Milsurp you might get lucky and end up with a few tracer rounds here and there. A buddy of mine scored a box or two of tracer in the case
Save the clips after you strip the rounds off. You can resale those for a little profit.
That's what the military packages their ammunition in for storage.
I bought a bunch of 1946 manufactured 7.62x54r packaged just like that. Most inaccurate and dirty ammo I've ever shot, but the stripper clips are the best you're going to find for a Mosin.
Edit: Bought then for what I thought was expensive for the time, like $75 for 300 rounds. They came in a lead sealed sheet metal box, older design than the spam cans I was familiar with. It was a bitch to get open.
As the title says, they're old boxed packages of 15 rounds each, in stripper clips. I have around 15 of them. Most of the twine on them is still tied.
Resell them. Some high-roller collectors will pay big bucks for them, especially the rare ammo.
This is how I got some a couple of years ago in a lead box from AIM surplus. They were TULA I believe and did come in the cardboard and string. It had to be opened like a giant tin of sardines.
My Bulgarian rounds with stripper clips came packaged in those cardboard boxes with twine. I'm betting on that.
Let me know what ammo it is.