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Measuring Case Volume


Popsbengo

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On 5/13/2020 at 11:39 PM, Popsbengo said:

Meths is a poor choice I feel - the evaporation will affect results.  I'm willing to be corrected and try it if you find it actually works well !

Of course:  we assume the bullet base is splendidly controlled and therefore when inserted into the case the resultant volume is still within a gnats nadger 😁

I have revisited my experiment since May, using some of the ideas above. I've now got the variation on re-weighing a single case down to a few milligrams - perhaps 0.05 grain - so well worth doing.

The technique I used is

1. Use Meths. It's great. No bubbles to contend with and the cases dry out quickly afterwards. I even give the case a good shake when its part filled to 'wet' the inside - this gives lots of bubble with water/detergent/rinse-aid, but none with meths.

2. Get the light right using a flexible task lamp.

3. Move the scales so the top of the case is at eye height.

4. Get a hypo-needle and syringe from ebay, This makes the amount of liquid you add very controllable compared to a plastic dropper pipette.

5. There's a 'sweet spot' when you're filling a case when the meniscus is completely flat. Trying to hit the same amount of curvature on the meniscus didn't work for me. You can only see the 'sweet spot' when the light is right and your eye is at the right level.

 

Sounds all complicated, but I weighed 120 cases in an hour. Just got to get to the range now to see whether it makes much difference in reality!

Triffid

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5 minutes ago, Triffid said:

I have revisited my experiment since May, using some of the ideas above. I've now got the variation on re-weighing a single case down to a few milligrams - perhaps 0.05 grain - so well worth doing.

The technique I used is

1. Use Meths. It's great. No bubbles to contend with and the cases dry out quickly afterwards. I even give the case a good shake when its part filled to 'wet' the inside - this gives lots of bubble with water/detergent/rinse-aid, but none with meths.

2. Get the light right using a flexible task lamp.

3. Move the scales so the top of the case is at eye height.

4. Get a hypo-needle and syringe from ebay, This makes the amount of liquid you add very controllable compared to a plastic dropper pipette.

5. There's a 'sweet spot' when you're filling a case when the meniscus is completely flat. Trying to hit the same amount of curvature on the meniscus didn't work for me. You can only see the 'sweet spot' when the light is right and your eye is at the right level.

 

Sounds all complicated, but I weighed 120 cases in an hour. Just got to get to the range now to see whether it makes much difference in reality!

Triffid

If it works, it works !

I find water to be ok - I've started testing with a seated bullet through the flash hole.  Got some 18g blunt nose hypo needles  -perfect

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Upturned case - seated bullet - primer removed 

weigh

 

fill with water through primer hole using syringe 

 

weigh again 

 

have upturned case supported in plasticine or similar

 

perfect and accurate case available space volume  

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Thanks Ronin, that looks like a great method of doing it to get an accurate case volume measurement, but given my experience with meths/water/rise-aid etc, I'd be concerned that there is entrapped air and/or bubbles within the case. How repeatable is that method? Have you tried it measuring case volume at different bullet seating depths to 'calibrate' the volume against seating depth with that particular bullet?

However I'm doing this to batch my cases according to volume, and the exact figure isn't important. So the upturned case method is not really suitable.

Triffid

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I used it for two cartridges that I load 

one was an established load using 550, the other a load I was developing 

I found it repeatable if you inserted the blunt needle into the primer flash hole with no air in the syringe and (important) fill the case to overfill allowing spillage which encourages air bubbles to vent out the primer flash hole

once clear water was flowing I drew back a tiny amount to the base of the primer pocket 

wipe over with paper towel and weigh on scale 

 

pretty repeatable to less than a grain in my “cases” and I then used an average for final calculation / entry into P-max

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