your bullet should not be attached to the model in any way. Get the direction the gun barrel is facing and store that in a property associated with the bullet. Then assign your bullet's starting position to match the tip of the gun barrel. Then start moving the bullet, which should be independent of the tank at this point.
amountOfBullets = 10
dim bullets(amountOfBullets,8)
The second dimension of 8 would hold these values:
1 - x position
2 - y position
3 - z position
4 - x direction vector
5 - y direction vector
6 - z direction vector
7 - speed
8 - object number
The direction vector is the where the gun is pointed at the time you fire that bullet. (make sure the vector is normalized) Then you just move the bullets in the array.
for i = 1 to amountOfBullets
bullets(i,1) = bullets(i,1) + bullets(i,4)*bullets(i,7)
bullets(i,2) = bullets(i,2) + bullets(i,5)*bullets(i,7)
bullets(i,3) = bullets(i,3) + bullets(i,6)*bullets(i,7)
position object bullets(i,8),bullets(i,1),bullets(i,2),bullets(i,3)
next i
