I use Black Diamond Camalots, but half the time I need to extend the sling with a quickdraw, which is a waste of gear. I’m considering replacing the original single sling with a doubled loop of Spectra cord so I can extend it when I need it. Is that safe?
The elephant in the room of doubled cam slings is that they are weaker when you extend them. But the strength of doubled slings extended to single loops is unknown because cams are tested and rated with the loops doubled. Since I haven’t heard about cam-sling failures, I’m guessing that the extended double loop, though not as strong, is still strong enough.
There are other, larger concerns. You mention that you would use Spectra cord to re-sling your cams. Spectra cord is a bear to cut and knot. Knots tied in this slick, rascally stuff easily come undone, usually when you’re counting on them not to. Further, the thumb loop on Black Diamond Camalots is engineered to work in harmony with the webbing sewn onto it. In particular, Black Diamond tucks a double layer of webbing between the cable and the webbing loop. That extra layer of webbing acts to distribute the load evenly across the thumb loop. Your jury-rig job won’t have the doubled webbing. The cord-on-cable contact will be minimal—in a mild fall the cord could pinch the thumb loop into a “V,” deforming it and possibly cutting the cord.
So, like exporting democracy to fun-loving jihadists, the notion of retrofitting your cams with extendable cord loops sounds brilliant, but actual implementation is fraught with risk and economic pratfalls. The good idea is to re-sling your BD cams when they look worn. Black Diamond will re-sling its units for $5 each. Allow two to four weeks, and don’t ask for anything weird or wacky—they will only resling their cams using factory methods and materials.