Is it true that upgrading a 5 star non primo to level 50 turns it primo?

Been grinding to get a primo thermal brella or primo butan blaster and somehow got both of them as regular 5 stars instead.

I saw people saying that if you upgrade the 5 stars all the way to level 50 it becomes primo, but others were saying this was untrue and didn’t work.

Is it true? I really don’t want to grind more for this weapon