JP Enterprises Silent Capture Spring

[NugginFutz]

Easy to set up an automated machine to repeatedly compress a spring similar to the environment the spring would see in the rifle. Run the test through an environmental chamber at the same time to simulate temperature variations (seasons) throughout the year and you have a reasonable test that is repeatable giving you the data to average out the 500k round claim. This is a standard industry practice to extrapolate expected lifetime of any product.

Some of these test rigs are surprisingly unsophisticated. Simple motor, pulley and crankshaft with a counter, in many cases.