Came to me in a flash

beag_nut · Apr 15, 2019

Came to me in a flash

There I stood, running my well-used .357 cases through my Lyman "M" bellmouthing die. Weeding through all of them for mouth cracks, and discarding about 10% of the nickel-plated ones, as usual. When it hit me: all the cases (both plain and plated) must conform to both of the industry-specified ID and OD dimensions (at the factory before being used), for obvious reasons. Therefore, the plated ones MUST have a thinner wall than the plated ones, to accomodate the extra added by the plating (both inside and outside). The nickel plating adds nothing to the wall strength, so the nickel ones have less brass material. Therefore the plated ones are weaker than the all-brass cases. Ta-da!

Walkalong · Apr 15, 2019

Nickle is less elastic than brass.

jak67429 · Apr 15, 2019

I don't know if they are weaker. they are harder and will not resize as often without cracking

ATLDave · Apr 15, 2019

beag_nut said:
There I stood, running my well-used .357 cases through my Lyman "M" bellmouthing die. Weeding through all of them for mouth cracks, and discarding about 10% of the nickel-plated ones, as usual. When it hit me: all the cases (both plain and plated) must conform to both of the industry-specified ID and OD dimensions (at the factory before being used), for obvious reasons.

While the possible utility of having completely uniform and standardized brass thickness at the casemouth may, indeed, be obvious, I'm afraid that the industry has not agreed. Some brass is thicker than others. Your conjecture is not unreasonable, but it's not the reason that nickel cases crack or flake more quickly under heavy sizing - it's what Walkalong said.

I've got some nickel brass that has many, many loads through it without cracking - but I'm not belling it very much. The less you work the brass, the less it will crack. This is true for plain brass, too, but the nickel stuff will let you know a lot sooner if you're really working the brass a lot.

ericuda · Apr 15, 2019

Sure are pretty though.

edwardware · Apr 15, 2019

The nickel plate is applied after case forming, to exactly the same case. No difference in brass; the nickel layer fits easily in the tolerance slop.

If you measure, you'll find inter-manufacturer variation in thickness is greater than the thickness of the nickel. You can probably see this visually if you look.

What IS different is that a crack in the very brittle nickel creates a stress riser in the underlying brass. The plating process may also embrittle the brass, but I don't know enough about the process to be sure.

Came to me in a flash

beag_nut

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