Just picked up some Lapua brass. I was wondering what was considered acceptable weight deviations. Weighed the brass and also filled some of the brass with water to see what the deviations were. If someone can tell me what the acceptable standards are I'd appreciate it. The weight variances of this brass is all over the map.
Acceptable weight deviations in brass.
- Thread starter onelastshot
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Ned Ludd
Silver $$ Contributor
The density of brass is a little over 8 times greater than water. Assuming that case weight variance perfectly corresponds to case volume variance (in actuality, it doesn't), how much case volume variance would your case weight variance translate to? Just divide the case weight variance by 8. If it's less than 0.1 to 0.2 gr calculated volume variance, it might not be worth worrying about. If it's greater than that, you can sort cases by weight or volume (better) into smaller individual groups that each have less total variance within the group.
Shynloco
You can lead a horse to water, but ........
I cannot address this issue as technically as gstaylorg did. But I will say this, I weight all my brass in its final prepared stage for reloading, load them and then shoot them in weight order of the fully loaded cartridge. I've generally found that with Lapua brass, the fully prepped by unloaded cases vary as little as .03gr and as high as 1 gr. Therefore I shoot them in groups weighing as close as possible. Just my .02 worth.
Alex
Alex
I weigh sort my lapua brass. Just sorted a batch of fired brass i ultrasonic cleaned,.neck turned, annealed and trimmed. Put together a group of of cases that varied by less than half a grain. This weekend the target will tell the tale. Only thing i don't like is i have removed all the carbon from the necks. I will lube them up with imperial dry neck lube but my experience is these cases will do much better once they have been shot a few times and that carbon is replaced
ronemus
Gold $$ Contributor
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.
You are a victim of your own ability to weigh.
Your ability to weigh with a quality scale easily exceeds the 6 sigma limits of the case manufacturing process. Just because you can weigh cases to .001 gram does not mean the manufacturing process can produce them to that standard 100% of the time. You could weigh all of your brass and calculate the 6 sigma limits of the process and use only the the middle 2 or 4 sigma cases for competition. In other words what is acceptable is what you are willing to afford. If you want better weights buy a butt load of brass and sort it all to some milligram standard and put it in to bin lots for use. If you do not like the brass you are buying, then buy another brand so that you may find out if you like it even less. All brass is going to have weight variation due to the manufacturing process. The only way to get brass that all weighs the same is to buy about 20X the amount of brass that you need and sort it.
Otherwise brass is 8X heavier than water and powder. Determine what powder charge variation you can stand. Then convert that into the same variation in brass weight which is 8X heavier. You can also work up your own logic. In other words determine what is acceptable to you. But I can guarantee you one thing, since brass is 8X as dense as gun powder .1 grain of gun powder is NOT equivalent to .1 grain of brass.
For more reading material look up 6 sigma limits for statistical process control.
Your ability to weigh with a quality scale easily exceeds the 6 sigma limits of the case manufacturing process. Just because you can weigh cases to .001 gram does not mean the manufacturing process can produce them to that standard 100% of the time. You could weigh all of your brass and calculate the 6 sigma limits of the process and use only the the middle 2 or 4 sigma cases for competition. In other words what is acceptable is what you are willing to afford. If you want better weights buy a butt load of brass and sort it all to some milligram standard and put it in to bin lots for use. If you do not like the brass you are buying, then buy another brand so that you may find out if you like it even less. All brass is going to have weight variation due to the manufacturing process. The only way to get brass that all weighs the same is to buy about 20X the amount of brass that you need and sort it.
Otherwise brass is 8X heavier than water and powder. Determine what powder charge variation you can stand. Then convert that into the same variation in brass weight which is 8X heavier. You can also work up your own logic. In other words determine what is acceptable to you. But I can guarantee you one thing, since brass is 8X as dense as gun powder .1 grain of gun powder is NOT equivalent to .1 grain of brass.
For more reading material look up 6 sigma limits for statistical process control.
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I never enjoyed sorting cases by volume of water, so I stopped. Now I just weight sort after prep is complete, it is fired, resized and trimmed. Depends on the brass, but usually sort by 1/2 gr. and pull the outliers. I end up with a Bell Curve on the bench. I pick the middle, usually 75-90% of remaining cases.
My next step is a 2nd firing with proven load and seating depth at 200 yds in good conditions. Any case that throws a round out of moa, barring shooter error, gets pulled.
Last test is at 4-600 yds, same criteria. By then, I have only have 50-60% of original lot remaining. Over time, there will be a few more go in the fouler box, but I end up with a reliable lot of long range brass.
Like ireload2 said, buy a butt load of brass. Gets more expensive with bullets, powder and barrel life.
My next step is a 2nd firing with proven load and seating depth at 200 yds in good conditions. Any case that throws a round out of moa, barring shooter error, gets pulled.
Last test is at 4-600 yds, same criteria. By then, I have only have 50-60% of original lot remaining. Over time, there will be a few more go in the fouler box, but I end up with a reliable lot of long range brass.
Like ireload2 said, buy a butt load of brass. Gets more expensive with bullets, powder and barrel life.
For Practice ammo.....
Brass weighing around 90 gr (like 223r) I like 1 gr variation but 1.5gr is acceptable.
Brass weighing 160-170 gr I like 2 grains ES, 2.5gr ES is acceptable
Brass weighing about 250 gr I accept up to 3 gr ES but 2.5 ES is ideal.
For Serious shooting I sort by weight... The Extremes (lightest and heaviest) get used for fouling.
Brass weighing around 90 gr (like 223r) I like 1 gr variation but 1.5gr is acceptable.
Brass weighing 160-170 gr I like 2 grains ES, 2.5gr ES is acceptable
Brass weighing about 250 gr I accept up to 3 gr ES but 2.5 ES is ideal.
For Serious shooting I sort by weight... The Extremes (lightest and heaviest) get used for fouling.
Weight means nothing. The internal case volume is what matters. Many of times I have seen one full gran difference and the internal volume be the same . Larry
OKAY, I think most shooters know case weight does not track accurately with case volume. That is a given. So what volume discrepancy is preferred?
Also, I have heard that sorting cases by capacity of a ball powder will give accurate volume data. I know water volume is the preferred method. Just wondering if anyone uses the ball powder method.
Also, I have heard that sorting cases by capacity of a ball powder will give accurate volume data. I know water volume is the preferred method. Just wondering if anyone uses the ball powder method.
Unless you are willing to measure the volume of every case, volume is not of much value.
Since cases spring back varying amounts even case volume is not absolute either.
BTW weighing powder is not all that precise either because weight is not an exact predictor of the surface area of the propellant when it is ignited.
Since cases spring back varying amounts even case volume is not absolute either.
BTW weighing powder is not all that precise either because weight is not an exact predictor of the surface area of the propellant when it is ignited.
I have
i have didn't work for me . Filed the case and wiped it off then used a long drop tube and was far different . Larry
I would expect the throw or pour would have to be consistent, very consistent.
ireload2,
I guess we're just a dog chasing our tails. LOL
I thought it was great then I tried the drop tube . With new powder ever time I changed the way I did it .I got a different fill weight
Water is the best . I made a tool that fills part of the neck and the volume is always off the shoulder . Repeats 10 times . Larry
Jesus has spoken, weight means nothing! By the way, what is a gran? It's not a measurement I'm familiar with.
Must mean a lot thanks for the compliment
You can weigh your cases I will continue doing internal volume . lol Larry
Does sorting cases by weight or volume show on the target at 500 yds? Can anyone post some 3-5 shot groups using a ladder test with the only variable being the case?
Ben
Ben
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