Voi: Most of the brass shells that you see are processed client-side. When I was testing the Brass message, to write about it on that same page that you linked, I only ever noticed it getting called by the AWP, and maybe the Scout? Since the client's brass shells fade away quickly, the message is sent to tell them to create a brass shell in that place that lasts longer (which is apparently only used on high-powered rifles).
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No longer around. Thanks your support, everyone! As always: