Dating Eley .22 Short

Yesterday I ran across (at a very reasonable price) two full bricks of Eley .22 Short Pistol Match ammunition, green box with black and white letting, no child warning. “MU-57” is stamped inside the end flap of each box. Would that be 1957? Along with those, I got two more bricks of Western .22 Short pistol Super Match, yellow boxes, also no child warning. Lot stamping inside the end flap was PK92, which I take as being 29 September 1959.

I actually plan to shoot these eventually, as I have several early .22 Olympic rapid fire target pistols. Big mistake or not?

It does look like S-4. I erroneously said the Eley did not have the child warning, but it does, so obviously from the early 1960s or later… It is only the Western which does not. Anyway, the only headstamp is “E” Also has 5 silhouette targets on the end flaps.