Velocity vs Brass Weight Experiment.

[Kmccord]

I am amazed you are getting the velocity with 180 gr bullet at 66.0 gr of H1000, I have a 7 Rem Mag I just finished load development using H1000 at 68.0 gr with 168 gr Berger HVLD and it is pushing it at 2830 FPS average, my rifle only has 110 rounds down the tube and it is a 24" barrel.

 

[Jpron]

I've seen the exact same thing with cheaper brass, Winchester, Remington, hornady. When using nosler or adg, not so much. But the difference in weight between brass in the higher priced brass is way less. When loading with cheap brass I definitely sort them out.

 

[entoptics]

I am amazed you are getting the velocity with 180 gr bullet at 66.0 gr of H1000, I have a 7 Rem Mag I just finished load development using H1000 at 68.0 gr with 168 gr Berger HVLD and it is pushing it at 2830 FPS average, my rifle only has 110 rounds down the tube and it is a 24" barrel.

Mine is a 26" X-Caliber, 1:8, 5R. Based on what I've seen published, and anecdotal reports, I don't think 66 gr is very salty. I didn't notice any pressure signs until I got up to 69.5 with the ELDX.

I shot about 75 rounds through the OEM barrel (used rifle so I don't know total round count) before I took it off. It was actually about the same speed, though it is 2" shorter at 24". I had very similar pressure signs with it (i.e. no signs till ~69 gr).

Perhaps you just have a slow barrel, or H1000 isn't quite as efficient for the lower weight bullets?

 

[DNADave]

Looking at the OP's graph, weight of brass explains just over 22% of the variance in velocity he observed (that's an interpretation from the R^2 number below the line in his graph). This means that just over 77% of the variance in velocity was explained by something he didn't measure. That model is not a great fit to the data and something else is the primary driver of velocity (although brass weight does explain at least some of the variability).

I saw someone else mentioned case capacity versus weight. Given that there is a weak relationship between brass weight and velocity, I could see where using capacity might fit the data better. Only one way to tell and that is to measure the brass capacity, load, and then measure the velocity again.

And yes, I am a nerd and a card carrying statistician (secretary of the Puget Sound American Statistical Association and a Fellow of the Royal Statistical Society).

 

[entoptics]

Looking at the OP's graph, weight of brass explains just over 22% of the variance in velocity he observed (that's an interpretation from the R^2 number below the line in his graph). This means that just over 77% of the variance in velocity was explained by something he didn't measure...

Wish I could figure out what that other 77% was...☹

The R2 on the averages graph is far more robust though, so I still believe there's significance in the correlation.

 

[Kmccord]

Mine is a 26" X-Caliber, 1:8, 5R. Based on what I've seen published, and anecdotal reports, I don't think 66 gr is very salty. I didn't notice any pressure signs until I got up to 69.5 with the ELDX.

I shot about 75 rounds through the OEM barrel (used rifle so I don't know total round count) before I took it off. It was actually about the same speed, though it is 2" shorter at 24". I had very similar pressure signs with it (i.e. no signs till ~69 gr).

Perhaps you just have a slow barrel, or H1000 isn't quite as efficient for the lower weight bullets?

Not sure on whether the powder is inefficient for that bullet weight, it was the most powder I have for the 7 mag. I never hit pressure, I went with the published data Berger gave me they listed 62.5 gr to 69.5, 68gr gave the best groups and repeated the same ES/SD 12 and 6. This is the Grandson graduation present, this load should work for him this season and see if it speeds up after 150 rounds down the barrel.

 

[cdherman]

Wish I could figure out what that other 77% was...☹

The R2 on the averages graph is far more robust though, so I still believe there's significance in the correlation.

I am not a great statistician, but I do dabble a lot in the field of medicine, and a LOT of what we do involves statistics. Any variable that might explain 23% of a disease or outcome is worth at least paying attention to. Especially, when a lot of the other 77% cannot be CONTROLLED or are unknown.

So, since weighing brass is CONTROLLABLE, why not do it? I weight my brass, throw out or mark for foulers a few.

Try to narrow the spread to around 1% of average case weight. Why 1%? Cause I read that somewhere and it seems a decent place to start. It also results in very few culls in quality brass (Laupua, etc). Also, since a given volume of brass is a lot heavier than water or powder, variations in brass weight equate to case capacity volumes around 1:7. So a 0.7 grain change in brass volume is roughly like adding 0.1 grain powder capacity. Ergo, for a case that weights say, 180 grains (like my Nosler 270 brass), a 1% variation in weight would be 1.8 grain brass, equivalent to 0.25 grain of powder. That's a pretty small amount of powder, and if your loads are that sensitive to charge weight, you are probably not in a good node.......

Lastly, several posts discuss some basic laws of physics: The volume inside your steel chambered rifle better not be a variable. I am telling you the obvious. If that number was changing in any appreciable degree, your gun would blow up. So, virgin brass aside, and resized brass aside, once brass has been fired once or a few times (brass does not always assume full expansion with the first firing, especially in lighter loads), and has reached "neck sized" dimensions, then the weight of the brass MUST have a direct correlation to the internal capacity of the case.

So, in other words, the correlation of weight of the brass to internal capacity, and thus behavior of the loads, depends a LOT on how many times the case has been fired, whether its being resized fully, and lastly, as noted by at least one post, the hardness of the brass (resizing a work hardened brass versus a soft new or annealed brass)......

Lots of variables. But if throwing away 5 brass out of a 100 eliminates a variable, why not?

Reloading is a science really. When you work up a load, you vary only one variable at a time, right? Only an idiot would load a set of loads and vary the powder charge and the depth of seating at the same time......

 

[Mikecr]

Weighing brass is EASY. Acting on that shortcut is where you'll be screwing up..
For all you'd know that 5 out of 100 would have performed with the mean, while some number of what you're comfortable keeping are actually worst in lot..
You would do better to sort as 25WSM was advised -by actual results per case.

 

[DNADave]

@cdherman the more I look at the original data, I wonder if this weak relationship between weight and velocity is due to two potentially influential points. The data point with the 2850fps and the data point with the 2930 fps seem a bit out of place and could be the reason we see a weak relationship. Without those two points, the regression line would be much more flat.

There are some tests that could be done to check their influence and potential to be outliers. I don't know if excel can calculate Press statistics, but that would give you the information you'd need to know if those points are outliers or not.

We're getting into serious nerddom, now... Can you tell I'm bored?

Edit: You can calculate Cook's D or DFFits using the formulas in this page: http://www.real-statistics.com/multiple-regression/outliers-and-influencers/

Both of those would be probably better measures to see if those two points are outliers. As @cdherman points out, the variation in weight in this brass is not really enough to cause large differences in velocity due to changes in volume that correlate with the weight in brass.

 

[DrDave]

It seem to me that small capacity cases like are more likely to demonstrate pressure and velocity differences based on case weights. I sort .223 cases by weight 1.5 grains. For example Lake City cases usually weigh around 5 grains less than USA or TAA headstands. The powder column is visibly higher in the heavier cases. There is a table in one of my reloading books that calculates amount to be decreased as case weight increased to have equivalent loading density. I load a lot of .223 and .20 Practical for prairie dog shooting and learned to sort my brass by weight to avoid over-pressure rounds. Empiric observation. I'm certainly no expert.

 

[Ingwe]

I have to give it to you fellas....the amount of knowledge on this website is mind blowing

the amount of time and effort that you guys put into this is incredible. I could never do it.
I don't have the head for it. I had my load developed for me and I know how to duplicate it on my equipment and tweak it if I change powder lots but that's about it. Good enough for hunting and dinging steel at 1,000 yards but I will never win a match lol

Keep up the great posts fellas, as I am learning allot here by readywgat you all have to say

 

[Mikecr]

There is a table in one of my reloading books that calculates amount to be decreased as case weight increased to have equivalent loading density.

PURE DELUSION
Case capacity (not case weight) affects load density.

If so willing to cull cases on weight alone, then you should be as willing to wait until fully forming and measuring results from each. Then you can actually feel good about tossing some. Then, you EARNED the knowledge.

 

[david g ranes]

PURE DELUSION
Case capacity (not case weight) affects load density.

If so willing to cull cases on weight alone, then you should be as willing to wait until fully forming and measuring results from each. Then you can actually feel good about tossing some. Then, you EARNED the knowledge.

An over abundance of case weight is going to create less volume in any given case the extra brass shut isn't on the outside of the case unless it's magic it must be taking up space on the inside when my Nosler brass weighed almost 60 grains difference between 5 year old lots it darn sure caused pressure problems whether it is to much or not enough. David

 

[DNADave]

I was thinking about this yesterday and the .223 might be the best venue to do an experiment. I have heard from several other posts in different threads that Brian Litz in his book mentions no gains in performance (accuracy or variation in speed, I don't know) from weight sorting brass. I haven't gotten that far in his book (my free version ended before that section I guess and I've only recently purchased the whole book), but I would assume he was using the .308 as his test case. Manufacturing tolerances are probably such that the percent change in volume due to variations in weight within a single manufacturer are so small as to be insignificant. Changes between manufacturers might approach or be significant. A .223, however, with its small case volume to begin with might have the level of correlation we would need between weight and volume to make a difference. We could perform an experiment (I'd be up for it, but I neither own a .223 nor can go to the range at the moment) and see what the difference is with weight as a percentage of volume. You could then extrapolate using the percentage that matters out to other cartridges based on their weight to see if even checking whether sorting would make a difference is worth checking there.

As @Mikecr points out, we are making an assumption that weight is directly correlated to volume which we know is not completely true, but there should at least be a weak relationship given that the outer dimension of the case is fixed at the chamber size. It just might take a small volume cartridge for that relationship to be strong enough to matter.