I've never owned an AR. All my guns I drop the hammer at the last safe place I'm at before storing.
Thats how i do it. Just what i was taught. Grandad thought it would fatigue the spring. However, some say it doesn't hurt them at all. Growing up with a cock on closing sporterized m1917 with a heavy spring, made me think grandad was probably right with that one. I wont argue one way or the other and feel it should be left up to the individual.
