WEIGHING CASES TO IMPROVE ACCURACY
A 223 Rem case, full to the top with Titegroup, holds 24 grains of powder.
The case, filled to ~ 1a quarter inch from the top with Titegroup, holds 22.3 grains of powder.
24 – 22.3 = 1.7 grains.
A 22-250 case, full to the top with Titegroup, holds 36.3 grains of powder.
The case, filled to ~ a quarter inch from the top with Titegroup, would hold 36.3 – 1.7 = 34.6 grains of powder.
36.3/24 = 1.51
34.6/22.3 = 1.552
223, 40 gr. bullet, 5.5 Titegroup, 2063 fps
22-250, 40 gr. bullet, 5.5 Titegroup, 1857 fps
2063/1857 = 1.11
1857/2063 = .90
@ 5.5 grains of Titegroup, 223 vs. 22-250; volume decrease ~ 66%; velocity increases ~ 11%
223, 40 gr. bullet, 8.5 Titegroup, 2678 fps
22-250, 40 gr. bullet, 8.5 Titegroup, 2418 fps
2678/2418 =1.107
@ 8.5 grains of Titegroup, 223 vs. 22-250; volume decrease ~ 66%; velocity increases ~ 11%
Between 5.5 and 8.5 grains of Titegroup, 40 grain bullets, velocity varies, inversely, about 1% for each 5% change in case volume.
How does case volume vary with case weight?
A 223 case weighs 96 grains, a 22-250 case weighs 159 grains.
Case weight and volume are:
223 24/96 = .25, 22.3/96 = .23
22-250 36.3/159 = .23, 34.6/159 = .22
223 and 22-250 cases have internal volume of about 23% of case weight.
Case volume changes, (inversely), about 23% as much as case weight varies.
A case weight goes up 5%, internal volume goes down ~ .23 X .05 = .115 = 1.15%.
As internal volume goes down 1.15%, velocity goes down .0115 X .2 = .0023 = .23%
5% of a 223 case ~ .05 X 96 = 5 grains.
5% of a 22-250 case ~ .05 X 159 = 8 grains.
Why do we weigh cases?
