Is it possible to make an animated model that changes the size? Instead of moving any parts i just want it to become bigger. Or are there any other possibilities for realizing a mushroom cloud?
Animated Model
Yeah. You need to animate it.
Rayban did same with his parachute model. You can find that with search.
oups. forgot that he used that. But does this work with milkshape? Would be a pity if i would have to change to blender because of this 
yo zero 
The trick is to do the “growing” animation directly in the .md3 of the model, then if you can do animations with milkshape u will not have to move to blender.
When you did the animated .md3 with the “growing” frames, just script-it to play the right frames when you need it ( look at the script function “startanimation” ).
… yes but i don’t know how. In Milkshape i can animate movements but I can’t animate scalations.
make a small nuke model explosion, copy the model scale it up higher, copy that scale it higher
put it all in the same place, hide them and script them to appear 1 by 1 making the one before it disappear. they should all start hidden
so the first one will be scale 1 and it will increment until it reaches for example- scale 50