If they have been fired in the same chamber it should be close but then you have to think about different lot numbers as they change the forming dies every couple of days when they wear and you get a case from the front of a lot with a new die and the end of the lot with a tired die they can vary.

 

What happens when you ASSume blade.....

Unless you know the specific machines that built them, the tollerance for those machines, the construction of each lot of brass, you can't say that.

The more pertinent question may be, whether or not it matters for your particular style of loading.

A few years ago I did a post on this topic.

I load by volume, and not weight. I refuse to segregate, weigh, measure, or show preference to any brass. So my 308 has headstamps that range from the 1950's to almost present. Both military and civillian. Any of those cases loaded the way I do, will keep MOA in my rifle out to a mile.

Are they the same? probably not. Does it matter? IME, no; But as always, YMMV

 

Are they the same? probably not. Does it matter? IME, no; But as always, YMMV

I've posted the weight references for a lot of .308 brass several times. No they're rarely the same. Closest is M118 to M80LR. EVen IMI match brass is a tiny bit heavier.

Decrease the volume, increase pressures

 

Well, one could "assume" that any two cartridges for the same chamber have the same volume, but without checking, you can't really be sure. About the only good generality you can make is that if two cases from the same lot weigh the same, they probably have the same volume.

 

First of all im not going to load anything on mere assumption. So let those eyebrows rest. Lol .The reason im asking is i have a bunch of different headstamp brass for .270. I been trying to use up some of this and have a little a load i put together for a friend to hunt with. I think i had 30 pcs of one headstamp . its not going to long and the brass will be shot. I found a different headstamp that weights exactly as the others. I was wondering if they would produce close to the same result as the other brass. I would think they would be the closest in volume i could get to what i had.

 

I concur with Darkker. With .308 brass, I have never been able to measure the difference in shooting results between different headstamps/lots of brass. Some have lasted longer than others, but no measurable difference in punching paper. Now, with .223, I have seen some differences, but I believe that is because with the much smaller case, thicker brass will have a significantly lower volume. But that difference has only been demonstrated when I was loading for maximum velocity with full cases of powder. At more moderate loads (and just as accurate) I have found no real difference at the target. And since I now shoot lots of cast in every caliber with load densities in the 50-75% range, there seems to be no differences at all in accuracy or velocity.

 

I'm thinking they're going to produce close to the same accuracy as the others. I'm shooting pretty fair groups in both 300Sav and 22-250 where there has been some mixing of headstamps, despite my efforts to keep them batched. Then again, I don't weigh my brass of one headstamp unless I can't sleep or am awaiting a phone call.

I'm thinking they'll be good and you'll know as soon as the targets are examined.

 

I found 3 different headstamps that the case weighed within a grain of each other. I sized them to fit the chamber, clean them, seated a primer and weighed again then filled with water and weighed them again. There was a .5 grain spread between the 3 different headstamps.

 

The 3 headstamps where federal, ww super, frontier

 

That won't mean much in the grand scheme of things. So I would probably shoot them all with the same loads. Half a grain of water isn't much when you have around 60 grains of water capacity in a .270.

Edit: careful with the Federal brass. It has a varying reputation for quality.... I have some that has shot great, and some that gave a lot of trouble. Some of it is pretty soft.

 

this is old brass thats been well preserved. I will keep a good eye on it.

 

Winchester and remmington where the heaviest cases i weighed. They where about 6 gr. Apart. Hornady headstamp was the lightest. It weighed in at 20 gr. Lighter than remmington. The 3 i weighed where right in the middle

 

If two different head stamps have the exact same case weights could one assume they have close to the same volume?

No, but if the reloader chooses to check his loaded ammo for the last time before pulling the trigger: knowing the weight of the case is a ‘must know’ thing.

Long before the Internet there was a shooter/reloader/writer that purchased 500 cases from one lot. He sorted, measured and weighed and then loaded and shot and then started over. When he was finished he settled on 47 cases. He decided the 47 cases were perfect, load them; shoot them.

The other 453 cases worked but required tweaking. Some of the worst of the rejects worked perfectly and just as accurately if he indexed the case in the chamber.

Some of the cases did not make it to the final 47 because of the powder column. Some of the powder columns were not straight meaning the case body was thicker on one side than the other. Some of the cases had long powder columns and were smaller in diameter than other powder columns in other cases. Some of the cases had powder columns that were short and large in diameter.

When assuming reloaders assume military brass is thicker because it is heavier than commercial brass. At best that can only be a half truth. I have military cases that have a case head thickness of .200”, I also have R-P cases with a case head thickness of .260”. My military 30/06 cases have a thin case head and a thick case body. My commercial R-P cases have a thick case head and a thin case body.

F. Guffey

 

Winchester and Remington where the heaviest cases i weighed. They where about 6 grains apart. Hornady head stamp was the lightest. It weighed in at 20 gr. Lighter than Remington. The 3 I weighed where right in the middle.

First of all I am not going to load anything on mere assumption. So let those eyebrows rest.

Blade, when I want to load the lightest case I go to the Winchester drawer; no matter the head stamp when it ‘came’ to the lightest case with the most volume it was Winchester, WW, WRA and Western cartridge Company.

F. Guffey

 

And what difference would any of this make in accuracy out to, say, 300yds?

 

For an average game hunter, likely nothing they would be able to notice.
For a serious shooter/target competitor, potentially a big difference.

As with everything, what your definition of accuracy is, will play a very large part in what the outcome could mean.

 

This question can only be answered with opinions and anecdotes. You're no closer to the truth than when you started. If you really want to know, do your own testing and see what you find. As the old saying goes, "YMMV".

Ray

 

Already have Ray. Nick and I talked about this last year and I did do volume checks.

 

This article compares weight and volume of cases in 243 Winchester. He has two lots of Winchester headstamp cases. Both have average case water overflow capacity of 54.8 grains, but one lot's average weight is 158.58 grains, while the other averages 166.44 grains.

Pretty much the only way that is possible is if one lot has its head dimensions on the thick and heavy side of the specs while the other is on the thin and light side. The SAAMI standard drawing tolerances allow the rim diameter a span of 0.010", the head forward of the extractor groove a span of 0.008", the diameter the extractor groove a span of 0.020", the rim thickness a span of 0.010", the extractor groove length a span of 0.010", the relief angle forward of the front edge of the extractor groove a span of 6°, and the chamfer on the back edge of the rim a span of 20°. None of those dimensions affect the internal volume of the case because, with the single exception of the primer pocket, internal volume all happens out in front of the head. So the head is where differences in tool sets throw the weight and capacity correlation off.

A couple of guys have looked for quick ways to determine case capacity without resorting to the slow process of measuring actual water capacity, but I am unaware of such a method that is practical that has accuracy that is adequate. If your scale has a lot of capacity, you could buy a bag of small ball bearings and they should be consistent enough to give you a water substitute that is easy to fill and level and should get you close enough. You may need to vibrate them to maximum settling by flicking the cases with your finger or touching them to your vibratory tumbler.

A fellow on another board was looking at a method of determining case volume with air, but the price of gauges with high enough sensitivity and resolution was putting him off. I suppose he was considering a variation on the gas pyncnometer for which you would pressurize a known volume, then communicate the case with it to observe how much the pressure dropped when the gas was allowed to flow from that volume into the case. The case wouldn't get wet, but I still don't see anything really quick and simple coming out of that arrangement.

If you sort by weight there is usually a correlation, but not a great one. I tried a small sample of a variety of .308 cases, and found weight-based volume prediction (compared to water measurements) only found the capacity difference about ±20%. It would have predicted 0.92 grains difference in case water capacity for the 243 Winchester brass mentioned in my first paragraph and been completely wrong.

 

This article compares weight and volume of cases in 243 Winchester. He has two lots of Winchester headstamp cases. Both have average case water overflow capacity of 54.8 grains, but one lot's average weight is 158.58 grains, while the other averages 166.44 grains. If your scale has a lot of capacity, you could buy a bag of small ball bearings and they should be consistent enough to give you a water substitute that is easy to fill and level and should get you close enough. You may need to vibrate them to maximum settling by flicking the cases with your finger or touching them to your vibratory tumbler.

Heck of a good idea Nick. I've kept the sample cases aside. When the weather breaks something to look into .

 

Nick, Were those two cases fired in the same chamber. It is the volume of the chamber that makes the difference not the volume of the unfired case. The case when fired will expand to the volume the chamber permits.

Almost all cartridge brass has the same density (specific gravity). If two cases of the same weight are fired in the same chamber there is little opportunity for difference in fired volume except for difference in rim and extraction groove. If that is where the extra weight comes from it would not effect fired volume. In any case the difference would be so slight that it should be well be within the cautionary limits of "start x% below max"

 

Nick, Were those two cases fired in the same chamber. It is the volume of the chamber that makes the difference not the volume of the unfired case. The case when fired will expand to the volume the chamber permits.

Apologies. I went back and looked and I had never inserted the article link. I've edited it in now. Here it is again. It was not two cases. It was average values for two lots of cases. He resized them all in the same die before measuring, probably thinking to give a number everyone could use, regardless of the size of their particular chamber. Unfortunately, due to differences in springiness from differences in work hardening from differences in load history, neither resizing nor once-firing in the same chamber gets you a perfect comparison. You would want to pick a chamber, then neck-size-only and keep firing until all the cases were just getting snug in the chamber or at least had identical exterior dimensions. That should remove comparison error; something to take springiness out of the equation, whether it is spring-back coming out of a sizing die or out of a chamber.

Almost all cartridge brass has the same density (specific gravity).

This article shows, within a couple percent, Remington and Federal are 80:20 brass (80% copper, 20% zinc), aka low brass, for which the density at 68°F is 8.67 g/cc. Winchester and S&B (and Lake City, though it wasn't in the experiment) use 70:30 brass, aka cartridge brass, for which the density at 68°F is 8.53 g/cc. Some older Lapua brass and some wartime manufactured brass is 60:40 brass, aka Muntz metal, for which the density at 68°F is 8.39 g/cc. So the expected weight of Federal and Remington brass for identically dimensioned cases is about 1.6% greater than Winchester or S&B (or LC, if you have a military chambeing), or a little over 2½ grains in the example in the 243 Win cartridge case article. That is close to what you'd expect in .308 Win, too, since it's close to the same weight. 2.5 grains of case weight, even when it does represent a difference in water capacity, is not significant in most rifle cartridges. Based on William C. Davis, Jr.'s old estimate of 16 grains of brass weight volume for each grain of powder charge adjustment, it would require about 0.15 grains of powder to make up the error in most medium power rifle cartridges. Most loads are not sensitive to a charge error that small.

If two cases of the same weight are fired in the same chamber there is little opportunity for difference in fired volume except for difference in rim and extraction groove. If that is where the extra weight comes from it would not effect fired volume. In any case the difference would be so slight that it should be well be within the cautionary limits of "start x% below max"

If you read the second paragraph of my last post, I mentioned not only the rim and extractor groove depth and shape, but the diameter of the whole head, which can change 0.008" without affecting internal volume. But you got me curious. My CAD software calculates volumes, so I decided to draw the minimum and maximum head and see what sort of volume difference I got. It turned out to be about 0.82 cm³, or 7 grains of brass if the material is 70:30 brass in both cases. This comes close to the difference in the two lots of 243 Win cases. I used 0.2" case head internal height to get this difference.

In any event, somewhere around 7 grains of case weight difference can occur without case volume change in a case with a 0.473" head. Some cases have more variation than that, with .308/7.62 cases with numbers up to about 32 grains of difference (1992 Palma Match .308 Win at 150 grains, vs IMI .308 Match a 182 grains). In that case you may have anywhere from about 23 to 32 grains water capacity difference if the alloys are the same. You are then looking at about 1.5 to 2.0 grains of powder needed to keep performance constant.

Anyway, this may give you some sense of numerical values possible in the .473" diameter heads with large primer pockets.

 

Watch that Frontier brass, that brass runs much higher pressures than F.C., R.P, Hornady, or Win. does.

It's been a good number of years back, but I had sorted some brass for .270, and the Frontier was in the same ball park as one of the weight groups I was working with. But because I didn't measure volume, I experienced some extreme pressures, and supporting velocity that was much greater than the other brass in that weight group. Herter brass has exhibited the same characteristics, and I'm sure there's other head stamps out there that don't correlate with some of the others.

This is why I only use matching head stamps, and unless they are from the same lot, I sort according to volume, not weight.

SMOA

 

frontier is what the load was worked up with so i should be ok.

 

I was curious about that too. Sounds like lots of work checking each case to sort by volume. Maybe you've got a good system to try.

 

Cleaned, sized to chamber, inserted primer, weighed case, filled with water and reweighed, subtracted the difference. Filled it with a dropper and tamped as i gradually fill. Thats the only way i know of. I just did the 3 cases. I weighed them before i seated a primer to make sure they weighed close to the same the difference in water weight and case weight wasnt to far off from each other. Im thinking weighing the cases and keeping them a 1/2 gr. Apart would be fine. The jury is still out on that. Im sure there is a difference somewhere. Will see.

 

Unclenick has a better way of doing this, let's see if he'll explain the best way to do it with water. I'm interested in trying it with BBs to see if it's more accurate. I have to wait till I dig out.

 

No, I have done extensive and time consuming tests between case weight and corresponding volume. Assumptions in this area can be correct, but, in most insrances, no 2 case brands had similar volume even when weight was very close
It is also apparent ocer a chrony, load a few different brands of cases, and fire a few of each over a chrony, I bet they differ by some, or a lot!

Cheers.
.

 

In about 1970, I separated 6x47 cases by weight into three groups- Light, Right and Heavy. Light and heavy were made up of the 10% of cases in those areas with 80% of all cases in the 'right' category. Then I shot groups and compared. I've never separated cases of the same make again. I'm sure case weight is on the list of a hundred things that make groups big, but it can't be in the top eighty-five in importance.

 

The federal and ww super brass where 13 fps apart.

 

90 fps using h 1000.

 

I have weighed and done water capacity tests on hundreds of various cases and my findings are that what you ask is not necessarily true. However I have found that 223 cases weighing +/- 95-96gr and cases weighing 108gr have had the same internal capacity. YMMV.