There are many question around the .223 / 5.56 round. Is there a difference, what is it it, and can the rounds be fired interchangeably?
Firstly, Yes! There is a difference.
Although the 2 rounds look the same, there is a difference. Although both fire the same .224 and are very similar in length, the pressures, however, differ when fired. It comes down to the chambers of each rifle and the throat (or Leade). The leade is the area at the mouth of the barrel before the rifling. The leade of a 5.56 chamber is larger than that of the .223, hence the .223 is less than the 5.56.
What does this all mean?
This all boils down to what round can be fired safely out of a rifle. First, always refer to the owner’s manual to determine the correct ammunition to use and do not deviate from this. If it is unclear, contact the manufacturer directly for assistance. You may have read gun magazines and on the Internet have that a .223 chambered rifle can only shoot .223 ammunition, whereas a 5.56 can shoot both .223 and military spec 5.56 ammunition safely.
Again this is due to pressure differences, with larger pressures developed when 5.56 rounds are fired in a .223 chambered rifle.
What can happen if the incorrect caliber is used?
When 5.56 ammunition is fired through a .223, a number of malfunctions can exist, which include case and rifle damage, excessive wear and malfunction.
If selecting a rifle for the first time, determine what you will be using it for, evaluate the supply of that ammunition, and purchase the proper rifle for your needs. Play it safe, always check your owner’s manual and stick with the proper ammunition.