Velocity vs Brass Weight Experiment.

[entoptics]

Having some ES/SD issues with a 7mm Rem Mag, so I decided to run an experiment to see if brass weight could be the problem. I knew it was unlikely, but figured I should eliminate any possible variables (and COVID = what do I have better to do?). The results, though not perfectly well behaved, surprised me at least a little.

Summary for those who don't like nerd details...~1-3 fps per grain of brass. Weight sorting brass almost certainly can make a measurable difference, though it's highly unlikely to be the source of large ES/SD problems on average. I'd place brass weight pretty low on my list of "ways to improve ES/SD".

Nerd Details...

Brass Prep (not necessarily in this order, but close enough)
Remington brass, 2X fired, some not in this rifle, though all required FL sizing and shoulders bumped back.
SS Pin tumbled after universal decapping die.
Necks skim turned to ± 0.0005"
Salt Bath Annealed
RCBS Competition FL sized, no expander button, shoulder bumped to 0.002" ± 0.001"
0.283 Sinclair neck expander mandrel.
Trimmed to ± 0.001", chamfered, deburred
Flash holes chamfered
Primer pockets scrubbed (not really uniformed, though a little brass gets removed from the bottom making them a touch flatter)
Sorted by weight (± 0.1 gr)

Load
66.07 gr of H1000, weighed to less than a kernel (ES of 0.02 gr, SD of 0.007 gr)
180 gr ELD-M
Fed 215M primers
~0.02" off lands (± 0.001 BTO)
Powdered graphite applied to neck ID with q-tip after powder charged
4 shots each at 4 different brass weight "groups". ~227.5 gr, ~ 229 gr, ~230 gr, and ~233 gr. The lower and upper groups had wider spread, as I didn't have enough brass at the ends of bell curve to keep them tightly grouped.

Methodology
All shots were fired from prone, front rest, rear bag.
LabRadar acquired data for 80-150 yds for all shots, and raw data was checked in my regression spreadsheet to ensure no spurious readings.
Shots were fired "snake style" in 4 shot groups, with the rifle cooling for at least 10 minutes between each string to mitigate heating and fouling bias. i.e. Weight 1, W2, W3, W4, cool. W4, W3, W2, W1, cool, W1, W2, W3, W4, cool, W4, W3, W2, W1.
The rifle barrel was never more than "lukewarm to the touch".
No rounds were allowed to "stew" in the chamber, all were fired within ~10 seconds of closing the bolt.

Results
Disclaimer: I lost one velocity due to LabRadar failure, and one bullet blew up in flight (recurring problem for another thread). Though I got a velocity, it should be considered suspect. Due to the limited number of shots, the statistics are weak, but on the whole, I believe the conclusions are valid.

Brass weight vs Velocity

4 shot average of different weights vs velocity (3 shot for ~229 gr group).

Summary
Though I'm having ES fliers (2850 and 2929 in particular), which are certainly biasing the data, with 16 shots total, I think the results are robust enough to conclude that brass weight, and by extension internal volume, affects velocity.

That being said, I suspect it's almost completely negligible unless you have VERY extreme weight variations, or are shooting at such extreme ranges that you need single digit ES values. For perspective a single kernel of H1000 (~0.025 gr) is worth about 1 fps if you calculate velocity vs charge weight (e.g. 2900 fps / 66 gr = 43 fps/gr. 43 fps/gr x 0.025 gr = 1.1 fps)

This test spanned ~6 grains of brass weight variation in ~230 grains (±1.5%). If you cherry pick the worst case scenario, it only amounts to ~4 fps per grain of brass weight. If you cherry pick the best case scenario, it might be as low as 1 fps per grain of brass weight.

Hope you find this interesting.

Now I need to inspect the two extreme flier brass to see if I can figure out what's ACTUALLY causing my poor ES/SD issues in this particular rifle. All my other rifles/loads run less than 20/10 ES/SD without much effort. Something is wrong somewhere...

 

[ShtrRdy]

If you would be willing to take this one step further, you should sort the brass in terms of water capacity of the fired brass.

 

[rammac]

I don't agree with your assumption that brass weight (especially to that precision) relates directly to volume so I don't see where this analysis has any validity.

16 cases of the same brand of brass sorted by weight to plus or minus .1 of a grain should have included the corresponding volume data for each case in order to prove that the weight actually followed any changes in volume. I suspect that you would have found no real correlation between volume and weight if you had, at least not at the level of precision that you were using. If you sorted the brass in groups of 2 or 3 grains then you'd see a general correlation with volume change but even then it wouldn't be as strong as most people think.

I suspect that the weight variations reflected differences in the inside dimensions of the head and that those variations might have of had some influence on the velocity variations although I believe that there were other factors that had more of an influence than the weight variation.

 

[entoptics]

If you would be willing to take this one step further, you should sort the brass in terms of water capacity of the fired brass.

Thinking about doing that. Might get to this weekend. I have the brass sequestered and labeled, so it's a matter of figuring out a method for doing it precisely and correctly.

I don't agree with your assumption that brass weight (especially to that precision) relates directly to volume

Hrmm? That's not my assumption, that's yours.

This experiment was testing if brass weight had an affect on velocity. (FYI, it's actually in the thread title ).

...so I don't see where this analysis has any validity.

"Any validity". Seriously? Wow.

Methinks you don't understand how science works...Let me go ahead and attempt to explain it for you. I'll try and keep it simple so you can understand.

1) Find something you'd like to explain or understand
2) Consult existing knowledge to see if the question is already definitively answered beyond reasonable doubt
3) Formulate a possible explanation if not
4) Formulate a way to test your explanation
5) Analyze your test results and draw conclusions
6) Publish your conclusions so other scientists can critique them

7) Rinse and repeat. Dozens, if not hundreds, of times.

16 cases of the same brand of brass sorted by weight to plus or minus .1 of a grain should have included the corresponding volume data for each case in order to prove that the weight actually followed any changes in volume.

Didn't get to that, because as mentioned above, water volume wasn't what I was trying to explain/understand.

I suspect that you would have found no real correlation between volume and weight if you had, at least not at the level of precision that you were using.

So you haven't done the hard work of this type of experiment yourself?

Again, not about volume and weight...This particular experiment seems to show there is a correlation between brass weight and velocity, though as mentioned in #6 and #7 above, that doesn't mean it's universally true.

If you sorted the brass in groups of 2 or 3 grains then you'd see a general correlation with volume change but even then it wouldn't be as strong as most people think.

Again, volume vs weight isn't within the scope of this experiment, but this declarative statement implies you actually did do experiments addressing this question, or have a good validated source of information. Please share your results, or the quality reference you are using to arrive at this statement.

I suspect that the weight variations reflected differences in the inside dimensions of the head and that those variations might have of had some influence on the velocity variations

Again, not within the scope of my experiment, but I find it odd that "inside dimensions" isn't somehow the same as "volume".

although I believe that there were other factors that had more of an influence than the weight variation.

Again, please share the results of your experiments. As a scientist, I welcome any credible results, and am only seeking the truth, not validation or repudiation of my personal inclinations.

 

[LongBomber]

It would be interesting to take some case measurements of each case. Size the brass and measure the case groove, case rim dia and thickness, base dia right above the groove. If the extra brass is in external dimentions outside of the chamber then brass weight would make little volume difference.
If the brass weight is not in those locations it has to be changing the internal volume. Be it in case head thickness, flash hole dia, case wall thickness the extra brass needs to be somewhere in the case.
the specific weight of brass is somewhere around 8.7g/cc and h4831 is 0.893 g/cc. So it would stand to reason something like a 5gr difference in case weight may only make a .5grain powder weight/volume change.

 

[david g ranes]

It would be interesting to take some case measurements of each case. Size the brass and measure the case groove, case rim dia and thickness, base dia right above the groove. If the extra brass is in external dimentions outside of the chamber then brass weight would make little volume difference.
If the brass weight is not in those locations it has to be changing the internal volume. Be it in case head thickness, flash hole dia, case wall thickness the extra brass needs to be somewhere in the case.
the specific weight of brass is somewhere around 8.7g/cc and h4831 is 0.893 g/cc. So it would stand to reason something like a 5gr difference in case weight may only make a .5grain powder weight/volume change.

Didn't they say on Gunwerks information spots on their show one time that 7 grains of brass differences in weight was equivalent to one grain of powder don't quote me I may be remembering wrong. David

 

[Mikecr]

Easy to draw lines differently there

 

[Ingwe]

Thinking about doing that. Might get to this weekend. I have the brass sequestered and labeled, so it's a matter of figuring out a method for doing it precisely and correctly.


Hrmm? That's not my assumption, that's yours.

This experiment was testing if brass weight had an affect on velocity. (FYI, it's actually in the thread title ).



"Any validity". Seriously? Wow.

Methinks you don't understand how science works...Let me go ahead and attempt to explain it for you. I'll try and keep it simple so you can understand.

1) Find something you'd like to explain or understand
2) Consult existing knowledge to see if the question is already definitively answered beyond reasonable doubt
3) Formulate a possible explanation if not
4) Formulate a way to test your explanation
5) Analyze your test results and draw conclusions
6) Publish your conclusions so other scientists can critique them

7) Rinse and repeat. Dozens, if not hundreds, of times.


Didn't get to that, because as mentioned above, water volume wasn't what I was trying to explain/understand.



So you haven't done the hard work of this type of experiment yourself?

Again, not about volume and weight...This particular experiment seems to show there is a correlation between brass weight and velocity, though as mentioned in #6 and #7 above, that doesn't mean it's universally true.



Again, volume vs weight isn't within the scope of this experiment, but this declarative statement implies you actually did do experiments addressing this question, or have a good validated source of information. Please share your results, or the quality reference you are using to arrive at this statement.



Again, not within the scope of my experiment, but I find it odd that "inside dimensions" isn't somehow the same as "volume".



Again, please share the results of your experiments. As a scientist, I welcome any credible results, and am only seeking the truth, not validation or repudiation of my personal inclinations.

Bam!!

 

[entoptics]

Easy to draw lines differently there
View attachment 193902

What regression and statistics did you use to calculate your line? Did you get the same horizontal line when you applied your model to the 2nd graph with the 4 shot averages?

Or was it just MS Paint and wishful thinking?

 

[LongBomber]

What regression and statistics did you use to calculate your line? Did you get the same horizontal line when you applied your model to the 2nd graph with the 4 shot averages?

Or was it just MS Paint and wishful thinking?

Well just by eyeball on that chart there is a correlation between weight/speed. Looks like a roughly 10-15fps difference from low to high. Of course a sample of 100 brass each measured for weight, then fired 5-6 times each would give much better data but who is going to put 500 rounds downrange just to test that. A good test may be to take the lightest and heaviest single cases and fire each 5 times and see where the average fps for each is.

The simplest answer is likely to sort your brass and remove the outliers- get rid of the lowest and highest few and your velocity will show a lower es/sd. The same goes for bullet sorting, get rid of the outliers in weight and bearing surface length and groups will be more consistent.

 

[Mikecr]

What regression and statistics did you use to calculate your line?

My ~100 trillion synoptic buddies looked at the dots, put a mental ruler down, and drew a line.
Otherwise, it would take efforts in bias confirmation to arrive at your lines.
Too much effort.

Seriously, your spreads are too high for conclusion.
So throw away the outliers, and you have the simple average that I drew.

 

[Shadowwalker]

I don't agree with your assumption that brass weight (especially to that precision) relates directly to volume so I don't see where this analysis has any validity.

16 cases of the same brand of brass sorted by weight to plus or minus .1 of a grain should have included the corresponding volume data for each case in order to prove that the weight actually followed any changes in volume. I suspect that you would have found no real correlation between volume and weight if you had, at least not at the level of precision that you were using. If you sorted the brass in groups of 2 or 3 grains then you'd see a general correlation with volume change but even then it wouldn't be as strong as most people think.

I suspect that the weight variations reflected differences in the inside dimensions of the head and that those variations might have of had some influence on the velocity variations although I believe that there were other factors that had more of an influence than the weight variation.

If you weigh a case you have no idea where the weight is located. I agree weighing them with water is more accurate.
I used to see this with rimfire shooters which weighed each rounds on very accurate scales and then sorted by weight...."Brilliant Science"....as there are only 4 weight variations per ctg. brass, powder, bullet and priming compound and you have no idea where the variation are.

 

[cohunt]

I like experiment's - not all are conclusive though. Try the same test, but dont clean the cases, just brush the inside of the necks - reload exactly the same but dont use the dry graphite inside the necks.

See what happens to your es and sd

How are you measuring the powder weight?

Another member just recently did this and said that graphite powder was causing his "flyers" --- I want to try the graphite test in my rifle bit haven't had time yet



After that test, try the next size down on the mandrel (.282") and see if neck tension is affecting your spread

 

[LongBomber]

If you weigh a case you have no idea where the weight is located. I agree weighing them with water is more accurate.
I used to see this with rimfire shooters which weighed each rounds on very accurate scales and then sorted by weight...."Brilliant Science"....as there are only 4 weight variations per ctg. brass, powder, bullet and priming compound and you have no idea where the variation are.

But it is pretty easy to know where the weight is by measuring with tools every reloader should have, and also not knowing where the extra weight is- is a problem itself.