**Yes - well, maybe.**

[Abalone armor is pretty tough.](http://www.livescience.com/3800-abalone-armor-toughest-stuff-theoretically.html)<sup>1</sup> While not bulletproof, they're certainly strong, and comparable to some body armor designs currently used by humans (see [Lin & Meyers (2005)](http://www.sciencedirect.com/science/article/pii/S0921509304008809)).

Their shells are made from interlocking tiles of calcium carbonate, reminiscent of certain tiled arrangements for bulletproof vests (the ones made of ceramic). However, the tiles are arranged irregularly, in a way that makes it harder to penetrate them. They're bound together with a coating of protein "glue". Abalone armor could be mimicked to create new types of bulletproof vests, or the creatures could develop a stronger version of it.

So, I think that some sort of bulletproof armor is possible, if it is based on a system like this.

I'm aware that there's an ongoing debate in the paleontological community as to whether the armor of ankylosaurs and related dinosaurs was bulletproof. As far as I know, the evidence does not support or destroy the hypothesis that it was.


---
<sup>1 An [abalone](https://en.wikipedia.org/wiki/Abalone) is a member of a family of sea snails.</sup>