MCH heated shots question

I'm a new MCH, and I have a question about the heated shot versions. From my experience in the frontlines, once I use Gauss Barrel and get my heat level up to 50 and over, my shots automatically change to the heated versions.

Now in pve, I do the same, gauss barrel and heat >50, but my shots are still normal. I think I am missing something. Can anyone help me out? thank you!

Heated shots are unlocked at lvl 64 friend. ^^

Thank you! I've been looking for the level requirements in my skill window but as far as I know, there's no text about the level required to unlock it.
THanks for this as I've been going crazy trying to figure it out lol