FG45? No such thing.
If you mean the VG1-5, they were crude beyond belief:

If you mean Stg45, they weren’t designed for the Volkssturm, but for the infantry:

The Stg45 pioneered roller-delayed blowback, which was then incorporated into most of HK’s designes.

,i never heard about that weapon,maybe is a less known weapon,the volkssturm where the old men who fought for the german army in the last moments (they needed more soldiers)
