a standard action goes to less than a move action with rapid reload feat... (full round goes to move), also you misunderstand, a volley is a full round action anyways, it's that you could fire more than 1 attack/troop with concentrated fire. than again with quick draw you could still flip through muskets and reload later

All the same it's not the major unit I'm as worried about as lets say we had he bizarre senerio in which you had a million musket men with line of sight with an army of a million, you would be able to hit them all and plow them down at great distances without them even having the chance of a save, surly were there level 10s in there they could probably make the saves, and anything higher will more than likely make it in this bizarre epic thought experiment, so than could you see how double damage could do a real number on them? (especially if they must traverse the (130' range increment*10 max range increments) 1300' between them and you before really fighting back?

Now I know muskets are cool, but I suggest you spread it out more and don't toss such bonuses for the first level