77E shotgun Gift

A Marine Corps friend of mine forwarded a shotgun to me. He spent over 30 years in the USMC and traveled the world.
The story of this shotgun was that it was in Vietnam and then traveled to the Philippines where he got it.
The shotgun has some hard use as the outside metal is pitted and the woods show dents and scratches. The bore is bright and shiny up to the last 1/4" where there is some darkening.
A sling is on the shotgun but I cannot make out the numbers. It is newer than the shotgun and made of canvas. The recoil pad is still in nice shape and pliable.
I know little about this shotgun but really thanked my friend for it as I'm a 'Nam vet.
https://i.imgur.com/iLzFJUy.jpg

https://i.imgur.com/Cz6gkix.jpg

https://i.imgur.com/OL5df7B.jpg

https://i.imgur.com/KDWlNxV.jpg

https://i.imgur.com/yw6XrSL.jpg

https://i.imgur.com/bs8ICnF.jpg