I didn't read carefully, but I think Dutch is right. That is likely an M-1949 that is poor quality down with chicken feathers. They are warm bags, but they come with considerable weight. The military made up for the poor quality insulation by adding more of it. I'll bet that some of these bags were stored compressed for as much as a decade. I can't find it now, but NATICK did a study on these bags and it is available in .pdf somewhere on the internet.
In my opinion, this bag is best left intact and kept in the car for emergencies. I still use mine in the back yard.