Charlie: I was waiting for a Parker expert to step in, but I'll go ahead and...step in it
358 guns were made with "Plain Steel" which was used for a short period in transition from "Decarbonized Steel" c. 1875. The decarbonized steel was probably sourced from Remington; plain steel possibly.
The Parker ads found by EDM and John Davis only mention Parker making Laminated and Twist barrels c. 1878