Measuring water capacity--how?

[condor bravo]

After filling a number of cases with water up to the neck, what is the procedure for measuring or weighing the water for comparisons? Like pour the water from each case into your scale pan and weigh them??

[RC20]

Whatever works.

Weight the case first, then weight it with water in it.

Me, if I want to know I weight it and fill it with ball powder.

Close enough and that tells me what the real difference is.

Water is far denser than power by 3.5 to 1.

[Reloadron]

Read this thread it gets pretty well covered. Yes, you weigh a case, fill the case and weigh it again. Then simply subtract the difference subtracting empty weight from full weight. You may want to note the prep done before even weighing the cases, especially if comparing different manufacturers or head stamps.

Ron

[higgite]

RC20 and Ron are right. Weigh the dry, empty case first, then fill with water and weigh again. You won't get accurate results if you fill the case and then dump the water into your scale pan and weigh it. The case will be heavier after dumping the water than it was when dry, meaning some water is left behind in the case. Some clings to the case wall and I suspect some is soaked up by the spent primer.

FWIW, I zero the scale with the dry case then weigh the filled case. Saves doing the math.

[Reloadron]

FWIW, I zero the scale with the dry case then weigh the filled case. Saves doing the math.

That thought never crossed my mind and should be so obvious. Well duh on that note.

Ron

[condor bravo]

I'm sort of thinking that with the case full of water, it might be difficult to balance on a free swinging scale pan and possibly tip over. By pouring just the water into the pan, about the same amount of water should remain in each case after pouring, thereby evening the net weights out accordingly.

[hounddawg]

I'm sort of thinking that with the case full of water, it might be difficult to balance on a free swinging scale pan and possibly tip over.

probably right about that, if you want to use a beam scale then take RC20's advice and use a fine ball or flake powder. I never thought of that myself but if I decide to do case volume again that is what I will do. It will be a whole lot easier and less of a mess. Faster too since you won't have to bother with case weight or any math

EDIT - I was bored and tried the powder method using TAC, a new 260 case ( primed) and both my RCBS CM scale and my beam. I used a 4cc powder dipper, a funnel with a 4 inch drop tube with a case sitting in a plastic tub to catch excess powder. I filled the case with powder, removed the funnel, poured the powder into a pan and weighed it. I repeated this ten times with the same case and had a extreme spread of over a grain and a half. I then did it again this time gently tapping the case ten times to pack the powder before removing the funnel and doing the weighing. It was a little better but still way too high of a extreme spread for this method to be useful.

Sorry RC20 it sure sounded good on paper. I may try again and this time rotate the case a few times with my finger over the neck and a "topping off " of powder. I suspect the shoulder area was not filling evenly

[RC20]

Ok, real life test.

I took 50 cases of Lapua 308. The largest disparity was 5 grains (extreme, most were closer to 2 grains )

I then over filled the lightest case full of 748, then scraped off the excess and weighed it.

I repeated that with the heavier case.

The light case held more powder, the heavier case less.

The difference was 7/10 of a grain.

That is +/- 3.5 tenths off the average.

That assume the neck does not affect the issue.

[hounddawg]

can you take the same case and fill it 10 times and get the same weight plus or minus a tenth for scale error? I could not with TAC flake but will repeat using Win 748 which is a fine ball tonight. I want the powder trick to that to work but could not figure out why I could not get repeatability. I am experienced over a grain of difference at times on the same case.

As I said in my post last eve I suspect filling to the mouth covering it while inverting and then topping off might do the trick

[Yosemite Steve]

I think that anyone who is going to make it a regular practice to weigh cases and volumes would be wise to invest in a digital scale. Waaaaaayyyyyyy faster.

[Reloadron]

I did a similar experiment last year but rather than a case I used a Lee Dipper, actually a Lee 2.8 cc Dipper. The powder I used was Hodgdon H-335. I loaded the dipper two ways. I left it un skimmed or un leveled and also skimmed it or leveled it using a straight edge.

Using a VMD (Volume Measure Density) chart from Lee the VMD of H-335 powder is 0.0645. Now it follows that:

CC setting (powder measure setting)
--------------------------------------- = VMD (volume in cc's for 1 grain)
Weight of the sample

2.8 cc (Volume / 0.0645 = 43.41 grains of powder.

I used a few known check weights and the scale was accurate and repeatable. Here were the results I got.



The target weight again was 43.41 grains. All of the charges were over with an average of 44.7 grains on the skimmed dipper loads.

As to the VMD of powders? I am not sure as one of my reads on the subject claims:

It is very important that you repeat this process with any new container of the same powder because the powder companies allow themselves a 16% tolerance between batches. This can result in over charging if you work from the same setting and the next container of powder you get is more dense.

Maybe later today I'll do a similar test but use a cartridge of known capacity and use a stick powder like IMR 4895 or AA 2495.

Ron

[hdwhit]

As noted, the easiest and most straight-forward way to do it is to weigh the case dry, fill it with water and weigh it again. If using a beam balance, you can hold the "basket" with one hand to stop it moving around while you put the filled case in it.

Or you could invest in an inexpensive digital scale (around $20).

Or you could invest in some graduated labware so that you measure the amount of water you put in the syringe, burette, pipette, etc., fill the case and then see how much water is left in the device you used to dispense the water.

[hounddawg]

just made another try at the powder method using the Win 748 and discovered the secret to substituting powder for water is no tapping or packing. The best method I found was to set the case in the saucer and make sure the dipper was full and level then drop through a funnel into the case. The funnel was then lifted carefully to allow any excess powder to fall into the saucer with as little disturbance as possible to the case then leveling the top of the case with my knife.

I was able to keep within plus or minus .1 grains which is the limit of accuracy on most electronics. I never tried it on the beam but that could show that it is even more accurate. The 748 was about the same consistency as the TAC and tapping or packing it would give an error of up up 1.5 grains

So my conclusion is yes weighing using the powder method is doable but care must be taken when filling. I doubt if I will bother with weighing however. I am getting very consistent velocities with low ES and SD without doing so