The rating is based on static weight, but our testing accounted for dynamic forces. We added something like 450 pounds of static weight, then pushed and swung and bounced and jostled the weight. The failure occurred when Dad practically jumped on the weight, adding his 200+ pounds, with quite a bit of dynamic force. This is when the s-hook opened, allowing the suspension to slip off.
When we re-tested with the larks head / cow hitch method, we could not cause a failure.
Obviously, we cannot emulate all circumstances, so it's difficult to be completely scientific. As such, we prefer to assign a conservative rating, and we strongly urge that it should not be exceeded, but you may take comfort in knowing that we tested substantial dynamic forces that would normally be exerted in a hammock. Swinging is strongly discouraged!
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