That's not the problem.
The problem is that Hordes have NO counters. Random hits don't hit enough.
Work Blast and Flamers like the Void Mine, pick a Unit, roll a D6 for each model in it up to a maximum.
Assault X
The Number of Attacks this weapon may make is equal to the number of models in the targetted unit, that are within range of the Weapon. to a maximum of 6 for D3's, 12 for D6's and so on.