Handbook of Reloading Basics by Robin Sharpless & Rick Sapp

Author:Robin Sharpless & Rick Sapp [Sharpless, Robin]
Language: eng
Format: epub
Publisher: F+W Media
Published: 2014-05-13T18:30:00+00:00

HULL CRIMP

At the opposite end of the hull’s base is the crimp, and no matter whether the hull is paper or plastic it needs to be positively crimped. One purpose of the crimp is to seal the end of the shell to prevent the shot from falling out and keep dirt from entering. The crimp also keeps the powder and shot properly packed for that micro-second when the primer ignites the powder and pressure begins to build.

The crimp is a patterned fold. Its design is essential for proper powder ignition and controlling the burn rate. Varying the depth of the crimp or otherwise changing a pre-established fold when you reload can quickly and surprisingly affect your shell’s pressure, so mind your crimp as you do the rest of your components and stick to the recommendations of the recipes you use.

A few years ago, two types of crimps were common, the roll crimp and the star fold. The roll crimp dates from blackpowder days. Blackpowder was bulky, at least compared to today’s smokeless powders, so it needed all the room it could be afforded inside a shell. Everything was packed in tightly and a small over-shot card (also called a wad) topped off a roll-crimped load before the crimp was applied. The crimp, when applied, rolled the hull firmly back on itself and down to the card, thus holding the powder and shot firmly in place.

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