Now I know what you're thinking
"Bitch, get the f*** outta here, it's the crappiest mutator"
I just played as a railgun boiler, and here's what I found.
While yes, you DO have to charge up a shot, here's the benefits:
INSTANT dig-in time, so you don't have to wait 5 seconds before you can click a target.
When you click a target, it only takes about 3/8ths of the time to take the shot, unlike gassing.
You can fire early (albeit for less damage)
No short-range limit, so you can dig in, click, and click again for a quick short-ranged shot.
If you're an elder, or the marine is wearing light armor, A FULLY CHARGED SHOT WILL INSTA-CRIT a marine, virtually taking them out of the fight until someone helps drag them out.
Not only that, but it makes the tank crew SERIOUSLY re-consider it's next method of attack, as your shots chew away NEARLY 10% OF THEIR ITEMS PER SHOT. This means 60-90 seconds of long-ranged contact with you, and the tank is either dead or in full retreat.
... My conclusion? ... it's actually a viable alternative to gassing!