When most cops carried a revolver, the .357 Magnum was considered the best manstopper available with the right loads. Now few folks depend on a wheel gun for self-defense, but if you do the .357 Magnum might still be your best bet.
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I love me some 357 magnum. It's just about all I carry nowadays, either a 4 inch Model 65 or a 2 inch Charter Arms Magnum Pug loaded with Hornady's Critical Defense.