Water weight differences between brass.in my .270

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Gyrfalcon

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I have one batch of .270 Win Nosler brass that weighs 201 grains/case and water weight of 65.80 grains
Another batch of Nosler brass that weighs 178 grains/case and water weight 70.96 grains
That is a 5 grains difference in water capacity.
I use in my 178 grain brass a load of 54 grains of H4350 for 3060 fps under a 130 grain Nosler ballistic tip.
Anyone knows how much H4350 powder difference there should be between the 2 different cases, due to the 5 grains in water weight?
Of course I can do a ladder test between the 2 cases, but in these days of component scarcity I try to preserve as much as possible. Can the percentage of the water weight differences be extrapolated to the powder weight? Is there a safe way to calculate the needed difference?
 
The differences that you found are pretty drastic!! Last December, I was trying to figure out if nny headstamp 9.3x62 brass was same or not as PPU 9.3x62 brass - those were headstamps / brands used at different factories of the same manufacturer, at one time, I think. I weighed 5 empty cases of each kind with a fired primer in them - they each had been full-length resized (without de-priming them), since not all were fired in my rifle. All cases were trimmed to same overall case length. Then filled with water to the brim and tried to get meniscus the same - was fairly tedious to do - I used a hypodermic syringe to "top up" to get meniscus similar one to other - weighed full of water - deducted the "dry" weight of each and got the following - for 5 cases of each type:

nny - 73.1, 73.9, 72.8, 73.3, 74.5 - “grains weight of water”. average - 73.52 extreme spread is 1.4

PPU - 72.7, 73.2, 72.8, 72.7, 73.3 - “grains weight of water”. average - 72.94 extreme spread 0.6

So the difference, in average, between the two sets of 5 cases each was .58. That is less than the extreme spread of either set of 5. So, I concluded there was not a very significant difference between the two headstamped sets. I suppose that I could have continued and done 25 cases each and got different values - what I did do, was "close enough", I thought, for my purposes. But you are reporting a much, much larger difference with the same headstamps - as if you have cases for two different cartridges!!!
 
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I would load 3 of each and chronograph them while shooting and observe speed and impact. Adjust accordingly. It would be hard to determine where the difference of volume is at in the case to know how many kernels of H4350 would fit in it. Compare a new unsized case water weight with a fired sized one. ( same batch ) Then see how much powder takes up that space in each one just to get a reference. However I would just match fps.
 
OP, the issue you mention isn't as uncommon as many believe.

If you want to see the actual "real" difference in the field, load up five of each with the same component lot of bullets/primer/powder, take them to the range and check the velocities and see where they impact on target.

Some rifles will just gobble up both rounds and groups won't be affected. Some can be picky.

That's the only way you will find out if your rifle magnifies the difference.

Most of the time, people that are anal about accuracy (including myself) will keep brass lots separate and even then, they will separate the weights within the lots into usable quantities.

Bench Rester types used to keep all of their brass lots within +- 1 grain weight batch, weighed "after" turning the necks down to fit their chambers/dies.

In the real world of hunting requirements, that much anal is not necessary

I found, after several years that keeping lots of brass separated was about as much as I was willing to do and still do.

If the cases from each of your lots are consistent to each other, keep them together and don't mix them up with each other.

Now, depending on how tight the tolerances of your chamber are and the quality of your handloads go, such as your run out, consistent bullet weight with consistent jacket thickness, etc, the weight difference between your lots of brass may not make enough of a difference in POI to worry about.
 
I feel that water weight just adds another layer of unnecessary complication to your comparison. I just weigh the brass and don't bother with water, since water volume / case volume directly correlates to brass weight. I don't shoot a .270, but the difference between brass weighing 15 grains difference when shot in in both my 30-06 rifles equals about 2 grains of H4350 under 180 grain bullets.
Your caliber, your specific rifle, and the bullet you use will make your results vary from mine. You have 23 grains of brass weight difference. I'd predict you will need to adjust 2 grains of powder or so. A chronograph is the only sure way to tell, quicker and more useful than a long distance shooting "ladder test" . In any case it is definitely worth keeping those 2 brass lots separate.
 
How do you know that the weight of the brass is or is not at the case head or related to case capacity. I have never ( yet ) had brass that shot majorly different between lots, or it was very little. Case capacity trumps case overall weight. Heck the brass itself may have a different makeup percentages that effect weight???
 
Since the outside dimensions have to be the same, internal volumes will be different. Stands to reason. When I first got my 5-0-5 after using a little Lee, I weighted some of my 30-06 . I found a 30grain + difference.
 
Gyrfalcon said:
I have one batch of .270 Win Nosler brass that weighs 201 grains/case and water weight of 65.80 grains
Another batch of Nosler brass that weighs 178 grains/case and water weight 70.96 grains
That is a 5 grains difference in water capacity.
I use in my 178 grain brass a load of 54 grains of H4350 for 3060 fps under a 130 grain Nosler ballistic tip.
Anyone knows how much H4350 powder difference there should be between the 2 different cases, due to the 5 grains in water weight?
Of course I can do a ladder test between the 2 cases, but in these days of component scarcity I try to preserve as much as possible. Can the percentage of the water weight differences be extrapolated to the powder weight? Is there a safe way to calculate the needed difference?
Click to expand...

If you have both cases and H4350 powder, you could fill each case with powder and weigh it. No extrapolation needed.

I expect the capacity difference would 2-3 gr of powder.
 
I have been using Gordons reloading tool (for about a week)..... down load it :) its free

reduce your charge and work up to a max of 51.9g ...with the 201g case............. but you know what they say about internet reloading data.... do not use it

there is a lot of variables so use Caution.

you are supposed to use fired cases h20 volume... is just one example
 
downwindtracker2 said:
Since the outside dimensions have to be the same, internal volumes will be different. Stands to reason. When I first got my 5-0-5 after using a little Lee, I weighted some of my 30-06 . I found a 30grain + difference.
Click to expand...

Not all outside dimensions will be exactly the same…. measure the diameter of a bunch of case heads, where the head stamp is, I use Hornady, and I found one new brass that would not chamber, it turned out to be the diameter of the case head was out of spec, I sanded it down a bunch and it chambered. I noticed when checking a bunch of them, the rest were good, but nowhere exact with each other. Maybe Lapua, Peterson, Alpha are better, better be. I had thought Nosler sourced out their brass?? Different suppliers then. OP, I have an old box of new 270 Nosler brass, I will weight 10 tomorrow and see what they weigh. ( bought from Wholesale sports )
 
Lead Hammer, for practical purposes case capacity IS the same as case weight. In cases trimmed to the same length. There is very little difference in the proportions of copper and zinc and lead in cartridge brass alloy. Brass shellcase metal is typically 70% copper, 30% zinc ( aka cartridge brass), no lead added. So bulk density is nearly identical between lots or between brands. What does vary is the hardness of brass cases, depending on how the brass was worked and / or annealed. I won't waste my time with calculating case capacity in grains of water, but if it gives you joy, why not! Just don't expect more precision than simply weighing the brass. And it makes no difference to case capacity and the pressures produced whether or not the brass weight is in the walls or the base of the case. It MAY make a difference if the base is too thin at the web to hold the pressure produced, but that's another question.

I certainly have seen practical differences in brass that is heavier and at the same time softer ( Example Federal .30-06 ) compared with brass that is lighter and harder ( for example Winchester .30-06) A difference of two grains of powder at maximum safe pressure or 100 fps is not unusual at all.

Brass that is different in weight but similar hardness does not show as pronounced a difference in maximum safe charge, but it will still show a velocity difference. In my experience RWS brass is both thick and hard. It can withstand higher pressures than most but requires less powder to get there. Norma brass is a little on the soft side, but is not too heavy/thick so normally I can use the same charge loading Norma brass as I do in Winchester and Hornady, which are relatively "light" in weight.

For big game hunting loads, where extreme precision is not my main goal but reliability and function are paramount, I group my .30-06 brass into two groups as follows, divided by average case weight:
178 gr. - Hornady
181 gr. - Norma
187 gr. - Winch.
- and -
195 gr. - Imperial
198 gr. - Fed & Lapua & Rem
199 gr. - PMC

And please note that very old lots of brass in the same brand sometimes vary from these averages. Hope that helps!
 
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Longwalker, I get what your saying. Along with less capacity at rest, thicker brass reduces expanded under pressure case capacity as well however extra weight on the case head between lot numbers won’t change anything but the scale weight. I’m certain water volume is more precise than just weight alone, but the difference might mean nothing in the big picture.
I don’t measure case capacity or brass weight. When I get a new barrel then I will just get better brass, and still not weigh or volume test them.
 
Weighing brass has a few uses,one like the OP pointed out differences in powder amounts, another, ABC brand weights say 175 and XWZ brand weights 176 I can treat them as the same . But for precision rifles, you would want them all to weigh in a narrow range.
 
Only time I've seen that big of a difference in '06 sized cases was Hornady Superform brass. That stuff weighed less then most 308 brass.
Prvi is heavy brass, in my 7mm Rem, Norma weighed in at 218gr, prvi was 270gr.
 
Usually the biggest difference in brass weights are between milsurp and commercial cases.

7.62 Nato IVI for instance, is significantly heavier than Norma 308Win. Privi 308Win is almost as heavy as IVI.

There have been many articles written, warning hand loaders to reduce their powder charges by 5% if they're using milsurp brass.
 
I’ve been playing with Gordon’s reloading tool for about a month now.
When I open GRT and plug in the components you have given it gives me a velocity of 2951 ft/s and a maximum pressure of 50261 psi. before taking into account your case capacity.
Their case capacity is 71.5gr.
When I adjust case capacity to 70.96gr their predicted velocity is 2963 ft/s. And a maximum pressure of 51109 psi.
When I run their correction program for your velocity of 3060 ft/s the maximum pressure rises to 55740 psi.
There are still no high pressure warnings but you are within 10% of absolute max pressure.

As soon as I reduce case capacity down to 65.8gr I need to reduce powder capacity down to 51gr to be within 10% of absolute maximum pressure and the predicted velocity is 3010 ft/s. and pressure is predicted at 55192 psi.
If I try to increase the load to 31.8 gr achieve a predicted 3060 ft/s maximum pressure prediction increases to 58036 psi and warnings of over pressure begin to pop up.

I would probably start around 48.8 gr working up in .3 gr incriments till I got what I was looking for as far as accuracy or till you get pressure signs.

You have to remember that everything I wrote above are just predictions which can be right or wrong.
It’s you gun and your face on the line and nobody can make that decision but you.
 
That weight difference is about the same a a military 308 case compared to a commercial case. When switching brass, I add or reduce powder by 2 grains.

The case forming dies get changed from time to time, and the brass sheeting can vary a bit, lot to lot. This is why makers use lot numbers. each lot is unique.

There are usually multiple machines making cases and the output gets blended. This is why it is wise to weigh and sort your brass.

Match brass may only come from one machine. Less variation.

One maker had a case machine dedicated to making cases, but the die that punched out the little brass slugs (look like thick quarters) punched out two at a time. There was a noticeable difference in the two slugs. After the cases were formed on a single machine, I was able to sort the brass cases into two distinct lots (by weight) , all based on which machine punched out the initial slug from the brass sheet.
 
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