If you intend to spam charged shots with the Volatile Impact Mixture, then you end up wasting ammo and total possible damage that way. You can deal a high, consistent DPS and get more value out of spamming just normal shots boosted from tier 2C; especially on a Dreadnaught.
The only point of using charged shots then is to clear out a group of at least 4 grunts. Tier 4A can help save you the ammo cost for that in the long run.
It is true that Single Shots would result in more total damage on it's own, but the burst damage with a Charged Shot and 3-4+ Blisters on a Dread is still something to be considered. This is also taking into account that the build is tailored for solo play, where maximizing ammo economy over burst is generally unnecessary, as you have enough freedom to spam resupplies simply for HP or grenades and still have many leftover.
