This all made me curious so I went and did a bit of testing. Early results show that it scales off the crit damage that triggered the grenade. I tested on a Dahl with no crit buffs and a Jakobs with Type A & B crit. The results where consistent with both.

The grenade then gets grenade damage boosts from gear and guardian rank.

My testing so far shows:

Minesweeper Grenade = Crit Damage x (1 + COM Grenade dmg + Guardian Rank)

The grenade also procs Fire in the Skag Den which is calculated as such:

Minesweeper Grenade FITSD = Crit Damage x Fire in The Skag Den x Fire Multiplier

I tested this with 2 Minesweeper coms, one had +grenade damage and 2 FITSD, the other had no relevant boosts and 3 FITSD.

The following is pure speculation so don’t take it as anything else.

The minesweeper grenade is seemingly treated as a normal grenade. I believe therefore that Pull the Holy Pin not only lets it crit but possibly even allows it to reproc itself. If it can do this that would explain the wild variation in damage as successive procs would just get progressively more damage.

As an illustration of what I mean, suppose I have +40% grenade damage boosts. The initial crit I proc the first grenade off does 100 damage.

100 x 1.4 = 140

Suppose this then crits because of Pull the Holy Pin.

140 x 2 = 280

That is already massively bigger than the initial crit. Now suppose this procs a second grenade.

New Grenade Damage = 280 x 1.4 = 392

If this were also to crit you’d get 784 damage.

Which to recap the total damage is:

Total = Initial Crit + 1st Grenade + 2nd Grenade = 100 + 280 + 784 = 1164

1164 damage from an initial 100 damage crit!!! Although this would require a lot of luck. 3/3 Pull the holy pin I believe would still only allow you to get a grenade crit to reproc and crit once every 200 times you score a crit.

@sammantixbb I suspect your Traunt kill might of had this sought of rng applied.