Ukranians carry M4’s? Because the troops in this video did.
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“The M4-WAC-47 is a Ukrainian-made assault rifle created by Ukroboronprom and American company Aeroscraft (a division of Worldwide Aeros Corporation).”
https://en.m.wikipedia.org/wiki/M4-WAC-47
We have millions of home built AR platforms here in the US and you can order the parts online. Why wouldn’t UKraine soldiers be able to do the same, in any caliber available including the 7.62x39 that is common with the AK?