[Fragor Prime] has a built in passive "Initial Combo Counter of 30"
[Corrupt Charge] ads 30 making your base Combo Count = 60
you are starting at x4 combo multiplier.

At this level [Blood Rush] is 240% critical chance bonus at all times.
With [Sacrificial Steel] that's total of +460% bonus (or +680% on heavy attacks) corresponding to 224% critical chance on standard and 312% on heavy attacks

Add [Amalgam Organ Shatter] for extra sauce on your critical hits which are always going to be Orange or Red from this point on.

I use [Primed Pressure Point] instead of [Sacrificial Pressure] because Umbra Polarity is harder to forma and unnecessary because at x4 combo multiplier the [Primed Pressure Point] pulls ahead and stays ahead of the curve in comparison to [Sacrificial Pressure]

If you have no plans to build combo using normal attacks or stance combos and are purely just going to jump around ground SLAM or HEAVY SLAM or just HEAVY ATTACK the world to death then from this point on you can focus on stacking damage and elemental mods and forgo any combo duration or efficiency options.

3 empty mod slots competing for array of damage options. The choice is yours what elemental combo you want to stack. But from several runs on sortie 3 enemies even with just [Life Strike], [Drifting Contact] and [Primed Fever Strike] I was able to reliably wipe the floor with heavy slams all mission long without any consideration of frame choice. Brittle frames with not much damage mitigation can live through a lot of damage just from [Life Strike] heals while dealing remarkable damage in return. Tankier frames that don't need Life Steal can dish out a little bit more damage by replacing [Life Strike] with an elemental mod.

I use [Gara] and she has enough tank to not need major life steal. Even running default polarity [Rejuvenation] is enough to keep her alive once this [Fragor] wipes the area clear you can rejuvenate your health in peace :)

I prefer the Grasshopper HEAVY SLAMS style so this build has no duration on your combos. just the base x4 should e enough for starchart and up to sortie 3 content.

My curent build using [Gladiator Might] to boost our bread and butter Crit Build, bigest elemental mod multiplier from [Primed Fever Strike] to get the base damage up and our lovely [Killing Blow] to speed up any heavy attacks we are doing and give them an extra OOMPH once they do land.