All the code from Aum is created by me and tested by me, so it works for sure. It looks like your model has the origin in the wrong place; open Med, and then place it in the center. As an alternative, you can play with the x, y, z values from weapon's entity definition.
If this doesn't fix the problem, the problem is somewhere else. Try to use my snippet from Aum72 without adding anything else to it, and then add your own stuff line by line, until you discover what's causing the problem.