Lock and Load: The Reassembled Machinist Guide

[Myon88]

Yup, main thing is,

1. It's a waste to put Potion after Lead Shot. It's the weaponskill with the most total potency for the 1 GCD you spend to cast it, so you want it to be buffed by as many things as possible.
1.5 Also if you Potion after a Weaponskill that's been buffed by Rapid Fire - you're likely going to clip a GCD because the Potion animation takes a long ass time for some reason.
2. The GCD you spend to cast buffs, itself, doesn't do any damage, so better to get it out of the way before the fight (like you did with Hypercharge).
3. The way to get the most benefit from Rapid Fire is to prioritize using it on Split Shot above Slug and Clean, since the latter will be instant already thanks to ammo while Split Shot will always have a cast time.
The most number of Split Shots we can get it to affect (without overlapping procs) is 2, hence the Split, Slug, Clean, Split, Slug, Split, Clean, Slug sequence*, with Rapid Fire used at the start of the bolded portion.

If you combine all that logic with your opener, you'll arrive at the one in the OP of this thread.

*Technically you could do Split, Slug, Split, Clean, Slug, Clean, Split, Slug like you wrote.
The reason you can't (if you follow the opener in the OP) is because there's no place to put Rapid Fire that early. Hot Shot gets canceled into Potion, then Lead Shot into Reload, and then you go into our Split/Slug/Clean weaponskill sequence - no room for it.