Pneumatic case volume measure - Page 2

polyphemus · January 10, 2016, 11:04 AM

Boyle's Law.

**Unclenick** · January 10, 2016, 11:09 AM

Adidas69,

I found the Extech 750 has the range and resolution you want and is $220, here. If you wait for a sale, it will go down.

Note that your Ashcroft gauge, though it resolves 0.001 psi, has an accuracy of 0.5% of full scale, which, at 45 psi full scale, is 0.225 psi, though you can buy one with twice that precision. The Extech is 0.3% of full scale, which, for the 5 psi unit would be 0.015 psi, but you can't go over 10 psi without damaging it. It is a differential meter, so your psi would be above the outside air pressure, which may be what you want.

If this is something you are thinking of selling to handloaders, then I believe you are looking at putting your own gauge together. I looked at transducers and found one for $40 that beat the Extech specs with ±0.25% accuracy at Digi-Key, but the minimum order was 20 units.

hartcreek · January 10, 2016, 11:10 AM

Good grief........why would anyone waste so much money when all you need to do is segregate by case head stamp and weigh a few to determine the heaviest cases and then actually use primed cases to measure the difference in maximum charge weights for the different head stamps.

500 good grief I have done it with lots of 1000 of mixed head stamp brass you are just making this much harder then it needs to be as all you have to do is establish the head stamps that have the least capacity and use that load for all the head stamps.

I did this with .308 and 30-06 and the variance was 5 grains with H414 which is what I primarily use now.

**Unclenick** · January 10, 2016, 11:45 AM

You also often have to sort it by lot. Here's a link whose data includes two lots of Winchester 243 cases, both with 54.8 grains average case water overflow capacity and one lot with an average weight of 158.58 grains and the other with an average weight of 166.44 grains, despite that identical internal capacity. I, too, have noticed Winchester's weight going up since they moved the plant from Alton, Illinois. I don't know if it's because they changed tooling, or if it's because they are outsourcing some of it and the tooling style used by the new supplier is different.

The thing to bear in mind is that the thickness and diameter of the head, the rim and the extractor groove depth and relief angles all have tolerances that affect the case weight, but not the interior volume. So tooling changes can affect results.

Wm. C. Davis showed a long time ago that for most rifle cartridges, when the heads were identical, you had to have about 16 grains of case weight difference to need one grain difference in powder charge. I've found some powders for which it's more like 14 grains, so I use that as a worst case number. Both numbers assume cases made of 70:30 cartridge brass, which they all are not, complicating things a little with their alloy density differences.

Worst case, if you have a good load that can tolerate at least half a grain of charge variation without running off its sweet spot, you are looking at ±3.5 grains of weight variation either side of the case weight it was developed in before you risk sending it off the end of the sweet spot range. If there are other factors, like changing temperatures or sloppy charge dispensing that you need to have that insensitivity range as a buffer for, then you might want to hold your case weights a little tighter. But sorting them to tighter than a grain and a half of case weight or about 0.2 grains of water capacity is not worth spending much time on, as a 0.1 grains of powder is all the equivalent difference it will make.

Incidentally, in .30-06, 0.2 grains of water capacity is about 0.3% of total case volume. So that's the level of precision you want from a volume measuring method for that cartridge. Water is the easiest way to get it, as long as you keep in mind that water density varies with temperature and allow for it when you need to. When water is just about hot enough to boil at sea level, it expands almost 4.2%, which is the water density the volume of a fluid ounce is based on.

I expect the reason the OP wants the resolution he does is to be able to see differences that small between two cases quickly, even if the absolute number isn't true.

jaguarxk120 · January 10, 2016, 12:03 PM

A big cost is the regulators used to control air pressure. They are very special and very accurate.

Air Gage is used by many manufacture's to measure hole in part's and use's those regulator's along with electronics to measure the changes in air pressure.

F. Guffey · January 10, 2016, 12:11 PM

I have micrometers I put away what seems like many years ago. Some would call the gages snap gages, one set has three contacts. It would seem if the case volume is going to be measured it would be necessary to measure the case from the inside. I have gages that will do that, again, I have no interest/ambition to go through the trouble because I would have to modify the gages. It would be like doing a 100+ year upgrade.

Then there is measuring the thickness of the brass and the length of the powder column.

F. Guffey

I had a Pratt & Whitney electronic gage that measured down to .000005", not a useful tool when reloading. I removed the electronics then installed a dial indicator on the stylist. And now it is a height gage with 11' clearance.

higgite · January 10, 2016, 12:11 PM

Quote:

Good grief........why would anyone waste so much money when all you need to do is segregate by case head stamp and weigh a few to determine the heaviest cases and then actually use primed cases to measure the difference in maximum charge weights for the different head stamps.

Because he wants to? I'm pretty sure he said that somewhere in this thread.

polyphemus · January 10, 2016, 02:04 PM

Quote:

I had a Pratt & Whitney electronic gage that measured down to .000005"

Geez F. We had a P&W supermic.Model B at work but that unit resolved only to
.00005" You had some kind of highly accurate instrument there,and you took it apart because because it was of no use for ammo reloading purposes?
Those go for a lot of money you could have sold it an bought yourself a trinket or two.

F. Guffey · January 11, 2016, 11:52 AM

Quote:

Geez F. We had a P&W supermic.Model B at work but that unit resolved only to
.00005"

Polyphemus, I am not the politically correct one. I have no fewer than 6 dial indicators, by changing the gage from electrical to direct reading I did not loose much and then it would be most difficult to find a stand/comparator that operates smoother than the Pratt & Whitney.

Trinkets, The wife has put a stop to all of that, from now on nothing can be added unless it is small and no larger than a diamond.

F. Guffey

January 10, 2016, 11:09 AM	#27
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	Adidas69, I found the Extech 750 has the range and resolution you want and is $220, here. If you wait for a sale, it will go down. Note that your Ashcroft gauge, though it resolves 0.001 psi, has an accuracy of 0.5% of full scale, which, at 45 psi full scale, is 0.225 psi, though you can buy one with twice that precision. The Extech is 0.3% of full scale, which, for the 5 psi unit would be 0.015 psi, but you can't go over 10 psi without damaging it. It is a differential meter, so your psi would be above the outside air pressure, which may be what you want. If this is something you are thinking of selling to handloaders, then I believe you are looking at putting your own gauge together. I looked at transducers and found one for $40 that beat the Extech specs with ±0.25% accuracy at Digi-Key, but the minimum order was 20 units. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

January 10, 2016, 11:45 AM	#29
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	You also often have to sort it by lot. Here's a link whose data includes two lots of Winchester 243 cases, both with 54.8 grains average case water overflow capacity and one lot with an average weight of 158.58 grains and the other with an average weight of 166.44 grains, despite that identical internal capacity. I, too, have noticed Winchester's weight going up since they moved the plant from Alton, Illinois. I don't know if it's because they changed tooling, or if it's because they are outsourcing some of it and the tooling style used by the new supplier is different. The thing to bear in mind is that the thickness and diameter of the head, the rim and the extractor groove depth and relief angles all have tolerances that affect the case weight, but not the interior volume. So tooling changes can affect results. Wm. C. Davis showed a long time ago that for most rifle cartridges, when the heads were identical, you had to have about 16 grains of case weight difference to need one grain difference in powder charge. I've found some powders for which it's more like 14 grains, so I use that as a worst case number. Both numbers assume cases made of 70:30 cartridge brass, which they all are not, complicating things a little with their alloy density differences. Worst case, if you have a good load that can tolerate at least half a grain of charge variation without running off its sweet spot, you are looking at ±3.5 grains of weight variation either side of the case weight it was developed in before you risk sending it off the end of the sweet spot range. If there are other factors, like changing temperatures or sloppy charge dispensing that you need to have that insensitivity range as a buffer for, then you might want to hold your case weights a little tighter. But sorting them to tighter than a grain and a half of case weight or about 0.2 grains of water capacity is not worth spending much time on, as a 0.1 grains of powder is all the equivalent difference it will make. Incidentally, in .30-06, 0.2 grains of water capacity is about 0.3% of total case volume. So that's the level of precision you want from a volume measuring method for that cartridge. Water is the easiest way to get it, as long as you keep in mind that water density varies with temperature and allow for it when you need to. When water is just about hot enough to boil at sea level, it expands almost 4.2%, which is the water density the volume of a fluid ounce is based on. I expect the reason the OP wants the resolution he does is to be able to see differences that small between two cases quickly, even if the absolute number isn't true. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

January 10, 2016, 11:04 AM	#26
polyphemus Senior Member Join Date: June 24, 2012 Posts: 1,055	Boyle's Law.

January 10, 2016, 11:10 AM	#28
hartcreek Junior member Join Date: April 22, 2014 Location: Washington Posts: 1,549	Good grief........why would anyone waste so much money when all you need to do is segregate by case head stamp and weigh a few to determine the heaviest cases and then actually use primed cases to measure the difference in maximum charge weights for the different head stamps. 500 good grief I have done it with lots of 1000 of mixed head stamp brass you are just making this much harder then it needs to be as all you have to do is establish the head stamps that have the least capacity and use that load for all the head stamps. I did this with .308 and 30-06 and the variance was 5 grains with H414 which is what I primarily use now.

January 10, 2016, 12:03 PM	#30
jaguarxk120 Senior Member Join Date: February 28, 2008 Location: Michigan Posts: 2,619	A big cost is the regulators used to control air pressure. They are very special and very accurate. Air Gage is used by many manufacture's to measure hole in part's and use's those regulator's along with electronics to measure the changes in air pressure.

January 10, 2016, 12:11 PM	#31
F. Guffey Senior Member Join Date: July 18, 2008 Posts: 7,249	I have micrometers I put away what seems like many years ago. Some would call the gages snap gages, one set has three contacts. It would seem if the case volume is going to be measured it would be necessary to measure the case from the inside. I have gages that will do that, again, I have no interest/ambition to go through the trouble because I would have to modify the gages. It would be like doing a 100+ year upgrade. Then there is measuring the thickness of the brass and the length of the powder column. F. Guffey I had a Pratt & Whitney electronic gage that measured down to .000005", not a useful tool when reloading. I removed the electronics then installed a dial indicator on the stylist. And now it is a height gage with 11' clearance.