September 1998

Does Internal Case Volume Affect Ballistic Performance?

We evaluated four different brands of brass, firing a common load in the same rifle, to find out. The answer was yes.

Aserious rifle benchrest shooter will go through a course of fire with a single case, reloading it on the firing line. The objective is to assure repeatable accuracy in a load carefully worked up to shoot groups measured in thousandths of an inch. Among the things the shooter eliminates by repeatedly using the same brass is the deviation in ballistics caused by internal case volume (ICV).

Even when a box of brass comes from the same lot and manufacturer, there’s no way to be certain of their individual ICV without taking measurements. The identical powder charge, bullet and primer in a case with an ICV of 0.66, for example, will produce a different ballistic profile than in a case with a...

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