Winchester Leader Staynless Box of 22 Long Ammunition - Incorrect Ammunition or Not ?

This Winchester Repeating Arms Co. manufactured yellow, blue and red cardboard box contains all 50 rounds of Leader Staynless 22 Long ammunition with copper cases and is in very good condition with light wear. Two 1/8" tears are present, one in each end flap and the right end flap hinge is just starting to split. The cardboard ammo tray has a 3/8" split down one corner. We believe this box contains incorrect ammunition because of the copper casings however, they may not have had brass casings available yet based upon the date code. The back panel states "New brass case.". The bottom of the box displays one patent number and states Pats. Pending. The end flap warning reads "CAUTION! / Dangerous within / 1 Mile". The copper casings display the "H-10" headstamp and the lubrication on the bullets has hardened from age.

Date of Manufacture: This style box was introduced in 1938 and was produced until 1946.

Note: This box is similar to the Huegel # WRA-55 L-1(a) variation. The difference observed is that this box contains copper cased ammunition. This box displays the "A" style bottom and the  #1 style end flap warning.

Date Codes Observed on This Box: MC48 6