H2O case volume to powder charge amount question

M

Metal god

New member
I just started measuring actual case volume with water . I measure using fire formed cases from specific rifles . I have two questions .

1) If cases regardless of maker measure the same volume . Can they be loaded with the same charges ? Lets assume these are MAX loads for the question .

2) Is there a direct correlation from water volume to powder charge assuming you have a charge you know works well in a specific case . Let's say I have a 308 load I've used in X brass that has a water volume of 55gr . I want to load that same load in a different brand case but it's water volume is 48gr or 59gr ( just making up numbers here ) Is there a direct relation you can/should increase/reduce the charge based on the new internal volume case ?

Feel free to add to the conversation if need be like at what point less or more internal volume starts to make a difference in powder charge .
 
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Taking short cuts with reloading can lead to unexpected results.
The best approach is, and always has been, is to work up loads from scratch with every change in components.
 
Well I guess you can say I'm looking for a short cut . I don't look at it that way . I change cases all the time and reduce the charge and work back up . The key word there is reduce . I don't go back to minimum I usually drop the charge 1 to 1.5gr and work back up but not the 4gr back to minimum . Is that a short cut ? I'd have to say yes . Is it an unsafe way to go about it ? I don't feel it is .

The question comes from QL ( quick loads ) and how case volume is a critical part of it's evaluation of the charges . I don't run QL but have had other run my numbers through the program and is why I started doing the water test .

I can't say the answers I get here won't influence how I evaluate changing cases but this is really more of an information question . I just like to know as much as possible about reloading .

I remember when I first started and being told to weigh my cases . A change in weight meant a change in charge . Only to find out case weight has nothing to do with case volume . This is just another step in understanding this whole concept .
 
If this theory of measuring relative powder charges is correct, it's easy enough to verify.
Load the alternative size cases as expected, and check them at the range.
It will become readily apparent if the theory is correct or not.
If so, carry on.
If not, like most inventions and discoveries, it's back to the drawing board.
Either way, you will know for sure without conjecture.
Let us know of the results, please.
 
Don't over think the reloading process. It's not that complicated.
Unless you're shooting bench rest, water volume doesn't matter a whole lot. Not at all for hunting loads.
1) The brand makes no difference.
2) Smokeless powder isn't loaded by volume, but the volume of a case doesn't change the amount of powder use for whatever load you developed requires. For example, 7.62NATO is a standard for bullet weight and velocity. Who made the case doesn't matter.
 
Interesting you say that . I've read that old 308 cases can weigh about 155gr and modern ones Weigh 175 to 185 . I know I said weight does not matter but a 30gr difference will actually show an inturnal volume difference that charge weight should be adjusted for .

I am curious what others think about cases are cases , they're all the same . I've never heard that before . I separate all my rifle cases by head stamp and pistol case by head stamp or case wall thickness .

Am I to assume you are saying no need to separate your brass by head stamp .

FWIW I'm loading for target shooting from 100 to 900 yards
 
If your charge is near max in a case with an internal volume of say 55 grains, and you then drop your charge only 1-1.5 grains in a case that has an internal volume of only 50 grains, then you have a good chance of being grossly over pressure. In a case that has less volume, I would always drop back 10% and work back up.
 
Metal god wrote:
I just started measuring actual case volume with water. .....
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OK. Lets start with the basics:
1) How are you measuring case volume?
2) Give us the actual situation, not hypothetical please.
 
Prior responders have interpreted your query as signifying an intent to devise a load by determining case volume and urged caution. If that interpretation is correct, I join the caution urgers.

That said, the answer to your question, I believe, is this:

Convert H2O weight to H2O volume. (I believe at 70°F, pure water has a density of
8.329 lb./gal. Or 62.31 lb./cu.ft.)

Look up powder density of powder of interest.

After converting to common units, multiply volume by density.
 
Is this before or after you resize the case?
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Well lets start by quoting my self and the very first two lines of this thread

Me said:
I just started measuring actual case volume with water . I measure using fire formed cases from specific rifles
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OK. Lets start with the basics:
1) How are you measuring case volume?
2) Give us the actual situation, not hypothetical please.
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1) First I check to be sure all case samples are trimmed to the same length
2) I weigh a empty fire formed case .
3) Fill that same case with water and weigh it
4) subtract the empty case weight from the filled case weight to get my H20 case volume
5) repeat at least 5 times with 5 different cases to get an average
 
in my experience, I only use water volume as a means of grouping cases when I load. And that is, if I do it at all, which I generally don't. The variance in pressure is relatively small, and I would not assign a powder weight variance to a case volume variance. matching cases with like volume is only a means to minimizing one small aspect of variance from a precise target load. do that and all the other accuracy voodoo and you minimize more and more variables that will shrink the SD of your bullet speed and trajectory.
 
I would suggest that you buy your own copy of QuickLoad, and take the time to learn how to use it, and that is not something you do in one day.

Yes it is expensive, and you have to pay for the updates, but well worth it in my opinion. Always bear in mind, it is not a load manual and does not replace load manuals, but I have found it to be a valuable tool. Especially for the type of question that you posted. Case capacity DOES make a difference in pressures, but I don't know how "linear" these differences are, haven't looked at it from that angle yet.
 
"Taking short cuts with reloading can lead to unexpected results.
The best approach is, and always has been, is to work up loads from scratch with every change in components."

DON'T TAKE SHORTCUTS
 
It reminds me of one of the writings by Truthful James. If there is a difference how can they be the same? I know, it is assumed if the cases weigh the same the column is the same. Cases can have thick case heads with thin case bodies; cases can have thin case heads and thick case bodies.

Then someone has to decide if the length of the powder column makes a difference, I believe it does. I do not look for excuses not to sort cases. I sort cases.

F. Guffey
 
Then there are factors; what factors are affected by the difference between fire formed and full length sized/factory minimum length?

F. Guffey
 
If your charge is near max in a case with an internal volume of say 55 grains, and you then drop your charge only 1-1.5 grains in a case that has an internal volume of only 50 grains, then you have a good chance of being grossly over pressure. In a case that has less volume, I would always drop back 10% and work back up.
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This is what I'm trying to understand and after looking at my made up numbers I realized . a case volume that has 7gr less then another would likely be a HUGE difference .

So if a case has less volume by X amount then another being used . You should for sure reduce your charge and work back up . What if it has that same amount in more volume ? Do you still drop back down to minimum or 10% ?

All I'm really looking to understand is if the cases have the same case volume can they be loaded the same ? If so is there a direct correlation from water volume to charge weight ?

Lets look at it another way where it looks less like a short cut and more like trying to be safe . Lets say you have a case of unknown volume like most start with and your manual say start at 40gr with a max of 44gr . You later measure that case volume and it's 55gr . Some time passes and you get a new batch of brass and you check there case volume and there's is 50gr . Interesting thing now has just come up . If you were never measuring case volume you would just start at 40gr and start working up likely starting over pressure . But if you had been measuring case volume the whole time wouldn't those numbers tell you to start 15%+ lower rather then the 10% in the manual ???

You guys seem to only be looking at the negative aspect to understanding the case volume to charge weight correlation . Could there be a positive reason to understanding this info ?

I'm not looking to cut corners , just to understand more . Like I already understand even if there were some correlation it would be very powder specific . A fast burning powder will not have the same correlation as a slower burning powder in the same cartridge . So just saying X case has Y amount less volume then B case . Means you reduce the charge by Q amount period would be a very bad way to think of it .

I'm thinking the tittle should have been different and might have been better if it was more QL specific .
 
Metal God said:
1) If cases regardless of maker measure the same volume . Can they be loaded with the same charges ? Lets assume these are MAX loads for the question .
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It depends on how maximum was determined. If maximum was determined by how much the case head or pressure ring expanded, then no. You only know it is maximum for brass the same hardness. Harder brass will handle more, softer brass less. If the maximum was determined by peak pressure compliance with SAAMI standards or CIP standards, then, generally, yes. You may still get a soft case like a Federal that blows its primer pocket loose at some higher SAAMI pressures, but it should be good for at least that one shot.


Metal God said:
2) Is there a direct correlation from water volume to powder charge assuming you have a charge you know works well in a specific case . Let's say I have a 308 load I've used in X brass that has a water volume of 55gr . I want to load that same load in a different brand case but it's water volume is 48gr or 59gr ( just making up numbers here ) Is there a direct relation you can/should increase/reduce the charge based on the new internal volume case ?
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No. Not volume. But weight has a remarkable stable relationship, depending on the powder. Back in the 1960's, Wm. C. Davis, Jr. writing for the American Rifleman, worked out that you could estimate you needed to change the powder charge 1 grain for every 16 grains of additional brass weight, assuming that weight difference was all in the sides of the case so that with the bullet seated the same depth in both instances and with the head having identical dimensions, that brass weight difference was all in the powder space under the bullet. Since cartridge brass has a density of 8.53 g/cc, that's the equivalent of saying 1 grain change in powder charge for ever 1.87 grains of water capacity, or 0.53 grains of powder for each grain of water capacity. This was for IMR single-base powders of that day. The change is about right for keeping velocity fairly constant and letting pressure vary a little. It actually seems to be a compromise between these points.

What I would like is to do is keep the barrel time the same, so a sweet spot load with one case is still a sweet spot load with another. I find changing the charge about 0.7 grains for each additional grain of water capacity is often close to that.

In either case, use the change in powder charge calculation as a guess and work up to it rather than just believing it. Brass can fool you by differences in hardness and neck tension and so on.

I have modern 308 Win cases that weigh barely more than 150 grains. Recently someone reported a South African PMP 308 case that weight 194 grains. That's as much as Lake City 30-06 brass. 308 just has a huge spread, with most commercial cases in the 165 to 175 grain range and most military brass seeming to be around 176-186 grains. But the exceptions are out there, so you just have to check what water capacity you actually have, and go from there.
 
If the maximum was determined by peak pressure compliance with SAAMI standards or CIP standards, then, generally, yes. You may still get a soft case like a Federal that blows its primer pocket loose at some higher SAAMI pressures, but it should be good for at least that one shot.
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Yes that's what I meant . I knew if I would have left out max load in the OP I would have got more replies asking to clarify that . I should have said max pressure though but again I'd likely would not have included max pressure to SAAMI specs so I'd still get the question .

Your case weight conclusions are interesting for sure and finding modern cases weighing 150gr-ish is good to know . I don't remember what the headstamps were but I have weighed 308 cases in the 190's as well back when I weighed a lot of my cases .

FWIW I have a batch of Fed cases that weigh on avg in the high 170's and don't think I have any cases weighing in the 160's or less . I stopped weighing cases for the most part and don't use many commercial makers so me not having the lighter brass does not really mean much .

This just makes me wonder how much case volume matters with all these variables . Does SAAMI use a small chamber to represent the smallest possible case size ? When I say small I mean a chamber that would barely allow a case sized to SAAMI minimum to chamber .
 
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The last bulk purchase Winchester cases I bought (ab0ut 2003) averaged 156 grains, with a low of about 153 grains and a high of 159 grains. Others are reporting them up to 166 grains now. The 1992 Palma Match cases made by Winchester weighed closer to 150 grains, and someone wrote that they had some Hornady brass near that number, but I have no personal experience with it. The Lake City 7.62 brass I have is mostly 179-181 grains. Lapua 308 is at about 172 grains, and Remington about 168 grains. But that stuff's getting old, now. I made a big purchase of new brass at one point— a mix of LC, IMI, and Lapua— and have yet to fire all of it even once. So I've been out of the new brass market for 308 for awhile.
 
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