Oh sure, we'd like to shoot 250 rounds through it each day for a week or two starting cleaned and lubricated and adding some more lube now and then, but what can we do short of that to be "pretty sure" we have a working rifle with fewer rounds?

I'm thinking fire a couple mags before any functional modifications to be sure it works.

Then change out the trigger, choose an optic, etc.

Then do the real testing. What's a good procedure?

I've had bad history with AR's.