5.56 Nato VS. .223 Rem

Sep 09, 2013

In very simple terms these are the differences:

The external case dimensions are the same. The difference is in the throat of the chamber. The throat is the distance from the end of the case to the start of the rifling.

SAAMI (Sporting Arms and Ammunition Manufactures Institute) specified the throat of the .223 Rem at .085 inch. In the 5.56  NATO the throat is .162, almost twice as much.

This means you can safely fire .223 Rem in any 5.56 NATO chamber but you may encounter higher pressure when firing5.56 NATO in .223 Rem chamber.

Often the 5.56 NATO is a little “hotter”, safety should not be an issue but reliable operation may be.

A shorter throat normally means improved accuracy but this is depending on the ojive (Where the shoulder of the bullet touches the rifling) of the bullet.

Military 5.56 NATO ammo will normally use thicker walled cases, have crimped in primers and a waterproof seal round the primer and bullet/case. The military obliviously place a greater importance on reliability over accuracy. The .223 Wylde is a compromise between the 5.56 NATO and the .223 Rem.

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