sorting brass and bullet data for best accuracy

[Offgridkid]

I am having trouble with the whole "case weight" thing, for example, case #17 in my most recent batch has a weight of 170.40 grains and a volume of 45.46 grains (99% iso alcohol) and case #5 has a weight of 172.88 grains and a case volume of 45.22, less than case #17.

I turned the necks on both so there should be no expansion diffs or tension issues wrt the bullet, so why would weight even come into play? isn't the whole purpose to make sure that pressure is constant and that would be more a function of volume than weight in my opinion. Now, all else being the same, I would imagine that a heavier case would have, on average, thicker body walls and that might influence expansion and therefore pressure in the case.

am I missing the obvious. . . .would not be the first time ;-)

 

[Bart B]

I am having trouble with the whole "case weight" thing, for example, case #17 in my most recent batch has a weight of 170.40 grains and a volume of 45.46 grains (99% iso alcohol) and case #5 has a weight of 172.88 grains and a case volume of 45.22, less than case #17.

The lighter one may be more oval shaped and that reduces the space inside. Consider what happens if you flatten the case from its round shape down to completely flat; volume gets less and less until it goes to zero, but the case still weighs the same.

 

[Offgridkid]

I hear ya, that is why I check for that with a little contraption i made, whole case rides on a bead of bearings (no flex in case that way). In my example (case #5 and case #17) there was no movement in the indicator greater than 0.001). Before posting this I went back and checked each case at multiple locations, normally i just check in the center.

 

[Offgridkid]

forgot to attach contraption i made

 

[Offgridkid]

just occurred to me, I think your agreeing with me Bart, weight may mean nothing as two cases with identical weight have totally diff volume. Also see that if you measure volume you better make sure the cases are round or the volume you measure will change when the case expands to fill chamber after primer fires. . . in both cases, weight has no place in the story, just roundness and volume.

 

[drbill]

Well then it would be best to measure volume on once fired cases I would assume. ;-)