The MPi-69 was adopted by Austria to replace its aging MP40 submachine guns, and it included an unorthodox charging handle design connected to the sling. Clearly this didn't turn out to be such a great idea, because when the questions of Austrian military SMGs was revisited in 1981, the feature was removed. The MPi-81 is essentially the exact same gun, but with a sling swivel at the barrel nut and a standard sort of non-reciprocating charging handle where to old sling-attached type was originally affixed.
About Forgotten Weapons
At Forgotten Weapons I think the most interesting guns out there are the most obscure ones. I try to search out experimental and prototype weapons and show you how they work.