Stun Bombs to gain Rapid Fire for Rangers

Had been craving the Rapid Fire feat off the Waylayer tree, but needed 5 more ranks in that tree to meet the ore-requisite. So I sucked it up and took 5 ranks of Stun Bombs. Liking the Rapid Fire alright so far (wished it worked on Penetrating Shot), but those stun bombs really suck. I’ve tried them a few times against mobs (at full 5 ranks) and they have absolutely no effect. Of course, I’m level 50-ish now, but even a low level trap like fire trap does some visible effect on foes. Now I’m having to ask myself are 5 ranks of Rapid Fire worth spending 10 feat points on, because I’m getting nothing from my stuns.

Suggestions, Advice, Ridicule ???

You’re talking about Concussive Blast, right? If that’s the case, forget about it. It sucks.
Then, about Rapid Fire, 3 points is the maximum that you need to spend there.

Now, about how to get there, it depends on what’s the purpose of your build.
For solo play, I’m using this, and for groups/raids I’m using this.