I have no interest in tracking ammunition, but I'm pretty sure one of my players would be upset that I made his sniper rifle "so much more expensive" lol...
Tell him from me his ammo is free from now on.
Problem solved.

I have no interest in tracking ammunition, but I'm pretty sure one of my players would be upset that I made his sniper rifle "so much more expensive" lol...
tl;dr: if we know what we want the different ammunition types to do, it's easier to figure out how to make them do those things.
Do you think this is a useful approach to this topic, or is my inner engineer showing through too much?
To be transparent: we’re not rewriting the book. Errata means changing phrasing and numbers. A rewrite would be 2nd edition of the game, which isn’t in the stars right now.![]()
That was roughly what my intention was at the very start, even though I'm not an engineer
I hadn't set out specifically to pick a specific SOAK target like you're suggesting, but just by trial and error, I came up with SOAK 8 being the split point. This sorta makes sense, since it's where medium armor transitions to heavy armor.
Conceptually, HP rounds should be murder (more than just a bullet murder anyways) to someone in no or light armor. AP rounds should be most useful against heavily armored opponents (whether you want to pick this as SOAK 8 since heavy armor starts there or take it a bit higher/lower is up for debate). The problem becomes tricky with the gradation between armor types being so narrow (and having so few medium armor options).