While these cartridges seem to be the same, there is a difference and it matters.
by Patrick Sweeney
Gunsmith’s should have the SAAMI-published list of unsafe caliber combinations detailing cartridge and chamber combinations that can be force-fit into a rifle and the combos that ought not be there. One surprising (to some) inclusion is the .223 Remington and the 5.56×45. While they are not the same and should not be used interchangeably, .223 is generally safe in the 5.56 but the reverse is not.
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