This is an answer I gor on another forum
Looks like one of the "new model" sleeping bags issued from 1990's on.
The ones I used in my day had "Navy duffel coat" type buttons.
Used one of the new models with zipper during my last reserve call up some years ago though.
If I remember correctly the new model was an evolution on the 3 layer design concept of the old model (i.e. with an inner "washing layer", a mid quilted "heat layer", and an outher cover layer.
During my basic training year we used to change the inner layer of the sleeping bag for a new one from the depot once every month.
If I'm not wrong think the sleeping bag comes in 2 models.
A standard model, and a "jaeger" model with better insulation properties (comfortable in underwear mode down to -28 - -30 C) for jaeger and recon units. We hade some of the prototypes of the jaeger models on testing in my unit, when I did my basic year. They were made by Ajungilak based on their Tyin cold weather sleeping bag model (though with zipper opening, and were a great improvement over the old model maggots we used at the time.