Case weight uniformity

[Dcaven]

I am trying to load for precision. I shoot at 800 yards and would like to move to 1000 yards. My scope does not have sufficient magnification for 1000 yards so I am spending my time trying to work on better loading. Today I tried weighing my cartridge cases. They are not uniform at all. I can't remember how much they vary but it is several grains. How uniform should they be for best results? If the necks are turned uniformly, the primer hole has been deburred and the primer pocket cleaned up, how much does case weight matter? I am using Winchester brass and they measure the correct length. No two cases measure the same weight so I don't really know what the criteria for sorting them would look like. Thanks for your help.

David

 

[Sheldon N]

Did you have a chance to read this thread?

http://forum.accurateshooter.com/threads/sorting-cases-by-weight.3898477/

 

[Dcaven]

Did you have a chance to read this thread?

http://forum.accurateshooter.com/threads/sorting-cases-by-weight.3898477/

I did but have to admit it didn't all make sense to me. I'm learning as I go. Many contributors to that thread had very different ideas. I'm not sure whether I should focus on case prep and making those changes be as uniform as possible or if I should start with weighing each case. If I weigh cases, I'm not sure what the acceptable variation should be. I think someone wrote 1 grain. Mine differ enough I could never reach that standard. I'm looking for a place to start. I have so much Winchester brass that switching to Nosler brass is not really an option. By the way, I am not starting with new brass.

 

[ireload2]

In the end this is going to be an economic decision.
Weigh all of your cases. Using Excel put your cases in .5 grain bins and graph the data.
You should get a normal distribution. (check an introductory statistics text)
You will be able to see the cases in the left tail that are much lighter and those the right tail that are heavier.
Decide what cases you can or should live without and quit using them.
To help compare brass weight and its affect on the powder volume just remember that brass is about 8X more dense than powder.
If you can live with a plus or minus .2 grain powder charge you should be able to live with a plus or minus 1.6 grain case since the two variations would take up the same space in the powder chamber.

I did but have to admit it didn't all make sense to me. I'm learning as I go. Many contributors to that thread had very different ideas. I'm not sure whether I should focus on case prep and making those changes be as uniform as possible or if I should start with weighing each case. If I weigh cases, I'm not sure what the acceptable variation should be. I think someone wrote 1 grain. Mine differ enough I could never reach that standard. I'm looking for a place to start. I have so much Winchester brass that switching to Nosler brass is not really an option.

 

[Marksman63]

Case's volume uniformity is the key but, unfortunately, cases' weight is not correlated to their volumes

 

[ireload2]

If you put X number grains of brass in the chamber there is going to be Y volume of brass in it - guaranteed.

Case's volume uniformity is the key but, unfortunately, cases' weight is not correlated to their volumes

 

[Bronsin]

What you are really looking for is internal case volume, so why not measure just that? Take your fired cases with the primer still in, and fill each case with Ball powder and level it off with a knife. Then just weigh the amount of powder the case holds.

I did this with my .223 cases, and found that for every .3grs the case changed, was the same as a .1gr difference in powder capacity. It may not be the same for yours depending on the cartridge you are using, but you will still be able to find the answers you're looking for.

 

[Shynloco]

David,
For what it's worth, in my experiences with testing and comparing brass for consistency and accuracy (in several calibers), Winchester is amongst the LEAST consistent I've found in both weight and internal case volume. I and many others use Lapua brass because it has proven over the years to be the MOST consistent in those categories. There are others that rank ahead of Winchester as well. I know if I were competing, I'd spend the extra money for the "good stuff" and use the Winchester for foulers.

Alex

 

[Mozella]

....... snip...........
To help compare brass weight and its affect on the powder volume just remember that brass is about 8X more dense than powder.
If you can live with a plus or minus .2 grain powder charge you should be able to live with a plus or minus 1.6 grain case since the two variations would take up the same space in the powder chamber.

This makes no sense to me. The question at hand is: Does weight sorting (easy) serve as a reasonable substitute for volume measuring (tedious)?

A loaded case is filled with a combination of powder, air, and (partially) the base of the bullet. With closely controlled seating depth and powder charge weight, the remaining variable is the amount of air because, it is assumed for purposes of this thread, one case will have a different internal volume than another.

The argument rages on about how much case weight correlates to case volume. Some say not at all, others disagree. But I think most people agree that cases do vary in volume. I think most people will also agree that empty space in a cartridge (assuming constant seating depth and charge weight) will have an effect on chamber/barrel pressure; the idea being that if you can hold that empty space constant by sorting your cases or buying better quality brass then you will enjoy improved consistency at the target.

Both errors in powder charge weight and differences in empty space inside a loaded case will effect chamber/barrel pressure, burn rate, and barrel time and; therefore, will have an effect on precision at the target. I'm sure there is a relationship between these two possible reloading variances. But, even if case weight differences properly describe variations in case volume, I would argue the ratio of the density of brass vs the density of powder does not properly describe the relationship of charge error vs differences in empty space inside a loaded cartridge when it comes to group size on the target.

Said another way: Variations in weight and volume of brass, air, and powder certainly have an effect on precision but the ratios of these variables isn't linear. Consequently, I don't believe you can say an error in charge weight will produce a change in POI similar to a variation in case weight which is eight times as large as the charge weight error.

 

[ireload2]

No that was not the OPs question> >>> No two cases measure the same weight so I don't really know what the criteria for sorting them would look like.<<<<
What is the criteria? We are concerned about the effects of the change in volume.
So what is your criteria for filling the volume with powder? No tolerance or do you use plus or minus a grain or do you load it by volume from a measure?
If you allow the powder charge to vary you will also allow your cases to vary a little otherwise you will either have very few cases to use or you will have many small lots of case.
The brass changes the volume very little with one grain difference because the brass is 8X the density of most powders.
Try to understand that in sorting cases most of the intervals are going to be very small because of the density of brass. This is a way to grasp something that is very small and the .2 to .4 variations in case weight means essentially nothing because those variations represent very small deltas in volume. In other words 2 grains of powder is significant. Two grains of brass is not very significant unless the case is tiny.
At very small intervals the relationship approaches linearity.

This makes no sense to me. The question at hand is: Does weight sorting (easy) serve as a reasonable substitute for volume measuring (tedious)?

A loaded case is filled with a combination of powder, air, and (partially) the base of the bullet. With closely controlled seating depth and powder charge weight, the remaining variable is the amount of air because, it is assumed for purposes of this thread, one case will have a different internal volume than another.

The argument rages on about how much case weight correlates to case volume. Some say not at all, others disagree. But I think most people agree that cases do vary in volume. I think most people will also agree that empty space in a cartridge (assuming constant seating depth and charge weight) will have an effect on chamber/barrel pressure; the idea being that if you can hold that empty space constant by sorting your cases or buying better quality brass then you will enjoy improved consistency at the target.

Both errors in powder charge weight and differences in empty space inside a loaded case will effect chamber/barrel pressure, burn rate, and barrel time and; therefore, will have an effect on precision at the target. I'm sure there is a relationship between these two possible reloading variances. But, even if case weight differences properly describe variations in case volume, I would argue the ratio of the density of brass vs the density of powder does not properly describe the relationship of charge error vs differences in empty space inside a loaded cartridge when it comes to group size on the target.

Said another way: Variations in weight and volume of brass, air, and powder certainly have an effect on precision but the ratios of these variables isn't linear. Consequently, I don't believe you can say an error in charge weight will produce a change in POI similar to a variation in case weight which is eight times as large as the charge weight error.

 

[Sheldon N]

Here's some data on what the relationship between weight and volume looks like, Hornady brass, 284 Win.

 

[Mulligan]

Here's some data on what the relationship between weight and volume looks like, Hornady brass, 284 Win.

That speaks volumes!

I just opened a new box of Lapua 6BR brass and weighed them, all are within 1.8 grains.....pretty darn consistent and from the above information a complete waste of time. Time to fireform.
CW

 

[corning]

The question at hand is: Does weight sorting (easy) serve as a reasonable substitute for volume measuring (tedious)?

In my experience, for the same brand brass, yes.

 

[ronemus]

I did an experiment several years ago to determine just how much effect brass weight has on .223 loads. I used WW brass (sized, trimmed and deburred, primer pockets uniformed, flash holes deburred, and neck turned) , WSR primers, charges of RL-15 or N-550 powder weighed to 0.1 gr, and 75 gr A-Max bullets. Using the lightest and heaviest cases (sorted from 1000 once-fired I had on hand), I had two lots of 10 cases with a 3 gr difference in weight. The average muzzle velocity difference was 16 fps, just a bit more than the 12 fps due to 0.1 gr of powder. I choose to sort 0.5 gr lots of .223 brass for my long range loads, but the effect will only matter at 800-1000 yards - the vertical displacement on the target from such a small velocity change is negligible at shorter distances. Unless you control all other sources of variation, the effect of brass weight is negligible. I also shoot .284, and because the brass is twice as heavy I batch in 1 gr lots.

 

[chkunz]

I did an experiment several years ago to determine just how much effect brass weight has on .223 loads. I used WW brass (sized, trimmed and deburred, primer pockets uniformed, flash holes deburred, and neck turned) , WSR primers, charges of RL-15 or N-550 powder weighed to 0.1 gr, and 75 gr A-Max bullets. Using the lightest and heaviest cases (sorted from 1000 once-fired I had on hand), I had two lots of 10 cases with a 3 gr difference in weight. The average muzzle velocity difference was 16 fps, just a bit more than the 12 fps due to 0.1 gr of powder. I choose to sort 0.5 gr lots of .223 brass for my long range loads, but the effect will only matter at 800-1000 yards - the vertical displacement on the target from such a small velocity change is negligible at shorter distances. Unless you control all other sources of variation, the effect of brass weight is negligible. I also shoot .284, and because the brass is twice as heavy I batch in 1 gr lots.

Excellent response.

 

[Bell]

Excellent response.

ronemus...which cases produced the faster speeds, the lighter or heavier?

 

[ronemus]

ronemus...which cases produced the faster speeds, the lighter or heavier?

The heavier cases produce higher velocity for a constant charge weight; however a lighter case will let you add more powder and will ultimately produce higher velocity.

 

[Endyo]

...How uniform should they be for best results? If the necks are turned uniformly, the primer hole has been deburred and the primer pocket cleaned up, how much does case weight matter?...

David

Very little. There is very little correlation between brass weight and internal volume. Most of the weight difference is likely in the case web and some spread throughout the brass in variance in thickness.

Common knowledge states that a heavier case is thicker walled so there's less internal volume which creates higher pressure and higher velocity. It's a good theory but rarely backed with objective data.

What I thought mattered more was internal volume. Testing I performed with Sheldon N's help showed a weak correlation between internal volume and velocity and a basically very weak correlation between brass weight and velocity.

Neck turning on the other hand improved ES/SD by ~25-30%.

If it makes you feel better weighing brass do it! It's not going to hurt anything. For my sanity I've omitted it out of my process, there's a whole lot of other things to worry about and improve.

Edit: For other's who aren't in the OPs situation. If you're accuracy requirements are sub 1/4MOA it may be worth your time to weigh. YMMV. I've seen completely contradictory tests to mine.

 

[amlevin]

If it makes you feel better weighing brass do it! It's not going to hurt anything.

When I have a boring afternoon and need something to do other than watch TV, comb the cat, or re-read the newspaper, I will "weight sort" some freshly cleaned and prepped brass. The only benefit is that it's a great "time killer".