moosemike,

The .243 is illegal in some African countries for leopard, but not in others. A lot of JKH's hunting was done before there were "caliber" laws in many of the several countries he hunted.

Plus, some PH's are quite willing to allow clients to use a smaller-bore rifle IF the client has proven to be a good shot, or if the client has proven not to shoot well with larger rifles. I known of a woman who killed both Cape buffalo and white rhino with a 7x57 in the 1990's, in a country where the 7x57 was illegal for such animals. But she couldn't handle a .375, the smallest legal caliber. The PH let her use the 7x57, and both animals died due to 7mm injection.

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John Steinbeck