New build, failure to extract spent shell, charging handle hard to pull back

[Klem]

For some reason it is a common problem with the grendel. Happened to me. After you run 20 rounds through it.problem will go away.

It is not a common problem with the Grendel.

There will be some technical issue common to both of you, but there's no evidence it is common. Or peculiar to just this calibre.