It's not unreasonable. Those mags were designed specifically for the M16 when they were invented, and then they became a NATO standard later on, and all a manufacturer has to do is get the size specs for the magazine well down and tune their proprietary (keep that in mind) bolt to not interfere with it. Magpul deviated from a standard STANAG magazine pattern too, so it's not going to be perfect for everything.
"Universal" almost never means "perfect". I'm glad that the problem is acknowledged by a guy like Stumgewehre, looked at objectively and fixed in a simple manner.
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