Imo, not worth the risk shooting in a gun of any kind without a fully supported chamber. MG ammo won't blow up your barrel, but in a pistol it can blow the case head off and wreak havoc in that area in front of your face and in your hand.
Also, while I don't see anything on the headstamp about pressure, the St+ indicates a lacquered case. Sometimes that stuff can get nasty in your gun and cleaning it may be more trouble than it's worth. BUT, its your gun, ammo, face and hands, so therefore, your decision. Good luck.