Been hunting pasture land on our place which used to be part of an old plantation. I've found 36 mostly plain flat buttons and 2 coins (1867 shield nickel and a 1918 buffalo nickel). Obviously the workers watched out for their coins more than their buttons . All found using my F75 LTD.
Yeah it's pretty normal but every site is different. I'd be more interested in the civilian button vs military button count because if you can keep digging flat buttons you will find some good keepers.