What year was this made? Marksman Pistol

[milko]

Hi guys, i have a question. i have an original (I think) Marksman Model MPR .177 cal. It's full metal and i am pretty sure that the full metal version was manufactured from 1955-77. I was wondering if there was a way I could find a more precise year on when it was manufactured. I think in the 70s the price went up to about $9. The price sticker on the box was $6.96. I looked all over the gun, box, instructions, and everything but I could not find any kind of date or serial number or anything. I will post pics later tonight or maybe tommorrow. Thanks for the help in advance.

-Adam