maybe its the detail32, because i've made custom projectiles in blender and they worked fine.
You need to make 2 empties, called Shape and Detail32. Parent your mesh to detail32 and then parent detail32 to shape.
Then export. There was a tut on rtb wiki but rtb wiki doesn't even work anymore. Atleast for me. Also if you're making vehicles, to make collision you need to make a collision box. Just a regular box around your mesh where you want your collision to be and name it either Col or LOSCol. It'll work without that but you get alot of console spam ingame. Then make an empty called col0 and parent your collision box to col0 and col0 to shape. You won't see the collision box ingame because its not parented to detail32.