[NoStr0m0]

Really easy.

Create your basic shell polygon. That is, the shape you want your cross section of the shell to be.
Create a UV map for your polygon, planar, hiting it side on, not full on. Now hit Shift+L to chose the Lathe tool.
As you can see, it can't go past 360 unless you type in a higher value.
Now, chose an offset so it has a basic spiral shape to it.
Depending on which axis you chose and where you place the center, you may get several shell shapes.
Ok, make sure Make UVs is selected.

Now, go to the Map tab and chose UV to Weight. Chose the U or V, you'll have to experiment, give it a name and create it. Your aim is to have the tip of your shell be full 100% weighted while your base is at 0%.
When you're done, hit h for size or Shift+h for scale and hit n for numeric. In the falloff chose weight map. (make sure the weightmap you created for the shell is selected) and then proceed in reducing the size of the shell. You'll notice the tip is shrinking faster than the base.
You can also move the tip more by using the move with the Weight falloff selected if you think it sticks too far out.



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