Here is one expander button for Redding. http://www.gunstop.com/products/rel...ed-exapnder-button-375-caliber-30-to-375

Here is a thread on the topic there were several others. http://www.marlinowners.com/forum/3...eforming-30-30-brass-375-win-case-2.html Didn't read all of them but the gist is you want to have three or four steps up. Different posters used 8mm, 338, and 35 for the increments. I liked the stepped type expanders but they are less universal. A polished and well lubed tapered expander might do it in two passes especially if annealed.

This one is on sale Lyman: https://www.midwayusa.com/product/1011246697/lyman-neck-expander-m-die Most if not all die makers offer some type of tapered expander. Worth a Google as several threads came up on this as well as a couple different expanders.

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