308 v 7.62 case capacity

chas442 said:

I have done a search and have not found any actual data in case capacities by different manufacturers. Has anyone actually measured case capacity of say LC and WWC versus Remington and Winchester?
Would you please direct me to where this can be located if it has been done.
TIA

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I doubt it would be useful data as they change with production runs. If you are looking to know for precision round development, I would suggest measuring the ones you have and grouping similar volume cases together for loading.

As far as measuring, there are a variety of ways to do it. Some fill cases with water and measure the weight of the water, some will use powder by filling the case and measure the weight of the amount of powder the case will hold. The powder method is my personal favorite. This is because I feel (I could be wrong) this best represents how the volume will work with a given powder. I should note, I do this after the case has been cleaned, sized and fitted with a loose fitting spent primer to plug the flash hole.

Myself and others have done it, you should also find data online. My findings like many vary depending on the brass and lot numbers. There is no greater case capacity in my findings in that one day LC 10 may have a greater volume than RP and the next day LC 12 has less volume than RP. It can be argued the mil spec brass is thicker and will have less volume but that doesn't seem to hold true. I suggest you try a few capacity experiments on your own using water and a scale. A drop of dish washing soap in the water (not enough for suds) will allow the water to come even with the case mouths.At one time there were several charts online calling out several case volumes. Here is one such example from Chuck Hawks. A Google of "cartridge case capacity chart" should get some results.

This is important:

I should note, I do this after the case has been cleaned, sized and fitted with a loose fitting spent primer to plug the flash hole.

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Cases should be sized and trimmed the same.

Ron

Like most generalities it's easy to find exceptions.

I've kept capacity records for years and the best bet is to measure the volume yourself.

My records show case capacities from 53.0 gr of water to 57.4 gr. Lapua is my favorite case but they are pretty pricey and their consistency changes over their life time. Even their brand new cases (100 per box) will vary by as much as 1 gr of water and after being reloaded about 4 times they don't produce groups that are substantially better than any other high quality brand of brass. But they have very clean flash holes and consistent dimensions when they are new.

A common brand that is pretty consistent in volume is Federal, I like them for most of my general shooting, I get them by recycling their commercial ammo, usually their Gold Medal Match ammo.

The trick isn't so much about what brand, most of them have pretty good volume consistency within lots, but stick with which ever brand of brass you prefer. Brand to brand volume variations can be quite large but within a brand it isn't so bad, especially within a specific lot number of that specific brand.

All that being said, I use QuickLoad to help build loads so I'm pretty picky about case volume information so when I start to load my ammo I'll always take a sample of the cases that I intend to use and test their volume, then I compare that to my records and see if I should expect any changes in powder charge - that's for my precision ammo. For hunting and plinking ammo I don't worry too much about volume issues, I pretty much just drop my preferred powder charge and top it off with a bullet.

Oh, and by the way, my records show that the brand of case that varies in capacity the most is WCC. They are tough cases that I love for general duty work but I don't use them for precision ammo. I need to be a little more specific, their volumes varied quite a bit over the years (from 53 to 57 gr of water) but within a specific year or lot they were pretty good.

chas442 said:

Has anyone worked with R.P. 308 brass? I have about 300 pieces of brass. Unfortunately there is no way to determine production year nor lot #. I'm dealing with indoor range pickup that I have accumulated years ago when working at a gun store/range

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Have I worked with Remington brass? Yeah, it reloads much like any other commercial average brass. I have never had any problems or issues with it. The ones I have currently laying here seem to average about 170 grains less primers. Not much else I can say about the stuff.

Ron

I think its a waste of time to measure case capacity unless the cases are all full into a full length sizing die. That's the only time their outside dimensions and shape are the same across all cases. Then their inside volume is the only variable. Cut the top of the die off 1/8 inch below the case mouth so it's easy to do.

Or.....

Weigh empty cases then sort to batches with a 1% spread in weight. Close enough For all practical purposes.

I would sort by headstamp first. If best accuracy is a goal, then sort each headstamp by weight to groups with a 1% spread.

Weight isn't directly related to volume, there is no substitute for measuring the volume.

Weight is directly related to volume. Calculate the chamber volume, then subtract the volume the case has based on its weight. Tables show the weight per volume unit of typical cartridge brass.

Actually no, weight is not directly related to volume. Take two cases that weigh exactly the same and crush one of them, their weight will still be the same but their volume wont be the same. Look at the formula for the volume of any geometric shape and you wont see weight involved in any of the equations.

Robert Johnson researched the concept (Case Mass vs. Case Volume by Robert Johnson) and proved that there is no direct relationship between weight and volume. From his data he proved that cases of the same volume can weight differently. The graph below shows cases of the same volumes having different weights.


Additionally there is a published article at RealGuns.com entitled "Handloading... A Sorted Story Part I" and "Handloading... A Sorted Story Part II" in which they clarify that while case weight will show a general trend in case volume it wont actually predict volume accurately. In so far as the weight vs volume issue they conclude;

Sorting to uniform case capacity is a key ingredient in achieving consistent velocity. Dimensional and weight sorting will not lead to that determination, which means only one approach exists, wet measurement. There is just no other way to determine if extra weight found on a scale is to be found in a case wall where it will influence capacity, or in web or rim where it makes no difference.

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Seems to me it all depends on when case volume is measured. When all cases' outside dimensions are the same at peak pressure in the chamber or full into a sizing die versus their shape outside of such constrictors. One way has more volume changing variables than the other.

Read the documents that I mentioned, the cases were all resized and cleaned before they were weighed so outside dimensions weren't an issue. The problem is that cartridge brass, like all metals, isn't exactly the same, the amount of constituent metals can vary slightly which changes the characteristics of the brass. Also, the thickness of the brass isn't always the same, regardless of whether it's new or used. The area around the web is where you'll find the most variation, sometimes the web is thicker and the taper between the web and the walls is different, these all change the characteristics of the case.

What's confusing to most people, and where this myth started, is the fact that in general terms you can use the weight as a guide to volume changes on a large scale but when you start to drill down to exact weights and volumes there is no direct correlation. In other words, if you want to classify case volumes by creating weight groups of 3 or 4 grain increments and then average the volume changes you will get fairly decent correlation between the two. But if you create weight groups of 1 grain increments the volume wont follow the weight reliably.

A hunter that just wants reasonably consistent ammo can just use cases from the same manufacturer in the same lot number and get reliable results, he doesn't need to compare precise volumes. On the other hand, if you are a long range competition shooter then you'd be better off measuring the volume of every case you load because weighing them wont provide the consistent volume that you need to be produce your precision long range ammo.

So are you saying that facts and data don't matter?

Results of weight-sorted brass performance (in competition and otherwise) is "facts and data."

ATLDave said:

Results of weight-sorted brass performance (in competition and otherwise) is "facts and data."

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No, that's anecdotal evidence not data.

That's absurd. Of course is "facts." Anecdotes, as long as they aren't fictional, are facts. And large sample sizes in controlled conditions - which describes serious competition - allows for the aggregation of specific facts into a collection of data. Thus, the performance of weight-sorted cases in large numbers of competitive matches is "facts and data."

Maybe what you mean is that these facts and data are not relevant to, or conclusive to, how weight and volume/capacity relate. And that may be true, insofar as it goes. But if the question is whether accuracy is impacted in any non-theoretical way by the non-correlation between weight and capacity, it's highly relevant.

Read my post carefully, it's only 6 words, I didn't say anything about your proof not being a fact, I said that it's not data. I don't know if your misquote was purposeful or simply a mistake. I mean what I said, you said that the results of weight-sorted brass performance (in competition and otherwise) is "facts and data.", I said that it's not data, it's simply anecdotal evidence, I didn't say anything about it not being factual. Anecdotal evidence can be factual but not accurate, simple observations are not scientific data, they are too easily influenced by the observer and the process used to observe. Data is derived from controlled experiments.