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How do you measure crimp?

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How do you measure crimp? - Page 2 Empty How do you measure crimp?

Post by Merick 11/17/2021, 2:07 pm

First topic message reminder :

This is kind of a spin off of the load optimization thread, but I never felt all that confident in measuring crimp. 

Round micrometer anvils rolling over the end of a tapered/rolled case mouth just feels problematic, calipers even worse. 

To far down the case and that isn't a true reading, too far out and square anvils roll off the edge.

*I'd think one of those hornady oal anvil sets with one insert reamed on a taper would give consistent results, and you'd have to do some math of case length vs taper length reading to get a real crimp diameter number, and you'd need a gauge to set it against to have numbers you could swap with anyone else.  Maybe that is way off base.

What is the correct way to measure the end diameter of a cone?

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Post by CR10X 11/19/2021, 10:20 am

Look at it this way.

Too little crimp is not good.

Too much crimp is not good.

Just a little less than too much is usually just right.

You just need to find the boundaries and then get somewhere in between. 

Then if you dryfire a lot the groups will probably tighten up a little more.

CR

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Post by WesG 11/19/2021, 10:23 am

Nothing wrong with dial calipers, until you get a chip in the rack and it skips a tooth. But that assumes it's  a quality piece to begin with, not one of the plastic toys.

The point of a micrometer being better, I think, is that it presents a rounded edge to eyeball across. Easier to see, and a lot easier to manipulate than a caliper, which you'd have to use the tips of for the same effect.

Ultimately, it's only a reference for a starting point, and a fall back during testing. A wild guess by eyeball, and a sharpie mark on the lock ring so you have something to make note of during testing, is probably as good as measuring.

Similarly, the gauge Wes L has doesn't need to measure an absolute value, just provide a repeatable reading that's close enough to the crimp you're trying to achieve as a baseline.

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Post by RodJ 11/19/2021, 12:44 pm

All this crimping, debelling, case straightening to a specific measurement using a tapered die is a mess if you’re not sorting cases by length or god help you, trimming. And I’m not really up for either exercise. Longer cases will be “crimped” / flattened / de-belled whatever more than shorter cases.  And then sorting by length still leaves you with different headstamps which means different brass thickness which means more or less brass pressed into the bullet. And then there’s still different lots of ammo…

Hence, the “coefficient of frickosity” - K(fr) - will vary greatly. And if you worry too much about these things you’ll never get anything done.

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Post by james r chapman 11/19/2021, 1:06 pm

Must be a BR shooter, eh?
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Post by RodJ 11/19/2021, 1:24 pm

james r chapman wrote:Must be a BR shooter, eh?

Yep. For about 45 minutes back in the early ‘90s (1990s) with a Lee Loader and 10 once fired 7mm mag cases at the breakfast table.  That included reading the instructions twice.  I think it was can of h4350 and a COMPLETE set of yellow spoons and the cardboard chart.  You shoulda seen me.  Los Alamos National Labs had nuthin on me.

Edit to add: and YES, same lot of brass and ALL Winchester primers.  Wanna buy a partial pack of 90 LR magnum primers?

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Post by zanemoseley 11/19/2021, 2:27 pm

RodJ wrote:All this crimping, debelling, case straightening to a specific measurement using a tapered die is a mess if you’re not sorting cases by length or god help you, trimming. And I’m not really up for either exercise. Longer cases will be “crimped” / flattened / de-belled whatever more than shorter cases.  And then sorting by length still leaves you with different headstamps which means different brass thickness which means more or less brass pressed into the bullet. And then there’s still different lots of ammo…

Hence, the “coefficient of frickosity” - K(fr) - will vary greatly. And if you worry too much about these things you’ll never get anything done.

If you're that OCD then you really need to be just buying cases of new Starline brass and keeping them in a batch. No shooter in their right mind will be trimming 45acp brass.

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Post by straybrit 11/19/2021, 2:31 pm

> No shooter in their right mind 

That's a contradiction of terms right there.

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Post by RodJ 11/19/2021, 3:18 pm

zanemoseley wrote:
RodJ wrote:All this crimping, debelling, case straightening to a specific measurement using a tapered die is a mess if you’re not sorting cases by length or god help you, trimming. And I’m not really up for either exercise. Longer cases will be “crimped” / flattened / de-belled whatever more than shorter cases.  And then sorting by length still leaves you with different headstamps which means different brass thickness which means more or less brass pressed into the bullet. And then there’s still different lots of ammo…

Hence, the “coefficient of frickosity” - K(fr) - will vary greatly. And if you worry too much about these things you’ll never get anything done.

If you're that OCD then you really need to be just buying cases of new Starline brass and keeping them in a batch. No shooter in their right mind will be trimming 45acp brass.

Hopefully no one reading this is thinking that I’m advocating all this OCD stuff.  The most I do is try to keep cases in groups by number of times fired, and cull weird headstamps.  Also, I found a bag of starline new brass squirreled away in my boxes.  I went OCD with 100 rounds and I don’t shoot well enough to tell any difference.  Maybe some day…

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Post by james r chapman 11/19/2021, 6:14 pm

Since the majority of points are with lubed rocks at 25 yd, I just use established loads suggested by the Master and HM shooters on this forum.

As far as 50 yd, at those same suggestions I use 185 jhp using new brass over suggested established loads.

As a 72 yr old I’m doing this for the challenge and the occasional 92-95 longline score tells me to not overthink the reloading process.
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Post by farmboy 11/21/2021, 6:36 am

I turn the case gauge upside down and rest the completed round on the case mouth over the hole. Lay the calipers on the case gauge as a rest and guide.
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