Volumetric Measurement of a Rifle Case Does It Matter to Accuracy

[Load Master]

Here at The High Road, around the internet and forums you will find countless way to measure rifle case volume. There are YouTube videos and write ups on this subject. Some use water, some use powder, some measure case weight, and spend a lot of time sorting brass with the hope of improving accuracy. In this thread I am hoping to focus on the benefit, perceived benefit, or if it is a waste of time.

Please share your experience, findings, and or belief on this subject. Better yet, if you have run any type of test, please provide your findings. Curious minds are interested.

When posting a reply start off with one of the three options below:

• Benefit
• Maybe a Benefit
• Waste of Time

This will give us a "Head Up" on where you are headed with your post.

I'll share in the thread once we have things on the way.

 

[Bart B.]

As cases unprepped nor sorted any way can shoot good bullets from properly full length sized cases stuffed the right primer and powder in good barrels inside an inch at two hundred yards, I consider sorting cases by any metric a waste of time for any use at ranges up to 600 yards with ordinary rifles.

https://www.thehighroad.org/index.php?threads/308-v-7-62-case-capacity.819112/

 

[Reloadron]

• Maybe a Benefit

• Waste of Time

I see it as somewhere between the two. When I load I really do not care what the case volume actually is. What I would like is uniformity. I try to sort by head stamp, especially with using military surplus brass. Recently I have been working through a pile of WCC 10 brass which on average weigh about 177.9 grains. I really don't care what the volume is because as long as the cases are uniform it matters not to me. I have yet to find a loading manual which identifies brass and list different load data for different brass. Occasionally you will see a comment like this:

Master Po's comments
These loads only duplicate military spec. velocities for the given bullet weight, using commercial cases and powders. If you are using military cases, drop all charges by 2 grains.

But for the most part most loading manuals do not specify brass. Can't change the volume of a case anyway and one has to wonder, with everything else to be concerned with, how much does it really matter? Anyway, again I really do not care what the actual volume is, I care about uniformity case to case and that's about it.

Just My Take....
Ron

 

[Load Master]

But for the most part most loading manuals do not specify brass. Can't change the volume of a case anyway and one has to wonder, with everything else to be concerned with, how much does it really matter? Anyway, again I really do not care what the actual volume is, I care about uniformity case to case and that's about it.

Ron,
You mention not caring about volume. What feature case to case matters? What are you looking for when matching cases?

 

[Walkalong]

I'll continue to weigh cases and sort that way, as well as adjust charges by it.

Water is heavy and unless each case is filled exactly like another the variance could be suspect as far as I am concerned.

Most rifle shooting cannot take advantage of segregated cases, no mater which method is chosen.

 

[hdwhit]

Load Master wrote:
In this thread I am hoping to focus on the benefit, perceived benefit, or if it is a waste of time.

I think it all depends on what you are trying to accomplish.

• If all you want to do is poke holes in paper targets at 100 yards and occasionally trek off into the deer woods a time or two each year then other variables that affect accuracy are going to have a greater influence than case capacity.
• If you want to reach out several hundred yards and try to shoot five shots and have one hole, then uniformity in all aspects of your ammunition becomes more important and because of the potential influence case capacity can have on how fast the powder charge combusts which can influence velocity, perceived recoil and follow-through, having cases that have nearly the same volumetric capacity becomes more important.

In my case, I sort my brass by headstamp because i have noticed that there are differences between manufacturers in how the primers are crimped, how easily the cases slip into the shell holders, and the number of times I can reload it before the neck splits or the primer pocket enlarges.

 

[Reloadron]

Ron,
You mention not caring about volume. What feature case to case matters? What are you looking for when matching cases?

OK, when I size a case I size them all the same. I also keep the head stamps all the same. OK, I will share with you the beginnings of a little experiment I just started based on the last thread on this subject.

I have sized and trimmed 10 cases each of R.P., Winchester, WCC 10 and LC 13. I will be adding 10 cases of Federal tomorrow. All the cases were trimmed to a 2.005" C.O.L. and all were sized to 1.630" base to datum on shoulder. In other words the outside dimensions of the cases are identical. I have also weighed the cases, less the Federal which I'll get to tomorrow. On average R.P 170.1grains, Winchester 164.4 grains, WCC 10 177.9 grains and the LC 13 178.8 grains. Interesting was the STD DEV OF 0.620 1.334 0.586 1.870 where the WCC 10 has the tightest deviation. Tomorrow the Federal Brass will get tossed in the mix and weighed and sized.

Obviously I know these cases have volume and tomorrow I'll get to that part, More as a matter of knowing the volume. More as a guess but just looking at weight and the standard deviations so far the WCC 10 which has bee serving me well will likely deliver the most uniform volume but we shall see.When all is said and done I want small numbers for standard deviation. By tomorrow I should have the volume numbers on all 50 cases,. Then I will hand prime them using CCI BR primers trying to keep the priming uniform. I will powder charge each case identical and seat either Sierra 150 gr BTHP Match or 168 grain BTHP Match. I'll run them over the chronograph and save the data.

I am not saying that case volume is unimportant, I am saying I really don't care what it is as long as I get uniformity case to case as I charge the cases. I want my powder uniform, my bullets uniform, my primers uniform and my neck tension uniform, We shall see what we get, I would like a nice dry day around 70 Degrees F,

Ron

 

[Reloadron]

Water is heavy and unless each case is filled exactly like another the variance could be suspect as far as I am concerned.

Yeah, and I dread doing 50 cases tomorrow. But it is my little science experiment,

 

[Bart B.]

As one of the case variables is its outside shape, the case should be full into a full length sizing die when it's filled to some point. Oval shaped case bodies hold less water than when round. Case headspace can vary .004". Sorting by weight to a 1% spread is ok for ranges past 600'yards.

Regarding case weight and charge adjustment, people who've done pressure tests see about 7/10ths grain charge reduction for every 10 grain increase in case weight to keep peak pressure the same. This is based on typical minimum to maximum charge weights listed in reloading data.

 

[cfullgraf]

Regarding case weight and charge adjustment, people who've done pressure tests see about 7/10ths grain charge reduction for every 10 grain increase in case weight to keep peak pressure the same. This is based on typical minimum to maximum charge weights listed in reloading data.

Does this "rule of thumb" work the same for a 223 Remington sized case as for a 308 Win sized case?

 

[WelshShooter]

Waste of Time

Before you even start batching cases by equivalent internal volume you need to resize all brass to the same dimensions (e.g. full length sizing), trim to the same case length, neck turn, uniform the primer pocket and adequately clean the case (in the instance of using fired cases, because the carbon build up on the inside will restrict internal volume). The easy answer is to buy quality brass, such as Lapua, and not bother with batching your brass at all!

If you are doing F-class or any other sort of long range precision shooting, then you would probably care about batching brass, even Lapua brass I suppose, in order to ensure consistency between shots. If you are going to batch your brass, you should also uniform your bullets by trimming meplats, pointing the bullets and sorting them by base to ogive followed by weighing every single powder charge when making ammunition. For the average shooter, this is overkill.

 

[Bart B.]

Does this "rule of thumb" work the same for a 223 Remington sized case as for a 308 Win sized case?

Yes, close enough in my opinion. Others have said to use 4/10ths grain change per 10 grains of .223 case weight based on a percentage change of case and charge weights.

Both cartridges' charge weights are about 1/4th that of their case weights; a very interesting comparison. As are the weights for my 30-338 Win Mag; 65 grains of powder in 240 grain cases.

223 case weights:

http://www.6mmbr.com/223rem.HTML

I read some time ago that someone made pressure and velocity tests with a cartridge changing only the large rifle primer. Quite a spread, as I remember.

Average velocity spread for the same rifle and ammo can have over 50 fps spread across several people.

 

[Offfhand]

Waste of time!!! Two big reasons: (1) being that 99.9999% of rifles are incapable of delivering any measurable increase of accuracy if it did, and (2) about the same percentage of shooters lack the shooting skills to demonstrate any improvement if they had a rifle that would. The time wasted could better be spent on factors that actually improve accuracy. Many of which tend to be ignored.

 

[cfullgraf]

I'll agree that for most folks and most shooting activities, sorting case weights is not necessary.

But, about 12 years ago, I did a similar case weight study for 223 Remington as Bart referenced in Post #13 only I did fewer case stamps and sample sizes were much larger. My results were similar to 6mmbr.com's study. One note though, I found some cases in a sample whose weights were outside +/- 2 standard deviations and a couple outside of +/-3 standard deviations.

So, where shots count, the studies indicate why one might want to use one case head brand. Also, from what I learned, it is also not a bad idea to check for outliers from the lot. A simple, low effort activity that will minimize the chance of a flier.

Also, the information and knowledge gleaned by the top competitive shooters and long range shooters is always good to know. It gives the average shooter the basis to decide where to spend his time to improve his shooting.

I have participated in enough competitive activities, both inside and outside of shooting, to know that equipment limitations can hamper even the novice competitor. Of course, the almighty dollar gets in the way at times as well.

Hey Bart, thanks for the information.

 

[Bart B.]

With all case weights and/or volume equal, bullet velocity spread can be low. But there's one other variable that causes horizontal shot stringing with those cases; a half MOA or more is observed in very accurate rifles.

Case wall thickness ain't always uniform. It can vary a few thousandths inch. Pressure pushes the thin wall side further out than the thick wall side. Compare opposites of this once-fired case at its pressure ring:



The thick side (left picture) shows no visible expansion; thin side has a visible step about 1/10th inch forward of the extractor groove where brass thickens into the case head. Cases with that step even in height all the way around have very uniform wall thickness. Typically all the way to the case mouth.

When fired, the thin side stretches more than the thick side. That makes case heads smack the bolt face off center because the case head is a little unsquare to the case axis. That causes the barrel to whip more in that direction. Bullets leave where the barrel points when they exit. Barrel whip axis this causes is typically at right angles to bolt lugs; they're at 6 and 12 o'clock in most bolt guns. Such cases in M1 and M14 match rifles string shots from 7 to 1 o'clock.

What do your fired cases look like?

Resizing such cases doesn't square up those out of square case heads. The problem is compounded if the bolt face ain't squared up to start with.