I'm not sure I understand your question as far as what the risk is to a blow back system. Blow back refers to a type of system some weapons use to cycle the rounds. Some are direct blow back, some use a delayed blow back to slow down the cycling system, there's another one I'm forgeting, but I cant remember what they call it.
There is no Risk involved, just different systems. Some are more complicated than others. However all of them work as intended for the most part.
For example most semi automatic pistols are direct blowback. I think the MP5(and others) uses a delayed blowback and the AR platforms use a gas system or a piston sysyem now a days.