Let's go to the source and watch some carabiners getting broken!

• Black Diamond Neutrino Testing
• Black Diamond wire-gate, open configuration
• Metolious Carabiner Testing

While these videos show wire-gate carabiners, the idea is the same for a solid gate carabiner like the one pictured in your question. When watching the video, note the distinctly different failure modes: an open carabiner "bends" until breaking, while a closed carabiner "stretches" until snapping. This partially explains why, all else being equal in terms of construction and materials, a D-shaped carabiner is stronger than an oval: the D-shape better aligns the forces along the spine of the carabiner, leading to "stretching" instead of "bending."

These distinctly different failure modes can even be used to autopsy a broken carabiner and determine how it was loaded when it failed. For example, see this Black Diamond QC Lab warning about the even more problematic scenario of loading a "nose-hooked" carabiner.

Let's go to the source and watch some carabiners getting broken!

• Black Diamond Neutrino Testing
• Black Diamond wire-gate, open configuration
• Metolius Carabiner Testing

While these videos show wire-gate carabiners, the idea is the same for a solid gate carabiner like the one pictured in your question. When watching the video, note the distinctly different failure modes: an open carabiner "bends" until breaking, while a closed carabiner "stretches" until snapping. This partially explains why, all else being equal in terms of construction and materials, a D-shaped carabiner is stronger than an oval: the D-shape better aligns the forces along the spine of the carabiner, leading to "stretching" instead of "bending."

These distinctly different failure modes can even be used to autopsy a broken carabiner and determine how it was loaded when it failed. For example, see this Black Diamond QC Lab warning about the even more problematic scenario of loading a "nose-hooked" carabiner.