308 Winchester Case Capacities

[Reloadron]

During the course of another thread, the thread drifted off and around the original thread topic, we all know how that can go. The original post went as follows:
Is this over pressure?by Gobsmack

I fired a number of the following rounds of .308 and saw some cratering. Does it look like a problem? Details as follows: LC03 and LC05 brass trimmed to 2.005", headspaced to 1.625", CCI 34 primers, Hornady 168gr. BTHP, 41.6gr. of IMG4895. Hornady says 41.4 is max but QL says 44.9 is max and I see a ton of people using this 42-43 grains online. I actually went to 41.6 because I originally confused the H4895 and IMR4895 numbers BUT, QL insists that 41.6 should be fine.

Fired out of a Polytech M14S with a professionally and recently installed LRB bolt.

Plenty of good stuff was covered and a portion of the thread wandered into case capacities and involved the practice of reducing loads when loading standard military GI brass. The theory behind this thinking is military brass is heavier and thicker so logically if the outside dimensions are all made the same the thicker brass should result in less case volume inside the case. All very logical and makes sense.

I decided a small science experiment (as my wife calls them) was in order. I began with the basics, collecting what I hoped would be a wide range of brass. All of the brass was once fired, commercial and military. I selected ten cases each of Remington Peters, Winchester, WCC 10, LC 13 and Federal. That makes for 5 manufacturers including two GI brass in the lot. Each case was sized using RCBS sizing dies and case head to shoulder datum was set for 1.630" using an RCBS Precision Mic which I tested with a Forrester 1.630 Go gauge the idea being I wanted equal case dimensions case to case, The cases were all trimmed to a 2.005" case OAL.

Next I weighed all 50 cases with clean primer holes, the case insides also had a spinning brush used on them. Following weight I used tiny measured 1.5 grain balls of modeling clay to fill the primer pockets and flash holes. I mixed a few drops of Dawn dish washing liquid into a gallon of pure distilled water at room temperature of 70 Degrees F. I used an injector syringe to fill each case and then weighed the cases with water and subtracted the 1.8 grain tare for the modeling clay.

So now I know how much water each case holds and I converted that to Volume expressed as cc (cubic Centimeters) Becomes obvious that retired people. for the most part, have a surplus of time.

The cases were all dried and cleaned out. At this point my data sheet looks like this.




Looking at the numbers to date the RP Brass averaged 3.564 cc, the Winchester averaged 3.604 cc, the WCC 10 averaged 3.524 cc, the LC 13 averaged 3.541 cc and the Federal averaged 3.550 cc. So on average looking at the numbers the GI brass, the LC 10 and WCC 13 had lower averages than the three commercial manufacturer's brass. That being sort of expected. The nice number to look at though is The Standard Deviation number and this where small is good, like a golf score, the lower that standard deviation the more uniform the cases actually are and hand loaders should like that uniformity. This is where part 1 of my little science experiment ended for the year. So while the numbers change, how much will that volume metered change effect the powder charges and pressure?

My goal here is to prime each case with a CCI #200 large rifle primer and charge each case with 41 grains of AA 2495 powder under Sierra Match King 168 grain bullets using an RCBS micrometer bullet seater so all 50 bullets are seated uniform, or as close as I can get. Each 10 shot group will be run over an Oehler 35P Chronograph. I also hope to instrument the gun with a strain gauge pressure sensor so I can record the pressure curves. Granted I will not capture dead accurate pressures but I am more interested in just plotting curves for each shot. The latter will take some work but it should be a warm nice summer. I will also record the ammunition temperatures. This is more about curiosity than much else. Looking at the numbers in the spread sheet how much difference will those case volumes change for a given load and bullet weight> Rhe real question becomes will it matter enough the change velocity 15 feet downrange of the muzzle? Will it change things to actuallt see a pressure curve change? How much, in this scnario, will it matter?

I am very open to any thoughts or ideas.

Ron

[USSR]

Ron,

Sounds like a nice summer project for a retired guy with free time on his hands. Looking forward to your results.

Don

[hagar]

Weigh a LC case, and then weigh a WW case. You'd be surprised at the difference. The WW case can take more pressure because of higher capacity, the LC case can take more abuse from autoloaders.

[Reloadron]

hagar:

Weigh a LC case, and then weigh a WW case. You'd be surprised at the difference. The WW case can take more pressure because of higher capacity, the LC case can take more abuse from autoloaders.

Uh, I did that. On the above spreadsheet I weighed 10 each of Winchester and Lake City 13 cases. The average weight for the Win cases was 164.4 grains and the average weight for the LC 13 cases was 178.8. On average the LC 13 cases were 14.4 grains heavier. The average volume for the Win cases was 3.604 cc and the average volume for the LC 13 cases was 3.541 cc. The difference between the two averages to be 0.063 cc of case volume with the lesser volume going to the LC cases which was pretty much expected.

When a case is fired in a rifle's chamber the case will expand to fill the chamber and conform to the chamber. How much the case expands should be a matter of chamber size more than anything else. So how do we figure the Win case can take more pressure? Both cases will expand and conform to the chamber. The case with the lesser volume will generate the higher pressure for the same load and bullet seating depth and weight. The question is with the small difference in volume how much will it matter?

Ron

[F. Guffey]

During the course of another thread, the thread drifted off and around the original thread topic, we all know how that can go.

I am very open to any thoughts or ideas.

I suggested the primer was a reverse of the firing pin and firing pin hole. And then there are push feed ejectors that are outies and there are some that are inies . On the outies that are protruding there can be an imprint on the case head caused by the small .7854 case head support but most will say it is caused by high pressure.

F. Guffey

[Reloadron]

Mr. Guffey, can we just stay focused on case capacity. That's why I referenced case capacity in the thread title. Yes, I have seen the symptom you describe and no I do not just assume the cause as high pressure. That said can we just focus on the thread title?

Thanks
Ron

[308Loader]

Very interested in your results Ron. I've read many derailed posts on the subject with no clear answers or properly derived conclusions. When you plan to choot-em?

Cant wait until I retire, only 20 more years! That is of course if the job doesn't kill me first.

[Unclenick]

These numbers have changed over time. When Winchester designed the brass for the 1992 International Palma match, they initiated use of ther semi-balloon head case design that a lot of their rifle brass has now, but their goal was maximum powder capacity. IIRC, they weighed in at 150 grains and could take about 2 grains more poweder than a military case. But they weren't concerned about reloading life as the International Palma rules back then required the Palma host country to supply the ammunition used, so they mainly just needed to get one firing out of them. I do recall around two or three years later seeing the fired 92 Palma headstamp cases for sale on Commercial Row at Perry by the thousands. Wish I'd had the money to lay in some then, even if they weren't destined to last long.

A lot of Winchester cases I bought in 2005 had an average weight of 156 grains, so they had thickened up a bit by then, but the spread was bad. The lightest was about 152.5 grains and the heaviest was about 159.5 grains. I discerned four different bell curve peaks and concluded I had cases off four sets of tooling.

To keep peak pressure constant, figure about 0.6 to 0.7 grains of powder per grain of difference in case capacity, with small differences between brands. Constant velocity will run closer to the smaller number.

I don't know why the numbers have tightened. I can tell you that about 7 grains of empty weight difference can occur with no change in case capacity just by taking the head through the full cumulative range of the SAAMI standard tolerances for the head as to widths and extractor groove relief angle and so on, while keeping the internal head height constant and also using the full range of densities of brass alloys the different manufacturers employ. I can tell you that in 2012, ATK moved Lake City standards to match Commercial ones more closely in order that more ammunition suppliers would be eligible to make military spec ammunition during a wartime shortfall.

[FrankenMauser]

Edit: Unclenick posted while I was typing, and also contradicts my own experience.
Perhaps Winchester just switches it up out of boredom every few years...
My unchanged post remains below:


I find your Win and WCC results to be especially interesting. Most of the WCC brass that I have measured is pre-1993 and has a 54.0 gr H2O capacity, while most of the Win is fairly new and has a 58.0 gr H2O capacity. (With case weight also differing accordingly.)
At some point, they thinned the case walls. ...But perhaps not with ALL sets of tooling.


Although not a factor for much discussion in this thread, I deal with the same thing with .307 Winchester. Winchester originally drew the cases with thicker walls, falling into that 54 gr H2O class (which matches their old WCC "NATO" brass). But at some point in the '90s or early 2000s (probably when it was necessary to have some new draw dies made), they got cheap and thinned the walls to what they were using for standard '.308' brass. As a result, there's old Win at 54 gr H2O, new Win at 58 gr H2O, Hornady at 55 gr H2O, Jamison at 57 gr H2O**, and, soon, Starline at an as-yet-unknown capacity (but likely on the lower end).

**Measured and reported by others. I have avoided the Jamison, simply to reduce the number of different case capacities that I have to deal with.

[Reloadron]

As to getting this brass loaded I should have range results around the end of June as my wife and I have several things going right now. More things than I would like. I really would like to be able to plot some pressure curves and as I mentioned, not so much for actual pressure but just to get a good look at the actual curves.

Brass will vary lot to lot and even within a lot. A big problem focuses on Unclenick's and FrankenMauser's post. The Remington brass I used for this was New Brass 23 years ago when I fired it. It was once fired and has laid in a plastic ammo box ever since. The Winchester brass I really have no idea as I randomly yanked ten out of a one gallon ziploc bag. The military brass at least carries a year stamp but short of going out and buying some new I really can't date. The same is true of the Federal. The Federal was in a box of Federal Gold Medal Match which looks to have a lot #715235R176 and I have no clue when I shot the stuff let alone bought it.

All I can do is look at what I have. What is interesting and I am curious about is how much difference some of the case volumes will really have.

Many thanks to those tossing more info in and for posting to the thread.
Ron

[RC20]

Weigh a LC case, and then weigh a WW case. You'd be surprised at the difference. The WW case can take more pressure because of higher capacity, the LC case can take more abuse from autoloaders.

Hmmm, more grains of powder and a WW can take more pressure? I don't think so.

I did a test a while back. Being the simple sort of guy I am I did a simple test.

I took the range of 308 cases I had, all with fired primers, then I put in as much fine grain (748 I think) and smothed the top and weight the power.

As I recall the ratio was that it took about 5 grains of case eight to have 1 grain of powder difference.

[Howland]

Now I don't feel too bad. I bought a case of 1,000 IMI Match .308 brass and weighed them. Average weight was 179.971 grains which puts them right in the ballpark of LC brass and standard deviation was 0.698 grains.

I can't complain, 29¢ each and the flash holes look perfectly centered and as uniform in size as my eyes can tell and the neck anneal is uniform throughout the lot.

When I measured the headspace though, I was shocked to find the average was 0.0546" below SAAMI minimum. Then I took some unfired FGMM 168 and that was even less by one thousanth. I measured some once fired FGMM and it was closer by 0.015", so I guess I'll have to get to the fifth firing at least just to determine the chamber headspace and set my dies.

I'm glad I only have three .308s to load for.

[Reloadron]

"When I measured the headspace though, I was shocked to find the average was 0.0546" below SAAMI minimum. Then I took some unfired FGMM 168 and that was even less by one thousanth. I measured some once fired FGMM and it was closer by 0.015", so I guess I'll have to get to the fifth firing at least just to determine the chamber headspace and set my dies".

When doing this type of measurement much of what you get depends on the gauge used. Just as an example when looking at 308 Winchester cartridge and chamber measurements the minimum distance from case head to shoulder datum point is 1.630". Using a gauge like for example Hornady Lock-N-Load Headspace Gauge 5 Bushing Set with Comparator it was not really designed to provide a true indication of headspace. The one I have actually measures 0.006" low. Here is an example of what I am getting at:



When measuring an actual 308 Winchester headspace gauge measuring 1.630" my gauge reads 1.624".
[IMG]http://www.bearblain.com/images/CG4.png[/IMG]

The Hornady gauge was really designed so we could measure a fired case and then resize the case and note the change in case head to shoulder datum difference and it does that well. Again, keep this in mind when using a gauge like Hornady's.

Ron

[USSR]

For several years I processed .308/7.62x51, .30-06, and .30 Carbine brass coming off a range on Long Island for a guy with a Type 6 FFL (someone who can reload ammo and sell it), so I saw all kinds of commercial .308 and military 7.62x51 brass. Winchester was always the lightest weight and had a slightly higher case capacity. Even when looking at only military 7.62x51 brass, WCC was lighter than LC or RA brass or any of the foreign manufacturers brass.

Don

[Reloadron]

RC20:

Hmmm, more grains of powder and a WW can take more pressure? I don't think so.

I did a test a while back. Being the simple sort of guy I am I did a simple test.

I took the range of 308 cases I had, all with fired primers, then I put in as much fine grain (748 I think) and smothed the top and weight the power.

As I recall the ratio was that it took about 5 grains of case eight to have 1 grain of powder difference.

Another good way to go. When the VMD (Volume Measured Density) of powder we can fill a case with powder then weigh it. The convenience of using pure water is 1.0 cc of water = 1 gram of weight which = 15.432 grains of weight. This white paper covers it pretty well. The VMD of Win 231 should be about 0.0931 and Win 748 is about 0.0655.

Ron

[Reloadron]

Don,

For several years I processed .308/7.62x51, .30-06, and .30 Carbine brass coming off a range on Long Island for a guy with a Type 6 FFL (someone who can reload ammo and sell it), so I saw all kinds of commercial .308 and military 7.62x51 brass. Winchester was always the lightest weight and had a slightly higher case capacity. Even when looking at only military 7.62x51 brass, WCC was lighter than LC or RA brass or any of the foreign manufacturers brass.

Don

The brass I got from you was some of the finest I ever bought and Don has processed enough brass to be authoritative on the subject.

Ron

[F. Guffey]

Mr. Guffey, can we just stay focused on case capacity. That's why I referenced case capacity in the thread title.

I can; but I also consider the length of the powder column, the column can not be the same length if one case has a thick case head and another case has thin case head. And I also have to consider weight, if the case with the thin case head is the heavies I have to consider the possibility the heaviest case has to have a thick case body.

And there are some chambers that have a lot of case head protrusion. If I have not measured case head protrusion I want the case with the thickest case head.

F. Guffey

[F. Guffey]

The Hornady gauge was really designed so we could measure a fired case and then resize the case and note the change in case head to shoulder datum difference and it does that well. Again, keep this in mind when using a gauge like Hornady's.

The Hornady/Sinclair tool started out as a comparator and then reloaders started renaming tools, it was about that time ever tool became a head space tool and everything had head space.

From the beginning I claimed the datum based tool had to have a sharp edged datum; a tool with a radius on the edge of the datum was not accurate. And then there is an exception. The exception is the L.E. Wilson case gage; the Wilson case gage has datum with a radius. They build the tool with the datum with a radius and then grind the tool to length.

F. Guffey

[Howland]

Originally Posted by Reloadron

When doing this type of measurement much of what you get depends on the gauge used. Just as an example when looking at 308 Winchester cartridge and chamber measurements the minimum distance from case head to shoulder datum point is 1.630". Using a gauge like for example Hornady Lock-N-Load Headspace Gauge 5 Bushing Set with Comparator it was not really designed to provide a true indication of headspace. The one I have actually measures 0.006" low. Here is an example of what I am getting at:



When measuring an actual 308 Winchester headspace gauge measuring 1.630" my gauge reads 1.624".
[IMG]http://www.bearblain.com/images/CG4.png[/IMG]

The Hornady gauge was really designed so we could measure a fired case and then resize the case and note the change in case head to shoulder datum difference and it does that well. Again, keep this in mind when using a gauge like Hornady's.

Ron

Ron,

Exactly the tool I used (except I must subtract instead of zeroing) and I get why they call it a comparator instead of a gage.

The points were two; 1.) my observation of uniformity of the lot, but primarily 2.) weight alone won't correlate to case capacity unless all dimensions are equal.

Until shoulder expansion reaches the chamber shoulder and is then uniformly resized, I won't gain or lose mass. Even running new brass through a FLD won't get you to where case capacity has meaning. It's a dimension that must be uniformed before case capacity is relevant.

[Reloadron]

Absolutely, I agree with that. The objective of doing little science experiments like this at the range and kitchen table is merely to gather data to reinforce what we for the most part already know.

Something I have always been curious about, looking at the numbers I posted, how much will it matter? We know that for a given load in less volume the generated pressure will be higher. Now with that in mind how great will the pressure difference matter? I don't have Quick Load which would use a software solution and if anyone who does would like to run the numbers please feel free.

So I agree absolutely with what you covered.

Thanks
Ron

[RC20]

Ok, I not only use the Hornady, but being the cheap bugger I am, I didn't buy the case shoulder set to go with it.

I made one of my own from the spare bullet ogive set. And yes as long as the bullet/neck is not too long it works.

So, it makes zero difference what the accumulated error is.

Going from memory, I get say 1.638 on a fired case.

I then work the dies until it sets back to 1.366 or 1.367.

It matches no one elses measurements, its a unique setup. I now the gun head-space (or I can let the grow grow until it is) is fine, all I need to do is bump it back .001 or .002.

Works just fine. The bullet adapter was just drilled out to hit the Ogive on a 30 caliber bullet. Did the same on 270.

[Reloadron]

Mr. Guffy

The Hornady/Sinclair tool started out as a comparator and then reloaders started renaming tools, it was about that time ever tool became a head space tool and everything had head space.

From the beginning I claimed the datum based tool had to have a sharp edged datum; a tool with a radius on the edge of the datum was not accurate. And then there is an exception. The exception is the L.E. Wilson case gage; the Wilson case gage has datum with a radius. They build the tool with the datum with a radius and then grind the tool to length.

F. Guffey

The Hornady Tool is till a comparator. I believe that has been covered in a dozen plus threads. Reloaders did not start renaming tools, the guys making and marketing the tool decided what to call it. I am sorry they did not consult with you but I should point out they also did not consult with me. Now I figure there is nothing I or even you can do about their naming conventions. I guess if you were manufacturing gauges or tools you could call them or name them whatever you wanted to. You may wish to write them a letter voicing your displeasure and I wish you good luck on that.

Now can we just focus on case capacity and for example in the data I posted what would the effect be on chamber pressure for the same loads?

Thank You
Ron

[FrankenMauser]

Something I have always been curious about, looking at the numbers I posted, how much will it matter? We know that for a given load in less volume the generated pressure will be higher. Now with that in mind how great will the pressure difference matter? I don't have Quick Load which would use a software solution and if anyone who does would like to run the numbers please feel free.

I've run the numbers through QL many times for .307 Win. Basically the same case capacity, similar bullets, just running lower pressure.
A 160 gr FTX load worked up in my 58.0 gr H2O capacity brass and running at 52k psi (SAAMI MAP) with CFE 223 jumps to more than 63k psi if put into 54.0 gr H2O brass.

The powder being used can have some impact on pressure increasing more dramatically, but the numbers are similar with .308 Win.
Running the same 160 gr FTX over Varget at SAAMI MAP of 62k psi in 55.9 gr H2O capacity brass, for example, will jump to over 69k psi in 53.8 gr H2O brass.
Oh... I forgot to note the velocity differences. I didn't record the actual predictions, but the difference is around 80 to 120 fps different with most powder/bullet combinations from a 20" barrel. (I was set for my 20" .307 and didn't think to change it while running the numbers for .308.)

As always...
Keep in mind that while QL is an exceptionally well-tuned program for cartridges like this, and the powder database is built with actual pressure testing, it is still just a simulation. Real world numbers would probably be close, but not the same.

[Reloadron]

RC20:

Ok, I not only use the Hornady, but being the cheap bugger I am, I didn't buy the case shoulder set to go with it.

I made one of my own from the spare bullet ogive set. And yes as long as the bullet/neck is not too long it works.

So, it makes zero difference what the accumulated error is.

Going from memory, I get say 1.638 on a fired case.

I then work the dies until it sets back to 1.366 or 1.367.

It matches no one elses measurements, its a unique setup. I now the gun head-space (or I can let the grow grow until it is) is fine, all I need to do is bump it back .001 or .002.

Works just fine. The bullet adapter was just drilled out to hit the Ogive on a 30 caliber bullet. Did the same on 270.

While I love being retired something I really miss is in my little skunk works we had a really sweet machine shop where we did prototype work. I was not a machinist or mechanical engineering type but had the pleasure of working with some of the best in the business. There were so many gauges I wanted to make before my last day and just never managed to get to.

I also use the Hornady and I like the RCBS Precision Mic gauges. The ones I have were bought many years ago and also were left over inventory. I just wish I still had that machine shop and lab at my disposal for side projects.

Ron

[Reloadron]

FrankenMauser, thanks for contributing that information.

As always...
Keep in mind that while QL is an exceptionally well-tuned program for cartridges like this, and the powder database is built with actual pressure testing, it is still just a simulation. Real world numbers would probably be close, but not the same.

Absolutely, it's a software solution based on their algorithm.

Ron