I've used that technique not only in my own .300 H&H's but a couple loaned for testing. It CAN work, but depends very much on the dimensions of the belt of the cases, and the chamber.
It's lot like "gently" resizing any of the older tapered cases that headspace on a rim or belt, instead of a substantial shoulder. It depends a lot on the fit between the rim/belt of the particular brass and the particular chamber. In a higher-pressure round like the .300 H&H this is more critical than in a low-pressure case like the .22 Hornet, but the results still vary.
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