Why Our Carabiners are the Best in the World
This is one of the reasons you must always be aware of how your equipment is positioned. It's also why you should consider using two biners or a captive eye carabiner.
Don't think that steel biners necessarily are better in this regard. Years ago a caver, concerned that his rack could break open a sleeve, switched to steel biners and asked us to test one for him. We looked at the thin, stainless (lower tensile strength than 7075 aluminum) screw sleeve and knew the results would be scary. Indeed, the sleeve broke at under 400 lbs. (1.6kN). The caver had been carrying all that steel around for nothing.
Weak sleeves are a necessary evil of the old conventional rivet and notch carabiner design, because the nose has to be very wide to be strong and therefore the inside of the sleeve has to be big, too, and that means the sleeve wall thickness is thin and weak. The original Keylock design still tended to use a wide frame nose to get the required closed gate strength and so the sleeves were still not very strong. On the carabiners we made for other companies, we were able to make some changes and improve the strength a lot, making them stronger than any similar biners.
For our own Rock Exotica carabiners, we were able to start with a fresh sheet of paper (or rather a fresh 2 Gigs of RAM) uncontaminated by old thinking and cost accountants telling us we had to lower costs. We designed a patent pending imrpovement to the Keylock that is stronger than a conventional Keylock. It allows the frame nose to be more compact, actually fitting entirely inside the gate. Then we make the sleeve (both screw and auto) inside diameter as small as possible which means the sleeve wall is very thick and incredibly strong. The inward sleeve strength approaches the minor axis strength and is actually about 10kN! (We rate it conservatively well under this.)