Micing Slug From Rifle Barrel
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Thread: Micing Slug From Rifle Barrel

1. Plastic
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Micing Slug From Rifle Barrel

Can anyone tell if if you can measure a slug you drove through a rifle barrel that has three groove rifling with a standard mic that has flat anvils? I'm not sure what the land to groove ratio is, but I know the groove is larger. If you need more data please ask. Thanks

2. Plastic
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Originally Posted by starmetal
Can anyone tell if if you can measure a slug you drove through a rifle barrel that has three groove rifling with a standard mic that has flat anvils? I'm not sure what the land to groove ratio is, but I know the groove is larger. If you need more data please ask. Thanks
Wrap it with a brass strip and mic the outside. Subtract 2x the thickness and you have it.

3. Hot Rolled
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get a different mic would be the most logical solution the one with the vee anvil it locates on 3 points. two on the anvil and one on the spindle.

4. Aluminum
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Originally Posted by Jpg366
Wrap it with a brass strip and mic the outside. Subtract 2x the thickness and you have it.
Not accurate enough for the purpose.

You can make a v block and do math.

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5. Plastic
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Originally Posted by pat_j0nes
Not accurate enough for the purpose.

You can make a v block and do math.

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I'm sorry I believe I asked the question wrong. We got a fellow on a forum that says you can measure a slug from a 3 groove barrel accurately with a standard 0 to 1 flat anvil micrometer. We're saying that he can't. We know about a V block mic. That's what I want to know is if it can be measured accurately with the standard mic. Thanks

6. Titanium
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In theory you could, assuming the spindle and anvil are the same diameter and concentric, by placing the edges of the spindle and anvil against the sides of the lands diameter (the smaller dia) for the land diameter, and centered on the edges of the groove diameter for the grooves diameter. This would require mechanical holding of the bullet for any chance of being accurate because one doesn't have enough hands otherwise.

Otherwise make a 120° included angle V block with an accurately positioned bottom flat and use that as the holding/measuring aid.
Last edited by GGaskill; 08-11-2019 at 06:04 PM.

7. Titanium
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I do have a Vee mike for checking centerless grinding out of round, most people do not.
I did check a 5 land barrel by measuring the bore with a pin gauge and got .301", using a ID mike from land to groove got .306". That told me the grooves that told me the grooves were .005 deep. Added double the .005 to .301 and got a barrel diameter of .311".
For the OP he could bore a piece of scrap to smaller than expected diameter and start enlarging it .001 at a time till it fits. That is assuming he has pin gauges or a ID mike to accurate check the ID.

8. Diamond
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The answer is NO!

Not directly, not accurately

Tri-lobal error is the bugaboo of diametric measurement.
saying otherwise is bleating in the dark

9. depends how wide the grooves are how sharp transition from land. With three grooves, there are places where you can bisect the slug without hitting the protruding grooves with one flat anvil hooking the edge next to extruded groove. This is assuming that slug's bottom is perfectly flat and you can position it so that its axis is perpendicular to the mic's plane.

I guess the real question is not about can it be done, but what's the procedure to maximize precision and what practical precision can be achieved here.

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