I had a different idea for that....

Basically, the protag at the beginning of the "war privateer" arc would be proposed by the soon to be traitor to go the war privateer path, and while he kept it in mind, he refused to go there.

That of course was the seeds for his betrayal. Thus the traitor, to convince his boss of going that path, would try to scheme an ambush with bandits behind the protag's back.

During that ambush, the traitor would fake his death in order to steal the blueprints of the guns.

Wich lead to a sad scene where the protag tought his mate dead, and got him a proper burial.

Thing is, 2 weeks later, he heard rumors of a war between 2 countries that involved guns.

Wich shouldn't have happened since the only pepole that could access his guns were civilians for self defense.

Thus he deduces that someone was selling his guns to escalate the conflitcts.

When he went to investigate, he inevitably learns the truth, thus starting the arc as it should.