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This is labeled .223/5.56 nato. What is the barrel officially marked? I understand you can use .223 ammo in a 5.56 but what is the barrel marked? — 2 Answers

by Jacob Isebrands, from CO, United States Asked on January 26, 2022

Name CBC Industries AR-15 Complete Upper Receiver Pistol Kit, .223/5.56, 10.5in (3.5)
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Answered by Ethan, Gear Expert, from IL, United States, on January 31, 2022

The CBC Industries AR-15 Complete Upper Receiver Pistol Kit is stamped as 5.56. So you can use both 5.56 and .223.

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Answered by Jacob Isebrands, member, from CO, United States, on January 31, 2022

The barrel is stamped as 5.56 Nato

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