Gunbreaker | Level 90 Opener/Rotation | Early Bloodfest | FFXIV Endwalker 6.0

Opener Used:
Lightning Shot into Early Bloodfest (Ensures aggro-snap + pot window + immediate NM + GF Combo).

**Running non-BIS Gear, so damage meter here is just but a means to see consistent damage via rotation craft.
**Since ACT skill table is not updated yet as of recording of this video, you won't be able to see Double down + Hypervelocity in the skill table.

Targeted GCD speed: 2.39 (for Burst Strike + Hypervelocity).

Notes and thoughts:
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This opener is not raid buff friendly, as the purpose of this opener is that you throw out all of your hardest damage hitting skill on cooldown (this is comfy for me). Use whichever rotation you feel comfortable.
Sonic Break, Double Down, and Blasting Zone can be weaved in depending on personal comfort and judgement (you can delay them until raid buffs are out, which is 3-4 GCDs in during openers).
Every No Mercy window MUST consist of a Burst Strike + Hypervelocity (alongside with your GF combo, Double down, etc).
If you end No Mercy window with a Burst Strike, your chances of landing Hypervelocity is VERY dependent on server ticks (this means that sometimes you will land the last Hypervelocity and sometimes no).
Use all Offensive CD's on cooldown and weave them per judgement.
Lastly, you should always enter No Mercy with 3 Cartridges. This is due Double Down takes two cartridges and GF takes 1. If you enter NM without 3, you will cause one of these skills to go adrift (even worst, won't be able to applied it under NM).

3 min. Reopener.
As you approach your 3 mins, keep in mind that this will be your hardest hitting damage window, with 6 cartridges (3 from standard 123 combo, and 3 from Bloodfest) ready to blast ;)
To maximize the damage you can deal here, you MUST enter No Mercy AFTER Brutal Shell combo, and delaying No Mercy NO MORE by 1 GCD, because you will be using 3 Burst Strikes + Hypervelocity here.
Because No Mercy can only fit 9 GCD's, your 3 min reopener window will look something like...

3 GCD's via Gnashing Fang Combo (Savage Claw, Wicked Talon).
2 GCD's via Sonic Break + Double Down.
3 Burst Strikes + Hypervelocitys
1 Solid Barrel (to finish off NM Window).
= 9 GCD's in No Mercy

Reasons why as you hold No Mercy after Brutal Shell is that if you use it on cooldown, you may or maynot be able to land the last hypervelocity via server ticks, so its safer to just delay 3 min NM by 1 GCD. This will however cause NM to go adrift by 1 GCD every 3 mins of the fight, so blame SE for not giving a duration increase on No Mercy pepega.