The gun needs help, very underperforming for an Exotic Heavy. Catalyst should be Field Prep for more reserves and faster reload which the gun needs, also Bait and Switch for more damage which the gun also needs.
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For starters I would switch range finder out with reconstruction. Second I would make the catalyst a ramp up head seeker which would state "xenophage now does precision damage, landing 3 back to back body damage greatly increases precision damage and releases a large explosion that scorches nearby enemies. Strong against unstoppables".