I have TONS of hotel cards/empty gift cards/vanilla reload cards (twice the size, good for squeegees), but I don't think I've used them the way you're talking..I've seen your pics. I have used them to help make a very square edge at the dagger trunk exit. Anyway, I'll try it like you say.

I have milled fibers from us composites, but I was planning to use carbon just to try to prevent this from happening again. Does that just make the rear of the dagger trunk more likely to get torn up? Is carbon even stronger in that situation or is it too brittle?

I hit a log floating under the surface, but the front of the dagger shows no damage at all. The rear got damaged from getting jammed into the trunk.