Chamber Cast
A casting poured into a rifle chamber to capture its exact internal dimensions, used to identify or verify the chambering.
A chamber cast is made by plugging the bore and pouring a low-melt alloy or sulfur-based compound into the chamber, then removing the hardened impression once it sets. The result is a precise negative of the chamber, throat, and leade that can be measured with calipers and a comparator. Gunsmiths reach for it when a rifle’s markings are missing, worn, or simply do not match what the chamber actually is.
The cast reveals the true chambering, the freebore length, and where the rifling begins, which is invaluable for an unknown or wildcat barrel. Comparing the cast against a chamber reamer print or against published headspace figures lets a smith confirm whether a barrel is safe to feed and what brass it actually needs.