While it's true that each weapon type has base projectile / damage falloff for it's own type, form my tests, the bar does equate to the value 100, regardless of weapon type. I'm currently running a Scout Rifle (5 Range), Auto Rifle (5 Range), and Rocket Launcher (5 Blast Radius), and the bar increases the same amount for each weapon (You can tell the increase by going over and highlighting the opposite masterwork perk [I.E, Crucible or Vanguard], and it'll show how much the bar was increased by that 5 Bonus. Just my testing, anyhow. Regardless, all weapon types have different values associated internally, so +5 Range on a Shotgun would barely be noticeable opposed to +5 Range on a Scout rifle, which has extremely different falloff values, so I can see where you'd like clarification on just how much each bonus helps your weapon.