And I'm no expert communicator; I meant to say a +/- 1% spread.
Thanks for point out my error.....or whatever.
brass weight sorting
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Thanks for point out my error.....or whatever.
And weighing cases is the most accurate way to determing case capacity.
I've takes several primed new unfired cases of the same weight, and filled them with the same amount of water by weight. The water line came to different levels in the case neck. Proof to me that filling cases to the case mouth ain't a good way to measure case volume.
The chamber's the same size for all cases fired. Cartridge brass is homogeneous enough that all cases with the same weight take up the same amount of space in the chamber. So when the case is fired and expands to fit the chamber completely, then and only then is its true capacity worthwhile.
Weigh cases. Save water. Do it right.
I've takes several primed new unfired cases of the same weight, and filled them with the same amount of water by weight. The water line came to different levels in the case neck. Proof to me that filling cases to the case mouth ain't a good way to measure case volume.
The chamber's the same size for all cases fired. Cartridge brass is homogeneous enough that all cases with the same weight take up the same amount of space in the chamber. So when the case is fired and expands to fit the chamber completely, then and only then is its true capacity worthwhile.
Weigh cases. Save water. Do it right.
A study of my chronograph data examining the effects of capacity and weight on velocity:
Holding all other variables approximately equal (primer, seating depth etc), case weight only explained about 30-35% of the variation when examining velocity differences across the chronograph, while capacity is roughly 70%. I have established this statistically by regression analysis in different trials, but this depends on the method used to determine case capacity, and type of brass. The two variables are definitely related (somewhat linearly), but only to a point.
Measuring water capacity on flr brass is not sufficient. Re-read the posts above by mikecr. Short version... accurate case capacity measurements are likely to shrink ES/SD more than case weight. Both methods are effective at reducing chrony spreads.
Determine what matters most (time vs accuracy) and make your call. Learn to read the wind and you'll make more kills than with either method combined
Holding all other variables approximately equal (primer, seating depth etc), case weight only explained about 30-35% of the variation when examining velocity differences across the chronograph, while capacity is roughly 70%. I have established this statistically by regression analysis in different trials, but this depends on the method used to determine case capacity, and type of brass. The two variables are definitely related (somewhat linearly), but only to a point.
Measuring water capacity on flr brass is not sufficient. Re-read the posts above by mikecr. Short version... accurate case capacity measurements are likely to shrink ES/SD more than case weight. Both methods are effective at reducing chrony spreads.
Determine what matters most (time vs accuracy) and make your call. Learn to read the wind and you'll make more kills than with either method combined
Mikecr
Well-Known Member
Bart, as implied new cases & FL sized cases are not in the right condition to measure capacity.
Also, the implication that cases eventually expand to the chamber, so weight is all that matters, is dead wrong.
It is INITIAL CONDITIONS that hold the largest affect on peak pressures and internal ballistic timing.
Yeah a case expands to the chamber but:
-Neck tension changes pressure & velocity & tune
-Seating depth changes pressure & velocity & tune
-Anything about the primer, flash hole, or powder lay changes pressure & velocity & tune
-And initial containment(loaded case capacity) **** sure changes pressure & velocity & tune
Also, the implication that cases eventually expand to the chamber, so weight is all that matters, is dead wrong.
It is INITIAL CONDITIONS that hold the largest affect on peak pressures and internal ballistic timing.
Yeah a case expands to the chamber but:
-Neck tension changes pressure & velocity & tune
-Seating depth changes pressure & velocity & tune
-Anything about the primer, flash hole, or powder lay changes pressure & velocity & tune
-And initial containment(loaded case capacity) **** sure changes pressure & velocity & tune
Buffalobob
Well-Known Member
Weight sorting is a very good way to get rid of odd ball cases which will give you flyers.
I use to test dive cylinders. Water was used to measure volume, before, during and after the pressure test.
But before this could be done the water needed to be compressed a few times in the cylinder to release the air that it contained. It was surprising how much the volume changed with each compressing.
Water volume measurement is useless without compression.
Also cases will change their internal volume with each firing.
A once fired case will have a different volume to the same case after it has been fired a number of times and has case head expansion, been trimmed a few times, has loose primer pockets and is due to be chucked out.
But before this could be done the water needed to be compressed a few times in the cylinder to release the air that it contained. It was surprising how much the volume changed with each compressing.
Water volume measurement is useless without compression.
Also cases will change their internal volume with each firing.
A once fired case will have a different volume to the same case after it has been fired a number of times and has case head expansion, been trimmed a few times, has loose primer pockets and is due to be chucked out.
If case capacity was directly related to pressure, velocity and "tune" (musical notes?), then my tests years ago using new unfired and neck sized twice fired cases would not have produced their groups at 1000 yards atop each other. Muzzle velocity would have been different and therefore, so would bullet drop. The only difference was accuracy with new cases was much better.
Note that a 30 caliber bullet needing 40 pounds of force to push it out of the case gets pushed out when pressure inside the case is about 530 psi. Most handloaded cases have that amount or less; mine are much less. And the case is pressed against the chamber at only 1000 psi. So I don't see any way how case capacity at primer ignition has any significant effect on peak pressure and/or velocity. Show me strain gage time vs. pressure/velocity curves with different case capacities at primer detonation that prove it and I'll change my mind.
The above aside, this is a most interesting discussion.
If case capacity at primer detonation has to equal across all cases for all shots to have the same pressure curve shapes, consider this. Neck only sizing is well known to require cases be full length resized after several firings. Those cases get bigger each firing. They soon cause bolt binding. Their capacity increases with each firing. Maybe this is why so many top high power competitors get best accuracy full length sizing all the time. Virtually all high power matches are won with and records set with full length sized (or new) cases.
Note that a 30 caliber bullet needing 40 pounds of force to push it out of the case gets pushed out when pressure inside the case is about 530 psi. Most handloaded cases have that amount or less; mine are much less. And the case is pressed against the chamber at only 1000 psi. So I don't see any way how case capacity at primer ignition has any significant effect on peak pressure and/or velocity. Show me strain gage time vs. pressure/velocity curves with different case capacities at primer detonation that prove it and I'll change my mind.
The above aside, this is a most interesting discussion.
If case capacity at primer detonation has to equal across all cases for all shots to have the same pressure curve shapes, consider this. Neck only sizing is well known to require cases be full length resized after several firings. Those cases get bigger each firing. They soon cause bolt binding. Their capacity increases with each firing. Maybe this is why so many top high power competitors get best accuracy full length sizing all the time. Virtually all high power matches are won with and records set with full length sized (or new) cases.
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Mikecr
Well-Known Member
Topshot, I'm sure NASA would deareate purified water to determine capacity at various pressures atmospheric. But shooters do not need to consider any of this. We are not certifying our loads, but qualifying them.
Hell, the argument here is whether to measure at all!
And yes, volume does change until fully fireformed and held stable with minimal sizing(NOT FL sizing). This is when H20 capacity should be checked, and not before.
So what happens to velocity as volume goes up? It goes down. Volume up = velocity down.
How does this seem rocket science?
Bart, many BR shooters do not even verify the measure of their powder, yet anyone with sense knows that powder amount affects velocity and tune.
If you had the sense to test capacity variance with velocity measurement, instead of anecdotal hogwash, I believe you would learn something here.
But for the rational:
EVERYTHING about initial containment affects pressure and timing.
Hell, the argument here is whether to measure at all!
And yes, volume does change until fully fireformed and held stable with minimal sizing(NOT FL sizing). This is when H20 capacity should be checked, and not before.
So what happens to velocity as volume goes up? It goes down. Volume up = velocity down.
How does this seem rocket science?
Bart, many BR shooters do not even verify the measure of their powder, yet anyone with sense knows that powder amount affects velocity and tune.
If you had the sense to test capacity variance with velocity measurement, instead of anecdotal hogwash, I believe you would learn something here.
But for the rational:
EVERYTHING about initial containment affects pressure and timing.
I have done such tests. Only velocity changed; spread did not. But I thought that would happen so I didn't learn anything.
Neither did several of us developing .308 Win loads for a new match bullet using different new cases weighing 160 to175 grains using metered powder charges. We didn't use the load having the lowest spread in velocity or peak pressure; it had the worst accuracy. The selected load had average spreads but even with 3/10 grain charge spread in new cases it shot half moa or better at 600 yards in over twenty different rifle's barrels. If I and others like me can do that with anecdotal hogwash in our veins, so what?
Mikecr
Well-Known Member
I can think of rim diameter, extraction groove depth & width, primer pocket diameter & depth, and flash hole diameter or chads left from punching of it.
And outside diameters and lengths cannot be assumed matching, but must be made to match to qualify in the question. If you FL size, you can be assured they don't match, because all that brass area is springing back & forth to new dimensions -everytime.
New brass does not match either.
The case weight in itself doesn't mean anything, until measured to show that it does.
So if a case departs from others by 2gr, you would have to measure & compare it's capacity aginst the others to see if it actually holds different capacity anyway. And how could you be sure that cases matching in weight hold the same capacity?
So you might as well just measure the capacity of your cases and be done with it.
Aside from laziness, is there really a reason not to measure it?
Would it hurt a thing to do so?
