Nato Brass Case Capacity

[Randoman5]

I just bought a batch of what was advertised as fully processed once fired brass. Most of it is either 00s Lake City or TAA. I measured the overall length of the cases and found them to be fairly uniform by type and year with a variance that is all within the minimum and maximum ranges I see listed.

I'm somewhat concerned about the differences in case length, with some being only a few thousandths of within minimum length trimming to uniform length doesn't seem like a very appealing option. I'm sort of expecting them to stretch somewhat after I size them.

My bigger concern is case capacity. I know capacity will make a difference in pressure and velocity. I'm concerned that the brass will have such different volumes that doing a ladder test won't reflect pressures on subsequent reloadings.

I hear a lot about guys weighing cases, and right now I've only got the Lee safety scale, which doesn't have enough capacity.

The idea occurred to me to test and sort by volume by doing a water displacement test with a graduated cylinder in milliliters. The only thing I don't know is whether that will give me a fine enough measurement to make a difference.

Has anyone ever tried that?

 

[hdbiker1]

I just tare out a primed case and add water with a syringe until full and record the weight. Then I do the same with a Federal case, Lapua and Winchester or others. Remember that you have to fill to the same amount, ie. flush with the case mouth or same bubble height. Also, the cases should be the same length. I weigh the other cases because each manual will list what case their data is based on, and the Lapua because I use them for certain calibers. The more cases you weigh, the more accurate your numbers will be. Then I use those numbers in a proportional equation to adjust the load data. Maybe someone else will come along with a better explanation or better method.
Or you can use the trial and error method with a chrono to see what amount each case takes to obtain a certain speed.
It's late and I should be in bed.

 

[Mad_Charlie]

Evidently he doesn't have enough scale capacity.

 

[Randoman5]

Quick update. I remembered that water has a density of 1mg/ml and checked and found out 1mg = .015 grains. So if I assume that the exterior dimensions are the same, which they should be after sizing, differences in case volume determined using a water displacement method should equate to differences in case capacity measured in hundredths of a grain.

 

[bigedp51]

What caliber are you shooting?

 

[918v]

You should get an electronic scale they are cheap nowadays.

 

[dwkuska]

agreed and you can find em even at corner stores. The illicit industry of drugs has made digital scales cheap cheap cheap. You can TARE one with a nickle. If I remember right a nickel is 5 grams on the nose.

 

[bigedp51]

I asked "what caliber" because 7.62 cases tend to weigh more and have less cases capacity while the opposite is true of .223/5.56 cases.

Below are Quickload pressure and velocity charts, the top chart is a 5.56 Lake City case with the "MOST" case capacity and lightest weight. The bottom chart is for a case that weighs more and has "LESS" case capacity, both cases are loaded with the same charge of powder. If shooting mixed brass loaded with 25 grains of H335 the smallest capacity case will be well below max pressure.

Below a Lake City case with 30.6 grains of H2O case capacity. 44,000 psi

Below a generic case with 28.8 grains of H2O case capacity. (Quickload default) 50,000 psi

Below the Lake City case has the most case capacity, the case is also made to higher standards than commercial .223 cartridge cases.

Military cases are harder in the base than commercial cases because military chambers are larger in diameter and longer in headspace than commercial cartridge cases.

Milspec requirements for the 5.56 cartridge case.

 

[Randoman5]

These are .308 cases that will be fired out of a Remington 700 Varmint. My theory is that if the exterior of the cases are the same size after sizing than differences in the volume of the case must be due to wall thickness... although that may be too great an assumption to make.

If someone knew or had experience with case volume differences in different years and different manufacturers of NATO brass that would be helpful. My biggest worry is that if I do a ladder test with one group of brass and reach the upper limits of pressure, I'll load the same charge in a different cartridge and be over the limit. Secondarily I'm worried pressure differences will give me variation in velocity that cause misses at long range high or low or take me out of accuracy nodes.

 

[bigedp51]

The case capacity is to be checked with cases fired in your chamber and not resized. Quickload shows 52 grains H2O for the 7.62 and 56 grains H2O for the .308

Case Capacities

 

[rsplante]

Quick update. I remembered that water has a density of 1mg/ml and checked and found out 1mg = .015 grains. So if I assume that the exterior dimensions are the same, which they should be after sizing, differences in case volume determined using a water displacement method should equate to differences in case capacity measured in hundredths of a grain.

That's the way I see it. But in order for that to work, it goes without saying that you must not only be using the same brand of brass, but preferably also from the same lot of brass (or at least the same year.) Different manufacturers use different formulas for their brass and as a result the density changes. Also, I guess it is possible that some may have a different head thickness. I have been using 1000 LC11 cases and am on the third shooting cycle. I just upgraded to 1000 Lapua cases. I sort my brass in 0.1gn lots. With my GD503, I could sort to 0.005gn, but what's the use, out of a batch of 1000 cases, even with Lapua I would not get enough at the same weight to shoot a match. Now, if I had 10K or 100K Lapua cases, besides being broke, I would be able to sort to a more stringent standard.

 

[Randoman5]

I don't think my rifle is even capable of that level of accuracy. My only concern is that if there are big differences in case capacity will equate to pressure issues with loads tested with other brass. I tried to save some money on bass by buying once fired Lake City. We'll see if that ends up working or if I'd have been better off buying half the number of Lapua Brass for slightly more.

 

[OF&B]

Quick update. I remembered that water has a density of 1mg/ml and checked and found out 1mg = .015 grains. So if I assume that the exterior dimensions are the same, which they should be after sizing, differences in case volume determined using a water displacement method should equate to differences in case capacity measured in hundredths of a grain.

1 ml of water weighs 1 gram, 15.4 grains. This sorting goes pretty quickly with a digital scale.

Brass has a specific gravity of 8, meaning it takes 8 grains of brass to displace 1 grain of water.

My experience has been the relationship between case internal volume and case weight is breaking down by 1 grain of case weight on 223.

Sorting by head stamp and then into 2 grain lots goes pretty quickly and only has to be done once. If you're not trickling your charges, weight sorting brass probably isn't going to get you anything other than culls to use for setting things up and dummy cases.

My experience with Quickload and a chrono is the effective internal case volume is somewhere between the sized case volume and the unsized case volume plus the free bore.

 

[bigedp51]

I have three five gallon buckets of once fired .223/5.56 brass fired by our local police and SWAT teams. This brass is very frustrating even when sorted by headstamp and dates due to weight and case neck variations.

I use this brass for practice/blasting ammo in my AR15 carbine because it was made from lower grade brass and sold cheaply.

I have two AR15 rifles and a bolt action Savage with a 26 inch heavy barrel. After pulling my hair out with the three buckets of brass on an impulse I bought a box of Nosler custom brass. The Nosler brass comes weight sorted and the primer pockets and flash holes are already prepped. The uniformity and quality are worth the price without question, now buy some good brass from the same lot and save the Lake City brass for covering suppressive fire in Zombie attacks.

And use your best brass for head shots at long range. (Zombie case runout humor)

I'm retired with nothing to do and all day to do it, "BUT" life is to short to be sorting, weighing and checking H2O capacity of once fired mixed brass trying to find a few good cases.

Lapua cartridge cases
Products - Lapua

NoslerCustom® Brass
Brass ? Nosler

NOTE: Many competitive shooters buy Winchester brass from the same lots and then prep the brass for uniformity to save money. My Nosler cases were less than $20.00 more than winchester brass and all the prep work and weight sorting was already done. Meaning I got to spend more time shooting and less wasted time at the reloading bench.

 

[rsplante]

I don't think my rifle is even capable of that level of accuracy. My only concern is that if there are big differences in case capacity will equate to pressure issues with loads tested with other brass. I tried to save some money on bass by buying once fired Lake City. We'll see if that ends up working or if I'd have been better off buying half the number of Lapua Brass for slightly more.

I've been shooting 1000 LC11 cases for the past two years (half way through third use). I bought them as unfired. I then proceeded to spend several minutes on each case preparing them, and eventually I realized that the Lapua really isn't that expensive if you figure in your time and you want accuracy. With my LC brass, I full length sized them and trimmed the length. Chamfered inside and outside of neck. Skimmed the necks (compromise between saving as much neck thickness as possible and trying to even the thickness all the way around.) Trimmed the flash hole, normalized the primer pocket, sorted to .1gn.

I will still have to size and trim the Lapua, but since the flash holes are drilled instead of punched, I can skip trimming the flash hole. The primer pockets look pretty good, so I may skip normalizing them. One thing I have never proven, but highly suspect, is that my "one time" skimming of the necks on the LC may not suffice. If the brass is thicker on one side of the case than the other, as the case "grows" in length due to resizing (hence the need for trimming length), that brass has to come from somewhere. It is coming from the case body, so if it is uneven, that will propagate up into the neck. The Lapua brass is already within .0005" around the neck circumference http://www.sinclairintl.com/reloadi...r-starret-case-neck-micrometer-prod38096.aspx, so I will probably dispense with the neck skimming. I figure that conservatively I will save 1-2 minutes per case. That works out to ~1500 min, or 25 hours. 1000 Lapua cases cost $290 more than 1000 unfired Lake City cases. That means that if your time is worth more than $11.6/hr, and you want the utmost in accuracy, the Lapua can actually be cheaper than unfired Lake City brass. And that isn't even taking into account longer brass lifespan.

I expect them to last a lot longer (reducing the effective cost per round). I have started annealing New Page 1 my necks, which should greatly increase the useful life of my brass; however, that is only part of the story. The entire case is gradually thinning out, plus the primer pocket eventually gets loose. I am betting on the higher quality and thicker brass of the Lapua cases will handle that end. (The Lapua 5.56 cases weigh about 5gn more than the Lake City cases, or ~ 5.44% more.)

Finally, if you are not interested in super accuracy, it probably does not amount to a hill of beans. The density of brass is about 8520 kg/m**3. Out of a thousand Lake City 5.56 cases, the range of weights was 91gn to 93.1gn. That means a 2.1gn difference. There are 7000gn in a pound, so the difference in brass volume (since the outside dimension remains constant, the inside dimension is basically all that can change as you mentioned) over a batch of 1000 LC cases was .00097cu in, or .01589cc. I had planned on eventually checking case volume with water, and I think I just talked MYSELF out of it. There is no possible way that I will be able to measure .016cc which is the largest difference in my cases. I am currently segregating them by weight into 21 groups. That means I would have to be able to measure the volume of water to .00076cc just to equal what I am measuring by weight.