If it's a composite, maybe you're using carbon composite. It's abrasive on tools and very stiff. Not very useful for most jobs though. It's not threadable without inserts. And not many machinists want to contaminate their flood coolant systems with abrasive particles for a one off job. Carbon composite is usually laminated to shape instead of cut to shape so you can control fibre direction.

I mean radius corner as in add a fillet to the corner. Imagine putting a bead of putty inside the corner and shaping it with a 1/8" ball bearing which you slide along the corner to creat a rounded fillet. Filleted corners transfer stresses much more efficiently than sharp corners.

Erik, may I ask, were you using a sling with your Thompson?

http://upload.wikimedia.org/wikipedi...0px-Fillet.jpg
Example of non-filleted and filleted poles

http://upload.wikimedia.org/wikipedi...0px-Fillet.png
It is common to find a fillet where two parts are welded together



http://en.wikipedia.org/wiki/Fillet_%28mechanics%29

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I see. I wouldn't doubt that the use of the sling weakened it over time as well...