Well is it jamming before it lifts it, or is it just not putting enough pressure to even stop the bb? If it can't even stop the bb, you have a problem with the hopup where the arm isn't going far enough.
More likely though, you don't have even pressure on the r-hop. You need the r-hop to apply even pressure to the bb along the entire length of the patch. This is where the soft nub comes in. Unlike the regular nub which applies pressure to a specific spot, it will conform to the r-hop and apply pressure along the entire length.
You don't NEED the soft nub, but it sure helps. Also, you can use other things besides the m-nub, most of the materials you already have at home. Go look in my r-hop database thread, and there are multiple threads talking about what nub material to use and how to put it on.
The reason we aren't answering very specifically is because we don't know every detail. We don;t know if there is a problem with the hop chamber, if you installed something wrong, or even if you just didn't sand the patch down correctly. We are trying to generalize our answers so they may help.