Measuring Case Volume

[Popsbengo]

In the spirit of whiling away some lockdown time 😁😁-  I'm doing some case capacity measuring for comparison purposes and also for Quickload calculations.  What's the community thoughts?

The usual method suggested is to derive case volumetric capacity from water filled weight, less the dry weight (I should refer to 'mass' but weight will do).  The resultant weight of water derives the volume of the case and that's the important parameter for internal ballistics pressure calculations.

The received wisdom seems to be to use water in a trimmed and prepped, fire-sized case prior to full-length resizing:  Weight of H2O in grains is then entered into QL.  There's a few problems with that method:

1. water mass and volume vary with temperature:   By my calculations QL uses a normalised temp of 25C (77F) in their conversion (0.998 SG at 25C)
2. water out of the tap could be full of minerals and will have dissolved gasses therefore the weight is not just pure water
3. water produces a pronounced meniscus and entraps bubbles making it hard to be precise and introduces measuring errors
4. a fired case will have residues coated onto the inside of the case

Of course we can improve on this by using de-gassed, distilled water at room temperature in cleaned cases.  A tiny amount of rinse-aid will help with wetting so reduce bubbles and meniscus.

OR

don't use water at all.  In my past working life we needed to measure capacity but used clean filtered paraffin (kerosene to our American friends) at standard room temperature.  Paraffin does not form a noticeable meniscus and it doesn't entrap air and, as we derive its mass by weighing, the chemical constituents are allowed for.

1. Measure out, say 200ml of paraffin at room temperature and weigh it  (I pick 200ml as I have a lab cylinder that's ±1% and it's almost 60x the amount of a .308 so I get a decent sample size. Also that's about 164g so my scales are in range).   This is ensure you have an accurate SG reference as paraffins can vary
2. Use paraffin at room temp, fill the case and weigh as in the H2O method above
3. Using the volume/weight derived from (1) above calculate the volume of paraffin
4. use that volume in QL instead of "Grains H2O"

OK, some faffing about but no more than obtaining distilled, degassed water.  Advantages are no trapped bubble errors, no meniscus errors, no unknown SG errors.  Once the paraffin SG is determined just store in a sealed bottle for reuse as you need.

Thanks for reading, any thoughts?  

[srvet]

I think you have thought more about this than the rest of us!! 🤣🤣

Let us know the results, it would be interesting to compare H20 based volume with paraffin based volume

[Popsbengo]

2 minutes ago, srvet said:

I think you have thought more about this than the rest of us!! 🤣🤣

Let us know the results, it would be interesting to compare H20 based volume with paraffin based volume

Good idea!  I'll do that and tabulate the results

[BlueBoy69]

You don't mention anything about the primer. Are you plugging the pocket, using a fired primer, using an inert primer, or an unfired primer?

If you are going to this level of detail not accounting for the volume in the primer area would seem to be a bit neglectful.

At a guess, a fired primer would be best. This accounts for the loss in volume due to the firing pin indentation, and the increase in volume due to the combustion of the primer composition. Some of its combustion products are soilds, but I can't remember the exact ratio of soilds to gases.

[Popsbengo]

Fired primer in situ.  I figured like you, combustion takes place after the primer is deformed.  Off to do some comparison tests now

[miki]

I use a fired primer, which I inset, after the case has been wet tumbled, prior to FL resize. I set the scale to zero with empty the case, use (cold) boiled water, fill the cases with a syringe (whilst submerged in the jug) and then leave on a piece of kitchen towel for a while. On the scale I get the H20 volumetric weight.

I typically weigh/check 20 cases out of 100 (a batch) and average the results. My .25-06 PPU average @ 68.75 and the FC @ 67.65gr - thinner brass (or head) on the PPU I guess...

[38super]

This is interesting as a subject but I wonder if the capacity differences averaged out over perhaps 15 or

20 cases will make it academic only. Where do you draw the line. Do you only measure first fired cases ?

Twice or trice fired cases may have less internal volume due to powder residue. Perhaps better just to tweak QL mildly to

have your results in line with load real data and carry on.

I'll still be interested in the difference you see with paraffin.

[Re-Pete]

Paraffin SG varies..........the spec is from 0.78 to 0.82, so in a hair-splitting exercise like this, water might be more precise.

You might want to check this out: https://www.engineeringtoolbox.com/water-temperature-specific-gravity-d_1179.html

And this: https://www.engineeringtoolbox.com/specific-gravity-liquids-d_336.html

Don't forget to allow for the coefficient of expansion with temperature................😂

Pete

[Popsbengo]

5 minutes ago, Re-Pete said:

Paraffin SG varies..........the spec is from 0.78 to 0.82, so in a hair-splitting exercise like this, water might be more precise.

You might want to check this out: https://www.engineeringtoolbox.com/water-temperature-specific-gravity-d_1179.html

And this: https://www.engineeringtoolbox.com/specific-gravity-liquids-d_336.html

Don't forget to allow for the coefficient of expansion with temperature................😂

Pete

You're right Pete that's why I measure the paraffin and calculate the SG (point 1 in my use paraffin option list).  I'm aware of all the things you mention but thanks anyway 😁

 

[Popsbengo]

just in case you think I might be splitting hairs here!  Food for thought:

many of us claim to vary powder charge weight by 0.1gr steps and see results, well here's some interesting info derived from QL:

1. I've used .308Win, 24" barrel, N140, 155 Scenar as a base.
2. I keep the case volume constant and vary the powder charge ± 0.1gr  (Using QL standard for CIP case of 55.7gr H2O)
3. I keep the powder charge constant and vary the case volume by ±0.3gr water (using QL standards)

You will see that the resultant Mv are affected the same amounts.

How many of us measure water capacity to 0.3gr in 55gr ??   My sample of ten fully selected (but not by volume) and prepped Lapua cases vary by just a tad over ±0.3gr H2O

 

 

 

[miki]

3 hours ago, 38super said:

This is interesting as a subject but I wonder if the capacity differences averaged out over perhaps 15 or 20 cases will make it academic only. Where do you draw the line. Do you only measure first fired cases ?

Twice or trice fired cases may have less internal volume due to powder residue. Perhaps better just to tweak QL mildly to have your results in line with load real data and carry on.

I always wet tumble my cases so they are 'clean inside' when I measure. Over 20 cases the min/max was 1.2gr (H20) with PPU and 0.8gr with the FC (.25-06)

First or Second fired are very similar.

What difference does it make ? In GRT the difference is @ 68.8H20 I get 61508 psi and with 70.0H20 58981psi Max pressure is 63817psi so the smaller volume is closer to max. The MV also changes by approx 30fps, which i'm not worried about as i'm not shootong further than 250 to 300yds, nor am I shooting competitively (where is the spell checker when you need it ?) However I can see the need for perfection and hunt for constant pressure and MV that the long distance shooter desires.

[Popsbengo]

The results of my small batch tests are in:

10 Lapua .308; once fired cases, primer fired and in situ,  cases were fully prepped for length and selected for weight (of the case) prior to first firing.  Case volume is approximately 36.5cm3

1. The case volume, by H2O measured difference between tap water (straight out of the tap) and distilled de-gassed water is 0.05% - this is a trivial amount below the measuring limit of my equipment.
2. The paraffin gave a capacity value that was consistently 1.1% less capacity than the water derived capacity.  I surmise this may be due to the difference in meniscus between water and paraffin.
3. The SD between cases using the water method is 0.131 (distilled water at 16C)
4. The SD between cases using paraffin is 0.135 (paraffin SG measured not assumed)

Conclusion:

1. If you have reasonably neutral tap water, ie not high in mineral content, don't waste effort with distilled water
2. Water is more difficult to de-bubble when filling the case than paraffin but not by much
3. Due to surface tension I'm not convinced either fluid actually goes into the flash hole to fill the primer void so just plugging the flash hole is good enough
4. Paraffin isn't worth the effort, is a contaminant and cases need thorough cleaning afterwards
5. Pressure effects (Mv) from case volume are easily as important as accurate & precise measurement of powder if one desires 1/10th grain powder increment testing

That's been an interesting waste of my time, curiosity satisfied.  The most useful information I've gleaned is to batch cases on volume; it's not good enough to just weigh empty cases.  To anyone that reckons they can see 1/10th grain powder differences in Mv that doesn't batch cases by volume I suggest you may be fooling yourselves.

I need a bacon sandwich now

 

[KABOOM]

On 5/11/2020 at 8:16 AM, Popsbengo said:

In the spirit of whiling away some lockdown time 😁😁-  I'm doing some case capacity measuring for comparison purposes and also for Quickload calculations.  What's the community thoughts?

The usual method suggested is to derive case volumetric capacity from water filled weight, less the dry weight (I should refer to 'mass' but weight will do).  The resultant weight of water derives the volume of the case and that's the important parameter for internal ballistics pressure calculations.

The received wisdom seems to be to use water in a trimmed and prepped, fire-sized case prior to full-length resizing:  Weight of H2O in grains is then entered into QL.  There's a few problems with that method:

1. water mass and volume vary with temperature:   By my calculations QL uses a normalised temp of 25C (77F) in their conversion (0.998 SG at 25C)
2. water out of the tap could be full of minerals and will have dissolved gasses therefore the weight is not just pure water
3. water produces a pronounced meniscus and entraps bubbles making it hard to be precise and introduces measuring errors
4. a fired case will have residues coated onto the inside of the case

Of course we can improve on this by using de-gassed, distilled water at room temperature in cleaned cases.  A tiny amount of rinse-aid will help with wetting so reduce bubbles and meniscus.

OR

don't use water at all.  In my past working life we needed to measure capacity but used clean filtered paraffin (kerosene to our American friends) at standard room temperature.  Paraffin does not form a noticeable meniscus and it doesn't entrap air and, as we derive its mass by weighing, the chemical constituents are allowed for.

1. Measure out, say 200ml of paraffin at room temperature and weigh it  (I pick 200ml as I have a lab cylinder that's ±1% and it's almost 60x the amount of a .308 so I get a decent sample size. Also that's about 164g so my scales are in range).   This is ensure you have an accurate SG reference as paraffins can vary
2. Use paraffin at room temp, fill the case and weigh as in the H2O method above
3. Using the volume/weight derived from (1) above calculate the volume of paraffin
4. use that volume in QL instead of "Grains H2O"

OK, some faffing about but no more than obtaining distilled, degassed water.  Advantages are no trapped bubble errors, no meniscus errors, no unknown SG errors.  Once the paraffin SG is determined just store in a sealed bottle for reuse as you need.

Thanks for reading, any thoughts?  

Good sir that's 99% more thought than I ever thought possible on the subject, While I agree consistency is key, I limit my self to cases from the same lot and manufacture. I do find it interesting. Best wishes for good shooting.

[Popsbengo]

4 minutes ago, KABOOM said:

Good sir that's 99% more thought than I ever thought possible on the subject, While I agree consistency is key, I limit my self to cases from the same lot and manufacture. I do find it interesting. Best wishes for good shooting.

Thanks, I think CV19 has much to answer for 😁

[gruntus]

Hi Pops,

If it's of any help, I add alcohol (not the drinking kind, that would be a waste)  to the demin water as recommended by a fellow "time wasting, tail-chasing traveller". It helps with the miniscus. 

With regard to plugging the rear end (ooooh matron), a piece of blue-tac can be used (weighed to 2 x grains) as well.

Similarly with  bubbles how can you ever determine if the flash hole has air or water in it or a variance in between? 

How was the bacon sandwich?

ATB

G

 

[Popsbengo]

Gruntus,  I used a tiny amount of dishwasher rinse-aid as it's a powerful wetting agent - seems to work.  I keep all forms of alcohol for drinking only 😉

With regard to the flash hole bubble, I agree, it's not possible to know one way or the other hence just plug it - I like blu-tac as an option although I've seen a cleaver little fixture that you sit the case on and way the lot.

Bacon was a blow-out, had cold meatloaf butties instead - yum

[miki]

 

17 minutes ago, Popsbengo said:

Bacon was a blow-out, had cold meatloaf butties instead - yum

Ooh no, what a dissapointment. You can't beat a bacon sammy especially on some fresh home made bread (her in-doors is doing a stirling job in that dept these days) and a mug of piping hot, milky, tea. 

[Re-Pete]

Where are you getting the yeast and bread flour from??? We can't find yeast (quick kind for bread machine), or any decent wholemeal flour anywhere (or online).............

Pete

[Popsbengo]

42 minutes ago, Re-Pete said:

Where are you getting the yeast and bread flour from??? We can't find yeast (quick kind for bread machine), or any decent wholemeal flour anywhere (or online).............

Pete

I blame myself for introducing a bacon sandwich - If there was a prize for off-topic it's yours Pete!  😁

[Re-Pete]

No, Gruntus is more deserving........................

Pete

[gruntus]

37 minutes ago, Re-Pete said:

No, Gruntus is more deserving........................

Pete

😁 Guilty as charged.

[miki]

8 hours ago, Re-Pete said:

Where are you getting the yeast and bread flour from??? We can't find yeast (quick kind for bread machine), or any decent wholemeal flour anywhere (or online).............

Pete

Yeast from Lidl and strong flour from Costco (the last 18Kg bag) in Edinburgh.....  pm me your address and i'll send you a yeast 

[Triffid]

Back onto original subject . . .

I spent quite a few hours a couple of months ago trying to batch a load of 6.5cm cases by volume, because of exactly the issue Pops is talking about

Over 50 cases, I got a range of 52.0 to 52.9 gn water capacity.

However I decided to look at how repeatable my measurements were, weighing ten cases twice each. I found my measurements varied by up to 0.2 gn, which rendered the whole process rather pointless. I tried using some rinse-aid in the water to drop the meniscus effect, but that made little difference. Possibly my eyesight just isn't good enough to give the consistency I need!

So now the offending cases are still sitting on my desk. My next plan is to try a completely different liquid and I was thinking of meths. I'm not bothered by the exact figure it gives, just that it's repeatable. 

Triffid

[Re-Pete]

Triffid, I shine a torch across the top of the filled case and add drops of water using a hypodermic syringe with a fine needle..............it's easy to see if the meniscus is flat (required), concave , or convex from the reflection of the light from the water surface.

Thanks Miki, we'll give the local Lidl another go first.

Pete

[Popsbengo]

1 hour ago, Triffid said:

Back onto original subject . . .

I spent quite a few hours a couple of months ago trying to batch a load of 6.5cm cases by volume, because of exactly the issue Pops is talking about

Over 50 cases, I got a range of 52.0 to 52.9 gn water capacity.

However I decided to look at how repeatable my measurements were, weighing ten cases twice each. I found my measurements varied by up to 0.2 gn, which rendered the whole process rather pointless. I tried using some rinse-aid in the water to drop the meniscus effect, but that made little difference. Possibly my eyesight just isn't good enough to give the consistency I need!

So now the offending cases are still sitting on my desk. My next plan is to try a completely different liquid and I was thinking of meths. I'm not bothered by the exact figure it gives, just that it's repeatable. 

Triffid

I re-weighed my cases to test my methodology and I was satisfied that it was repeatable enough to be worthwhile.  It's a faff but I like the result.  I use a straight scalpel blade to scrape over the neck, it seems to give me a reasonably consistent meniscus.  Not needed with paraffin but I think I've put that out of my mind now.

I think I've proven to myself that it's worthwhile to batch cases by volume rather than dry weight of brass - even with Lapua cases there was more variability than I thought by dry weight alone.  

With regard to your 0.2gr:   In a .308 case this is equivalent to under 1/10gr of powder (N140).  Using your 52.0 - 52.9 that's about a 60fps difference for the same charge of powder (ball-park).  Worth avoiding that variance I feel even if it's not a perfect result.

Using my example I'm not convinced that a resultant  ±20 fps in 2,750 fps from the error of ±0.2gr in water weight volume is a big deal when stacked up against so many variabilities.  In larger cases like .338LM, the error is piddling

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 😁