870 grooved barrel top

[Mbuck]

870 barrel question. Is it common for the smooth non vent rib barrel to have grooves along the top like the receiver? I'm a newbe for starters, just purchased this 870. Based on date code it is a 1953 vintage. Never seen a barrel like this and wondering what's up. Any info would be greatly appreciated. Thanks!

[Virginian]

Those used to be fairly common. Supposed to help keep down reflection on a plain barrel.