Brass weight... How important?

[entoptics]

I've done this a few times , and could not get brass weight to align with capacity . for me it's check capacity or just shoot it , weighing it is meaningless . I'll look to see if I can find a couple of my weights vs. capacity papers .

here is one

It's not surprising that the example you showed didn't establish a good correlation. I put all your data into excel, and did a few calculations. The extreme spread in your brass weight was 1 grain. The extreme spread in your water weights was 0.22 grains. The extreme spread in primer weights (not to mention variable powder residue if the brass weren't cleaned), was 0.06 grains.

Brass has a density of ~8 times that of powder or water. Therefore, a grain of brass volume = 0.125 gr of powder or water.

Assuming that the exact same amount of water volume ingresses into the primer, and the differences in weight were solely due to more or less brass, the primer variation alone would equate to 0.06*8 = 0.48 grains of H2O.

I applaud your efforts, and it's good science, but relative to the OP, you're putting a pretty fine edge on the question. I think the experiment would have different results if the variation being explored was much greater than the measuring tools' ability to resolve...

For ideally external dimension cases, a 1.6 grain spread in brass equals a 0.2 gr spread in powder volume, which for a 300 RUM is approximately 0.2% of the powder charge and/or H2O capacity.

A typical 26", 30 cal barrel ought to have a volume of ~450 gr of H2O, making the total expansion volume for burning powder about 550 gr of H2O in a 300 RUM.

Think about that. To change overall expansion volume in a 26" 300 RUM by 1% you'd need to see 44 grains of case variation.

All that being said, extreme weight variation in brass (greater than a few percent relative to the case weight), is likely an indicator of mediocre or poor brass quality, and therefore might affect precision for reasons unrelated to case volume.

Anyway IMO, if external dimensions are consistent, brass weight correlates to powder weight by a factor of ~8, and expansion volume (the real issue of concern) by a factor of ~10-100 depending on barrel length and caliber (short small bore has more affect than long big bore). If all your cases are within a couple of grains of each other, it's unlikely you're going to see much benefit in weight sorting.

 

[ar10ar15man]

maybe you should try some real world testing instead of just crunching numbers.
but than means not just case volume but ALL the steps in prepping long range MATCH quality ammo.

leave out one step and the results are meaningless.

again it is a game where the sum of all the parts add up on the target.
to each , their own,
i will stick with the small details.

It's not surprising that the example you showed didn't establish a good correlation. I put all your data into excel, and did a few calculations. The extreme spread in your brass weight was 1 grain. The extreme spread in your water weights was 0.22 grains. The extreme spread in primer weights (not to mention variable powder residue if the brass weren't cleaned), was 0.06 grains.

Brass has a density of ~8 times that of powder or water. Therefore, a grain of brass volume = 0.125 gr of powder or water.

Assuming that the exact same amount of water volume ingresses into the primer, and the differences in weight were solely due to more or less brass, the primer variation alone would equate to 0.06*8 = 0.48 grains of H2O.

I applaud your efforts, and it's good science, but relative to the OP, you're putting a pretty fine edge on the question. I think the experiment would have different results if the variation being explored was much greater than the measuring tools' ability to resolve...

For ideally external dimension cases, a 1.6 grain spread in brass equals a 0.2 gr spread in powder volume, which for a 300 RUM is approximately 0.2% of the powder charge and/or H2O capacity.

A typical 26", 30 cal barrel ought to have a volume of ~450 gr of H2O, making the total expansion volume for burning powder about 550 gr of H2O in a 300 RUM.

Think about that. To change overall expansion volume in a 26" 300 RUM by 1% you'd need to see 44 grains of case variation.

All that being said, extreme weight variation in brass (greater than a few percent relative to the case weight), is likely an indicator of mediocre or poor brass quality, and therefore might affect precision for reasons unrelated to case volume.

Anyway IMO, if external dimensions are consistent, brass weight correlates to powder weight by a factor of ~8, and expansion volume (the real issue of concern) by a factor of ~10-100 depending on barrel length and caliber (short small bore has more affect than long big bore). If all your cases are within a couple of grains of each other, it's unlikely you're going to see much benefit in weight sorting.

 

[entoptics]

maybe you should try some real world testing instead of just crunching numbers.
but than means not just case volume but ALL the steps in prepping long range MATCH quality ammo.

leave out one step and the results are meaningless.

again it is a game where the sum of all the parts add up on the target.
to each , their own,
i will stick with the small details.

I have tens of thousands of rounds down range, and have performed a myriad of "real world testing". Other than your presumptuous dismissal of my experience, I otherwise completely agree. The devil is in the details.

The OP wasn't about ALL the details though. It was about brass weight.

IMO, after working on the problem for a number of rifles, unless your rifle is a top tier long range rig, your shooting fundamentals are outstanding, and you've addressed most of the other variables in your ammunition (concentricity, neck tension, charge weight, etc. AND the ability to measure those variables accurately), then ± a couple of grains in brass weight probably isn't worth working on just yet...

YMMV.

 

[ar10ar15man]

but i do...nats *** details

and if he is taught early that details do not matter, when will he learn that the details are what counts at long range ?

I have tens of thousands of rounds down range, and have performed a myriad of "real world testing". Other than your presumptuous dismissal of my experience, I otherwise completely agree. The devil is in the details.

The OP wasn't about ALL the details though. It was about brass weight.

IMO, after working on the problem for a number of rifles, unless your rifle is a top tier long range rig, your shooting fundamentals are outstanding, and you've addressed most of the other variables in your ammunition (concentricity, neck tension, charge weight, etc. AND the ability to measure those variables accurately), then ± a couple of grains in brass weight probably isn't worth working on just yet...

YMMV.

 

[jimbires]

that's a good batch of brass . it does show that heavier weight brass does not always hold less volume . I think that is what the OP wanted to know . I always do this so I have a good water capacity to use in quick load .


OP , what you need to do is take a couple of the lightest weight ones , a couple of the heavy weight ones , and a few random weight ones . keep track of them while they are fire formed , then test water capacity . you will see for yourself if it's worth it .

 

[L.Sherm]

I can assure you weight sorting works. I had some Bertram 28 Nosler brass that was 6 grains difference from case to case that was brought to me because a reloader could not get rid of a flyer. Untill I weight sorted the brass I could not get rid of it either.

 

[MkJose]

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.

 

[misterc01]

I kinda found that whether I weigh the cases or not, if, after I have properly prepped the case, and the amount of powder I want to load in a case fits, and there is no compression, then they still shoot nice and straight. But I am a little new at all this, so always open to suggestions.

 

[L.Sherm]

I kinda found that whether I weigh the cases or not, if, after I have properly prepped the case, and the amount of powder I want to load in a case fits, and there is no compression, then they still shoot nice and straight. But I am a little new at all this, so always open to suggestions.

If you start out with cases like Lapua or ADG that are really consistent.
I just weighed my New 28 ADG Nosler case and theres only 1.25 grain difference from case to case. I still might separate them into 2 lots but that's pretty darn good

 

[ntsqd]

Going back to the example of all of the cases having been sized in the same FL die or better having been fired in the same chamber and are trimmed to the same length they would now have all the same exterior dims. The density of most metal alloys that have been cold-worked or forged doesn't vary much. Different alloys of brass could have different densities, but same mfg cases should be the same alloy. Certainly this is more true within a lot. Mixing lots might see a subtle alloy deviation.

So if the cases are all the same exterior dims and the metal density is the same, then weighing the cases will tell you, by calculation, what the brass volume is. Subtract that from the chamber volume and you have max powder volume. This would assume maximum powder packing, which won't happen, and not a compressed load, which could easily happen because it includes the case neck volume.

Depending on the need and application it may be splitting hairs, but to say that weighing cases is useless is not correct. There's a lot to be learned from doing so. If justified.

 

[Mikecr]

It is a lot harder to match and mange capacities than weighing cases and assuming everything else away. My earlier appeal to extremes was to illustrate that brass weight and brass shape can be totally different.
We form our cases to shape, which along with thickness and build affects capacity. And thickness also affects our ability to form to shape. Same with hardness, and sizing types/amounts.
This matters as initial confinement and initial expansion forces affect powder burn rate, pressure peaks and barrel timing.

In my experience, a capacity manged to match does not follow brass weight directly.
It would be nice if it did. But with some lots of brass there ends up being a good correlation, and not so much with other lots..
I just can't know it until forming and testing to see it, so where motivated to do so, I go ahead and do that.

With a past cartridge I started with 1,000 new cases of same lot.
I did weigh them and the weights were all over hell.. So I could cut all primer pockets to same depths, and trim all cases to same (wrong) length, and separate them into many groups or just biggest group by thickness (as measured at necks), and weight variance would probably be lowered. But my objective is not weight matching, it's capacity matching, with other matching attributes as well.

I chose to sort by thickness, and thickness variance to begin.
This quickly whittled me down to ~140 cases at same thickness, no variance.
I then cut pockets, turned necks to desired thickness, fire-formed 3 times with no sizing, trimmed cases to same (correct) length, measured H20 capacities.
This took me down to ~80 cases matching in everything, including capacity.
A lot of effort, a lot of waste, but direct.

For the hell of it I weighed all prepped, formed, matching and deviants of the 140 cases. There was a mean weight with reasonable variances, and what I found was that I could not pick out 80 capacity matching from deviants -by weight.
Out of 1,000, the only contribution weight measure provided for me was in finding 2 cases with missing flash holes and a retarded/liberal extraction groove.

On the 'waste', the ~860 culled cases,, I eventually sold them off at 3x what I paid for them. I've gone through 3 barrels with those same 80 cases, never needed further trimming, and you can bet they still match in capacity. They will last the rest of my life, just like this.

 

[ntsqd]

If two conditions are met, case lengths are all the same and have been sized or fired in the same chamber so that they all have the same exterior dimensions then what isn't brass volume in that chamber has to be air volume. That air volume is case powder capacity. The physics of it won't allow for anything else.

The density of the brass that the cases are made from probably does vary from lot to lot. Within one lot of brass from which the cases are made the density shouldn't vary enough to matter. These are pretty specific alloys, I expect the case mfg to exercise significant control over this. Whether or not the lot of cases is all made from the same lot of metal is something that only the mfg has control over. A change in lot of metal should result in a new lot of cases, but perhaps that isn't always so.

So if the exterior dims are the same and the weight of the cases is the same, then their powder capacities are the same. Really doesn't matter where within the case that brass is distributed. For it to be different means that there is either a variable unaccounted for or (more likely) they fail one of the initial two conditions.

EDIT: When I typed this I thought that it would be obvious, but as I stewed on it I realized that it may not be, so since I didn't say it I'm going to point out that the volumes of the flash hole, primer pocket and extraction groove are all deducted from the result above.

 

[ar10ar15man]

(was that the 30-30 ? and whose brass)

It is a lot harder to match and mange capacities than weighing cases and assuming everything else away. My earlier appeal to extremes was to illustrate that brass weight and brass shape can be totally different.
We form our cases to shape, which along with thickness and build affects capacity. And thickness also affects our ability to form to shape. Same with hardness, and sizing types/amounts.
This matters as initial confinement and initial expansion forces affect powder burn rate, pressure peaks and barrel timing.

In my experience, a capacity manged to match does not follow brass weight directly.
It would be nice if it did. But with some lots of brass there ends up being a good correlation, and not so much with other lots..
I just can't know it until forming and testing to see it, so where motivated to do so, I go ahead and do that.

With a past cartridge I started with 1,000 new cases of same lot.
I did weigh them and the weights were all over hell.. So I could cut all primer pockets to same depths, and trim all cases to same (wrong) length, and separate them into many groups or just biggest group by thickness (as measured at necks), and weight variance would probably be lowered. But my objective is not weight matching, it's capacity matching, with other matching attributes as well.

I chose to sort by thickness, and thickness variance to begin.
This quickly whittled me down to ~140 cases at same thickness, no variance.
I then cut pockets, turned necks to desired thickness, fire-formed 3 times with no sizing, trimmed cases to same (correct) length, measured H20 capacities.
This took me down to ~80 cases matching in everything, including capacity.
A lot of effort, a lot of waste, but direct.

For the hell of it I weighed all prepped, formed, matching and deviants of the 140 cases. There was a mean weight with reasonable variances, and what I found was that I could not pick out 80 capacity matching from deviants -by weight.
Out of 1,000, the only contribution weight measure provided for me was in finding 2 cases with missing flash holes and a retarded/liberal extraction groove.

On the 'waste', the ~860 culled cases,, I eventually sold them off at 3x what I paid for them. I've gone through 3 barrels with those same 80 cases, never needed further trimming, and you can bet they still match in capacity. They will last the rest of my life, just like this.

 

[Struggle]

(was that the 30-30 ? and whose brass)

Is there a way to ignore someone on this site?