After doing a little math, I find that the old "Diamond Select" Stargate is more in line with 1:18 scale (3.75 or 3 3/4). Good for custom G.I. Joes.
If you are into that scale. You can shrink heads on the Diamond Select Toys Stargate action figures with "HydroSpan 400" Shrinking Resin. This is some cool stuff. Good for turning 12", 8" and 6" figure head and accessories in to a smaller scale. The same company makes a resin for scaling up too. I don't know why more people don't know about this stuff.