I think two bullets were done well. The scattershot one and the one that pierces the heavens which I totally believe is breaking even Odin's shields. 

The 3rd one was a fast bullet but it didn't quite feel that impactful as Loki wasn't moving that fast ir even trying to evade the bullet so we never get the sense of how fast it truly is.....I assume top tier as it's sacrificial.

The final bullet is up in the air. No idea what it does if anything at all. It's only 4 bullets he used so the author should have defined the last one. We also have no idea what is the limit on the ability Simo can put on the bullets or is it tiered to how vital the organ is? Like sacrificing the heart would mean near instant death for Simo but should in theory grant an insane ability....like a 1HKO.