I wasn't a helicopter pilot/ warrant officer in the army, just an aircraft structures mechanic but yea I don't think I've ever heard anyone call them choppers, if anyone did I never noticed, but i probably would've remembered though because I'd be thinking "get to the choppa " in my head. We always called helicopters "birds" mostly, I personally didn't really hear helo used as much, I mean I did every now and then but I heard people using the word helo more on the civilian side after I got out from people. So for me at least we mostly said bird, or 60 if it was a Blackhawk, shithook if it was a Chinook, etc. Chopper to me just sounds too tv-ish , sorry, just rambling on and remembering and missing being in lol