Just recently, I had actual need for my FA. Several times, my bolt did not close, not really sure why though I think the case was at an improper angle as the round was almost in, and undented when pulled out before firing. My chamber was not dirty.
At any rate, I tried hitting the forward assist and I could not generate enough pressure with my hand for it to move my bolt/carrier forward. It would have taken a boot stomp. As it was, to pull the charging handle back and remove the round took a boot. Aside from those situations when there was some sort of hang up, I also had several situations where there was no binding of any kind, yet again it was too difficult to smack the FA with enough force to cause it to go fully into battery. In those situations I simply pulled the charging handle back a little and let it fly home. What a let down.