Caseing weight and its effect

moosehunter

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Does anyone know if testing has been done on cases of different weight. Wondering what velocity difference one could expect on 2 identical prepped cases with identical load and bullet but 1 grain difference in weight. Looking at a 300WM and a 205gr Berger bullet.
 
Well, many one here will tell you that's it's not case weight but case "volume" that matters and they would be correct. But, 90% of the time case weight has a direct correlation to case volume and that other 10% the difference is not enough to matter anyways.
I try to sort my cases to +/- 1 grain and have seen no velocity differences especially on large cases like the 300 WM.
In fact, I usually run into issues when changing from one brand brass to another. You really have to watch that. I have a 25/06 that usually runs Winchester brass. But if I change to some Federal brass I have I have to change the load cause Federal brass is much heavier and therefore has less volume and has pressure issues. If I remember correctly the difference between the Win and Federal is 8~9 grains.
 
Casing weight usually means different case capacities. It is more obvious when changing brands. Whithout naming brands, I used 4 different brand cases for my 300WBY and noticed as much as 4 grains of water difference in capacity. If you are loading at exreme max and go to a heavier case, might end up locking up your bolt. I always do at least a QuickLoad or Gordons Reloading Tool calculation before I start loading different brnad (read weight) cases.
 
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for 1gr. on a 300wm I wouldn't worry about it but I can also show cases that have a 4-6gr weight difference but only .5gr capacity difference.
don't worry about 1-2grs if cases are from same manufacturer and lot#, different lots I would check capacity.
 
That's why when I was shooting benchrest competition I would buy as many new Lapua cases as I could afford and sort them by weight into lots of 20. THEN do the case prep.

I agree with what most have already said about case weight and volume. But checking by water volume gets messy and terribly time consuming.
 
I did a test once with a .223 load in a AR that was capable of sub 1/2" groups....I really need to redo and get pictures, and data now that I have a Labradar. The chronograph I had at the time worked about 50% of the time and I didn't trust it.

I loaded 7 cases of each brass brand I had (no weight sort or volume check) 6 brands including several military 556 cases. I shot 5 shot groups and then 2 remaining rounds into a joint group. I measured group size and distance vertically from point of aim. The joint group was pretty much exactly the smallest group size, plus the extreme spread vertically in size, (1.37" if I remember correctly) but all groups were still around 5/8" or less. If I had mixed headstamps that load would have passed by as a "bad load"
SO long story short, in THAT gun I only sort by headstamp and my vertical sight in changes slightly. Most of my other guns I sort by headstamp, and then into 2gr or less groups.- I don't like water in my reloading room and am content saying weight sort is "close enough" for volume.

I think the question may be gun and cartridge specific and you would need to shoot each case many times to get a "average velocity " to get any accurate data

*Sigh* the current component situation makes doing any testing like that a future project.....
 
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I use one headstamp when testing a load. My cases are weighed and grouped so they are all within 1 grain of each other in a group. Oddballs are taken to the range and left in the brass buckets.

A lot of my brass has been collected when we've done site-in days at the range in Sept. Culling can be fun.
 
Depending on the lot of brass, sometimes there is weight correlation, sometimes none.
The only way to know this much is through actual testing and measurement of both weights and capacities.
If you're going to do that, then you might as well just plan to measure actual capacities and remove any question about it.

But what is sought here is not actually about static weight, nor static capacity.
Instead, and ideally, our cases would match in dynamic expansive energy. This is the energy consumed from peak pressure to expand case walls through clearances and against chamber walls. The influence of this potential variance is complete by then.

Potential expansive energy goes beyond what we can directly measure, but we can indirectly measure & match it.
The energy to put case walls against chamber walls is tied to case diameter/area, loaded clearances, and tensile forces required throughout every expansion. It is intended to set the first two through sizing, but tensile forces are tied to brass hardness.
Well, so is spring back.

There is no useful information regarding either weight or capacity with new brass (in same lot). It was formed approximately and will never be in final form until we put it there with our best die (our chamber). That needs to happen before beginning with this matter.
You can have static capacities all over the place with same weight cases. Pull a weight matching case, smash it with a hammer, and now you have a case matching in weight that has zero capacity. Right? Match new cases by capacity, and some weigh differently with different wall thicknesses and web height/tapers. This affects tensile strength, affecting case dynamics (it's character).

In contrast, you can dip anneal cases, fire form them 3 times to stable with no more than neck sizing.
These cases should be fully formed now and sprung back from chamber walls given their individual character.
This is a good condition to measure H20 capacities.
For those cases matching in H20 capacity, after going through this process, you can be sure they're expanding and springing back with similar energy.

I have fully completed this with several cartridges now, studied the information along the way, and considered all potentials for a credible shortcut. There is only one potential shortcut: Once cases are stable as managed with your sizing plan, and with a well developed load, when you get a flyer -toss the case. Sayonara Marxist brass..
On the flip side, there is the possibility that your load doesn't care about this energy variance. That it appreciates any rough amount of peak pressure attenuation over a certain amount. Diminished returns often correlate with diminished variance of results.
So cases matched, and then Fl sized to never again match, can be just fine.
Back to tossing flyer cases!
 
Here's an experiment I performed awhile back.


To summarize...

Weight correlates with volume.
Volume/Weight does not correlate with velocity.
New brass produces lower velocity, despite lower capacity.

As mentioned though, this is for like head stamped brass. With different head stamps, there can absolutely be large differences in weight and performance.
 
A 1g difference in weight between cases in all but the tiniest of cases means nothing.
Have said this before, case weight is a good indicator that cases MAY have the same capacity, but after measuring volume to tenth of a CC and sectioning cases along the way, there is NO CORRELATION between case weight and case capacity.
The internal shape governs HOW the case behaves under pressure. A good example in 300WM is the fact that generally, Remington and Winchester cases weigh very similar….but their capacities are vastly different as to Winchester having very thick webs and Remington having thinner webs but thicker walls. You will see pressure sooner in a Remington case over a Winchester case for this reason.
Lapua brass keep their internal structure to very tight tolerance, that is why it has the reputation as being very good stable brass…when this varies, you get inconsistencies in hardness, spring back and even expansion rates, this is not good for accurate sizing, let alone a stable node.
Case weight is NOT the be all, end all, you need to measure volume, a crude way is to measure water weight, but to be precise, you need a 50/50 water/alcohol mix and measure CC's from a Burette.

Cheers.
 
Does anyone know if testing has been done on cases of different weight. Wondering what velocity difference one could expect on 2 identical prepped cases with identical load and bullet but 1 grain difference in weight. Looking at a 300WM and a 205gr Berger bullet.
My test was by weight in .223. Remington.
100 cases showed 6 heavyweights 12 on the light side 50 were "in the bracket " 93 to 94.3 grains. Remaining cases were set in their own group. SD was affected by primers, powder charges. Chronograph readings were within
20-30 fps of each shot. Sierra bullets weighed spot on at 69 gr.
 
I found where someone tested for case weight -vs- MV and there was little direct correlation.
It's pretty much what I would expect because there is more to it that is different all together.
BW v V All.jpg
 
If I have done all my work correctly, and having Muzzle Velocities from 2850 up to 2930... I went to sleep at the switch.

What caliber was he loading? Was he throwing powder charges in his sleep?
 

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