What's the big deal about weighing cases?

You are probably asking "Why should I weigh my brass and why should I even care?". Most handloaders have read about sorting cases by weight and some are somewhat confused about it. I mean, what can be simpler than a brass cartridge case? All it does is holds the powder, right? Actually, there is a little more to cases than that. Follow along and we will take a look at what I mean.

First off, let us look at what case sorting by weight is. This is a technique that is used to determine how consistent the brass of the case is. The closer the cases resemble each other the more consistent the results of the load will be. The reason is that brass of the same thickness and same length will give the same results each time if the same powder load, primer, and bullet is used. As we all know, one of the keys to accuracy is consistency.

Following the logic that the cases are made on the same machine and from the same sheet of brass we can determine the consistency of the cases by weighing them. If the case weight is too high or too low, it will likely have a case volume that is inconsistent with the others and produce less than acceptable performance. This is because thicker brass will be heavier, thus creating a smaller internal volume. This smaller volume will create higher pressure if all other aspects of the load are equal. Lighter cases will have a larger internal volume and produce less pressure.

Now that we know what weight sorting is and why it's done we will look at how it's done. The first thing we must do is get a scale that is accurate. Some loaders will use the same balance beam scale that they use to weigh powder. Others use an electronic scale such as those made by Lyman, RCBS, and PACT. I use an electronic labroratory balance that we have at work as it is super accurate and convenient. No matter the equipment used, you must verify it's accuracy with some sort of check weight. Once you are convinced of it's accuracy you can begin.

Obviously, we will need some cases for this. Choose whatever brand you want, the theory works the same. Most loaders will buy at least 100 cases to start with so we will work with that number.

Now that you have the cases, it is time to full length size them. Run them through the dies as you normally would. Once all are sized, clean them thoroughly to remove anything that may add to the weight. Trim the cases to the desired trim length, turn the necks now if you plan on doing it, and debur the flash hole. If you plan on doing anything else that will remove material from the cases, do it now.

Let's start weighing the cases. I like to take a random 25% sample of the cases to weigh for the standard. This is basically the average weight that we will use to compare the cases to. For this exercise, that will be 25 cases. Some loaders will weigh each and every case to produce their standard but those folks are the ones who generally don't have any friends.

We will take the standard that we just established and use to compare all of the cases to. I like to cull any cases that are not within 1% of the standard. For example, if the standard is 150gr, 1% is 1.5gr and I will cull all the cases that are more than 151.5gr and less than 148.5gr. When culling, place all the cases that are within the standard in their own pile, box or bag. Place all the cases that failed in the respective piles, one for lights and one for heavies. If there is a significant amount of either, you then weight sort those using the same method. This will allow these cases to possibly be used if they are kept seperated from the rest and labled.

Here are some examples of weight sorting using the 1% method:

Cartridge- .223 Remington; Brand- Lake City 02; Cases weighed- 25
High- 93.36gr
Low- 91.35gr
Avg- 92.18gr
Standard = Avg X 1% = 0 .92gr, acceptable range: 92.18gr +/- 0.921gr = 91.25gr to 93.10gr.
Found four cases that were too heavy and none that were too light.

Cartridge- .308 Winchester; Brand- Lapua; Cases weighed- 25
High- 173.61gr
Low- 171.19gr
Avg- 172.67gr
Std= 172.67 X 1%= 1.72gr, acceptable range: 170.95gr to 174.39gr
All cases were found to be acceptable.

Cartridge- .338 Winchester Magnum; Brand- Winchester; Cases weighed- 25
High- 236.88gr
Low- 234.15gr
Avg- 235.33gr
Std= 235.33gr X 1%= 2.35gr, acceptable range: 232.98gr to 237.68gr
All cases were found to be acceptable.

The above cases were weighed by me on an AND HR-120 electronic laboratory balance.

Many handloaders like to use the 1gr method of case weight sorting. They basically weigh all the cases and sort them into piles like in the above method. However, the standard that they use is 1 grain instead of 1%. The only problem I found with this method is that the rejection rate for small cases such as the .223 Remington is too small as practically all cases will be within 1 grain. The bigger cases experience a higher rejection rate because as the case gets bigger, the case weight naturally gets larger. Good cases get culled because they can't meet the 1 grain standard. The 1 grain standard is not a bad method by any means though and if you are getting good results from it, then by all means use it.