Model Proportions

Got a few problems with size of models…
My earlier work in 3ds max for Half-Life 2 was C-14 Gauss Rifle from Starcraft, but that ended griefly…

  1. It was invisible
  2. It’s size were like Phone, but it had to be more then adult man’s arm. I used Generic Units in 3ds Max.

So, how to make a proper size for model in 3ds max and what units are used for size and distance in HL2?
Fts, Meters or something other?

P.S. Sorry for grammar

1 unit = 0.75 inches for props/maps
1 unit = 1 inch for player models