Hammer push-off test is one of many checks I use before buying a used revolver.
It is a safety check.
If you have a bathroom or postal scale of some sort, place the muzzle on the scale plate, push down on the hammer spur and see how much pressure it takes before it pushes off.
This is a better way to check than guessing how much pressure you are using with your thumb.
Jerry Kuhnhausen states if you can get to 16#'s, you do not have push-off.(so no need to go any further).
Jerry also states that "some experts" state 10-12#'s.
I am in the 10-12# camp and never had a safety issue.
I have worked on some friends revolvers in the past that you could just slightly push or look at it wrong and the hammer would fall.(not safe at all).

Clarence

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B.E.Master in&outdoor
D.R.#99