your work looks great to me. Do you plan to cold blue those lapped areas now?
 

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I’ve thought about cold-bluing the lugs, but wonder if it would just wear off under use.

I used the 240 grit abrasive compound from Brownell’s. Bought the smallest container, but it’s vast compared to the tiny amount I actually used.


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Cold blue is a good idea. It will wear off in use, showing you the actual contact pattern after the rifle has been fired.
Blue the lugs, fire off a hundred rounds and show us what the wear pattern looks like.
 

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I used suggestions from Art (nf1e). I use a black sharpie and coat the backs of the lugs, install bolt and use a hammer spring inserted in a cut .308 casing for back pressure on barreled actions, or a lapping tool set (Brownells) for bare receivers. Rock the bolt several times and see how much ink was removed. If it looks like I have to take a lot off I start with valve grinding compound (Permatex). If it doesn't need a lot I start with 600 grit lapping compound until I see good contact. Then move on to 800 grit lapping compound for a nice smooth "mirror" finish.
 
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