In a post-apocalyptic wasteland, a rogue munitions runner teams up with a failed government experiment and a resistance fighter to find his lost brother and help them end a brutal research project that experiments on children.

How about..? "After learning his brother is alive, a loner government transporter must work with a terrorist cell to stop the government experiment his brother and many children are trapped in."

All the pieces are there, but it could still use a rewrite for clarity.

The only clear part about a "rogue munitions runner" is the rogue part, I'm afraid. Are there any other words you can use to describe his job? Smuggler? Bomb expert?

You can take out the words "help them", since it is implied when you say he teamed up with them.

Other than that, the protag's goal is clear, but I feel it could be emphasized more. Perhaps you could start with that conflict ("When his brother goes missing . . .") in order to separate the two goals a little.

Great initial concept -- good luck!

While the goal seems solid, the way you describe the three protagonists is confusing.

I have know Idea what a rogue munitions runner is.

Saying, "A failed government experiment" is confusing and it took me reading it a second time to realize you were talking about a person.

While 'resistance fighter' is more clear, who is he fighting against? In fact you haven't told us who is experimenting on the children. Who is the bad guy?

I think you have an idea here but with a re-write it could become more clear as to what is going on.

Hope that helped, good luck with this!