Some people were mad as fuck that it wasn't 7.92x33mm. A few people were also beyond infuriated that some of the aesthetic details differed (especially the lower receiver). The actual technical specs and drawings for the old Sturmgewehr family was lost in the war, you can find fake ones on the internet, which those guys looked at but couldn't use because they're actually bogus, and the lower in particular is apparently a super obnoxious shape to stamp.
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At least, that's what HMG claimed, I don't know just how true that claim is.
Personally, I'd be fine with something mostly aesthetically similar in .300BLK, using the tilting bolt and long-stroke piston, but with a simplified FCG, and then some little cast metal cover piece to stick on the side of the lower to emulate the right look.
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I remember someone in particular who insisted the project would be worthless if it didn't faithfully replicate this entire mess.
Yeah, it really was kind of a hunk of shit in a lot of ways, handy gun for those who had it, and economically smart in using kinda shitty steel for less critical parts, so you only have to use a little bit of nice steel for the important ones, but that also means the things are not built to last. I suspect the idea of a bayonet lug was floated but rejected because the gun really wouldn't be up for much vigorous spearing, the magazines do not last long either, as a whole these were almost certainly expected the used up until they broke, then trashed and replaced with a new one.
The original ones are not good shooters for someone who has one. I once heard from someone who owned a transferable one that mismatched parts isn't too uncommon, because you'd cannibalize parts from other (also broken) rifles to repair yours.