The cut edges of the capsule halves were a little off. The cut ends have to be flat for the end to end taped fit.
It's a simple fix to sand off the rough cuts with 200 grit on a sanding block.
Don't blindly drill the holes with the tip of a knife, take a moment to mark the locations with a pencil. You might find yourself erasing and remarking the hole locations a few times. Leave a little space between the two hole locations for strength.
Start the drill with the tip of an X-Acto knife.
Widen the holes and clean up the edges with a small diamond rat tail file. You want the hole edges clean and strong. Sometimes vacu-form parts can get thin.
Set the shoulder over the end with the drilled holes. Center it as best as you can visually and trace around the joint with a pencil.
Chances are the traced circle will be a little off center. Erase the circle and try again.
The pencil traced circle will assure that the shoulder will be centered.
