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It doesn’t state, but I would assume that it should work with a 45acp build, right? — 1 Answer

by Joe, from IL, United States Asked on September 2, 2021

Name CMMG, Inc Upper Receiver Parts Assembly AR15-MK9/M4
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Answered by Tom B, Gear Expert, from IL, United States, on October 18, 2021

The ejection port might not be opened up enough. Per the manufacturer: The Mk4 platform accepts standard AR15-style magazines, and is the most versatile of the CMMG platforms, especially with the .22 LR, 5.7x28mm (Conversion), and 9mm conversions.

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