I suggest you begin with the protagonist as first mention instead of the antagonist even though you probably think the ant is more interesting. Spare no expense to make the antag as memorable as possible, but unless he is an anti-hero, it usually doesn’t work to pull the story along on its own. Even Darth Vader, arguably one of the most memorable of all time, doesn’t drive Star Wars on its own — hardly. I don’t believe he was even in Lucas’s first draft. Or was that the Death Star?

An aging cowboy must avenge his childhood friend, a lawman who is senselessly assassinated by an anarchist.

Now, the fact that you proudly display that the antag collects shields from his victims as a hook, is it really that grand to mention in the logline? I suggest you focus on adding the uniqueness to the protag, for that aspect will pay off much more for the length of the story.