At what levels do you get/stop getting different upgrade levels?
I thought there would be a list somewhere on the wiki but I couldn't find it.
Say I want to check at what levels you get, for instance Shredder rounds. This page shows that they are only available at levels IV to VII but at what player levels do those levels actually drop? Like Item level 1 drops for player level 1-X, item level 2 drops for player level X-Y and so on.
The ammo and weapon mods are divided into tiers, and these appear to have distinct lifespans:
Tier 1: Mod ranks I-III; Levels 1-18
Tier 2: Mod ranks IV-VII; Levels 19-42
Tier 3: Mod ranks VIII-X; Levels 43-60
So Tungsten and Shredder rounds will cease to drop as loot the moment you reach level 43. After that, the only way I've been able to add more of these without a cheat is to use the "Shepard gains doubles on anything he equipped" feature on a NG+, though strangely that list is captured by the game when you pass through the Conduit, not when you finish the game.
To maximize Tungsten/Shredder collection, I usually wait until level 39 to do the UNC: Rogue VI assignment, though that means a lot of game played without my class specialization. Geth-heavy missions generate a lot of loot too.