.45-70 Govt. ID

I have a 45-70 Govt. with no headstamp. The case is a coppery looking brass. The very flat copper primer 0.225 compared to 0.204 on FA loaded rounds. The head is rounded, not flat. It is a 405gr. lead bullet. There is a slight amount of botlle-necking to secure the bullet. My guess is U.S.C.Co. based on the look of the brass.

Anyone have a better ID or can confirm mine?

I would guess USC also, based on the rounded head and the high copper content brass case. These are often the cases that have the Farrington primers also, which your very flat copper primer sounds like.