Talk:Overbore

How do we treat different case capacities in different brass?

I wanted to add .338-378 Weatherby Magnum and .338 Xtreme to the table, but noticed that the case capacities vary within several percents: for example, with the former, our article states 125 grains of water while http://kwk.us/cases.html states 132 grains. This is not unusual since only the external geometry of a case is determined while the internal one varies with different manufacturers, which often select different wall and head thicknesses.

1. We really have to round all the capacities to about two significant digits BTW to avoid false precision, and the overbore ratio as well.
2. However, even in that case the variation may exceed those two digits: my calculation shows a spread of 15 (14.7) to 16 (15.6) cm for the .338-378 and 19 (18.97) to 20 (19.7) cm for .338 Xtreme.

What do we do? (As a side note, the bore diameters are only determined to three significant digits, and the bore area should be as well in the table.) Ain92 (talk) 21:07, 18 May 2022 (UTC)

• Pinging colleague @Francis Flinch: who has been the main author of this article. Ain92 (talk) 14:32, 20 May 2022 (UTC)
• P.S. As a side note, it would be appropriate to add some less-known anti-tank cartridges from {{Anti-Tank Rifles}} but I have absolutely no idea where to get case capacities for them( Ain92 (talk) 14:40, 20 May 2022 (UTC)

Case capacities or volumes can and do significantly vary between cartridge case manufacturers and even (generally to a sub 2% degree) production lots. See .300 Winchester Magnum for a high 8% difference between manufactures and QuickLOAD for a .35 Whelen sub 2% example. The examples point out, one can not presume cartridge cases are very uniform. The QuickLOAD article points out it is wise for reloaders to use water to measure the actual internal volume of involved cases to obtain an average. The observed significant/exceptional differences between manufacturers gave rise to mention these in the .300 Win Mag QuickLoad database. Like weight, case capacity measurements are a good indicator for reloaders of component uniformity. For .338-378 Weatherby Magnum the QuickLoad database assumes 137 grains (8.9 ml) maximum case capacity, overflow. The .338 Extreme is not contained in that database. A_bore is specified quite exactly by the C.I.P. in their TDCC publications that presume the C.I.P. bore. Changing a bore by adding or subtracting a groove is generally not very significant.--Francis Flinch (talk) 16:27, 20 May 2022 (UTC)