I don't think the approach you're considering will work like you're expecting. Even through pistols are simple machines, reliability calculations would be different for a pistol than something that's in continuous use like an air conditioner or a pump motor.

I think you'd be looking at the number of cycles (shots) between failures and the mean time to return the pistol to service (MTTR). Plus you'd need to consider the duty cycle of the pistol. e.g. how close together the shots are together - the effects of expansion/contraction due to heating and cooling could impact wear and tear (and reliability). e.g. shooting 1,000 rounds, one round a month will probably create less wear and tear than shooting 100 rounds in 15 minutes, each day for 10 days.

Too many variables. I suspect pistol manufacturers have a small number of different usage profiles set up they test against when they design a pistol. Maybe one for casual use, one for competitive use, one for military/police use. They have some proprietary algorithm they use to evaluate the failures in each of those categories, then modify those calcs with empirical data from repair returns.

Since as consumers we don't have access to any of that info, about all we can do is look at ad hoc info from users. Certain pistols and revolvers have a reputation for exceptional reliability. Others don't. No guarantee for a specific pistol/revolver though.

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Vegan by proxy.