Jagdkommando was gracious enough to send me a STG-556 for T&E last year for the Vickers M4 Mod/Staff class. Ran 1200 rds. through it, 400 of Prvi Partisan M193, 400 of Federal XM193, and 400 of USGI surplus M193 circa 1972. Nary a bobble.....100%.

Compared to a Polish PMKMS folding stock AKMS.......





Compared to HK G36C and 416.





And compared to my Colt 6920.