SAAMI considers the use of 5.56 NATO dimension ammunition to be unsafe when fired in any commercial .223 Remington chamber, be it Match dimensioned or not.
5.56 should not be fired in any bolt action, single shot of any action type, pump or lever action rifle with the chamber designated as .223 unless the chamber of the firearm has been reamed to accomodate 5.56 NATO dimension cartridges.
5.56 NATO pressures normally exceed safe commercial .223 Remington standards and may lead to premature parts wear or breakage.
.223 Remington dimension cartridges can be safely fired in any 5.56 NATO dimension chamber.
The two drawbacks will be a slight loss of velocity, about 50 feet per second with most commercial loadings, and a reduction in the number of times a cartridge case can be safely reloaded before cracking or case head seperation becomes an issue.
Annealing the cartridge cases will add up to three more reloading cycles but most people do not do this or do not do this procedure properly.