Originally Posted by LouBoyd
I agree with JE Custom in principle. I recently however ran calculations using Quickload to measure the effects of a 1 grain weight difference. The concept is that cartridge brass has a specific gravity of 8.56 compared to water with a specific gravity of 1.0. Therefore a case with 1 grain less brass increases the case capacity by 0.117 grains of H20. .
My calcuation assumed a 300 Win Mag shooting 190 grain Bergers at 1000 yards. I assumed SAAMI seating depth and 75 grains of VV-N560 powder ( a load I use) with a 24" barrel. The increase in case volume (in this example from 93.0 to 93.117 grains reduces the camber pressure and in this calculation dropped the velocity from 2959 to 2957 ftps. The calculated drop at 1000 yards (standard metro and sea level) changed from 311.7 inches to 312.2 inches. A difference of 0.5 inches.
Is a half inch at 1000 yards important? It could be the difference between winning or loosing a 1000 yard benchrest match. It could matter if you're shooting prairie dogs.
I also checked the effect of a 1 grain change in propellant weight. Going from 75 to 76 grains changed the velocity from 2957 fps to 2999 fps, a difference of 40 fps which changes the drop at 1000 yards by 9.5 inches. I think any long range hunter would agree that's significant.
Can brass weight vary without a proportional change in case volume? Yes. When brass is fired the case walls and neck conform to the chamber dimensions, but differences in the case head diameter or the volume of the extractor groove are not reflected in the interior chamber volume. If the weight difference is in the neck it can have other other effect which affect velocity and accuracy.
Neither sorting for weight uniformity or volume uniformity is a guarantee that the walls and necks are symmetrical.
For it to make sense to sort brass to 1 grain it should be obvious that one must also measure charge weights to 0.05 grains or better to make weighing cases have more effect than charge weight. I do both. My powder scale resolves .02 grains and I weigh each charge to +/- .02 grains. To get better uniformity of the case head diameter and extractor grooves I don't mix headstamps or manufacturer batches.
Very good post and a good explanation to some of us that can't express ourselves as well.
First, I agree with the 1 grain batch simply because it is a starting point and gives a good
indication Of the batch quality. and from that 1 grain batch I select brass with the same
exact weight for precision shooting, and if there are enough pieces that are under .5 grains
to load 20 or more I use these for long range hunting also.
I like many also drop powder charges that are as perfict as possible to zero difference.
It does make a difference and if I can lower the Standard deviations by 1 or 2 ft/sec I will take
the time. Is it nessary ? probably not most of the time but confidence is important when
that once in a life time shot comes along.
A rifle is only as good as the ammo and the shooter. so it is worth the trouble to me.
J E CUSTOM