The common Union sack coat issued by the Quartermaster had Eagle buttons with a plain shield. Haversacks were also made by different vendors and while serving the same purpose, had minor differences.

http://www.cjdaley.com/
The above site has authentic reproduction Union fatigue blouses (sack coats)and other items for sale. He also has a page dedicated to some of the research he has done to enable him to make these items as accurate as possible. You may find some answers there. I also have a few other items on my web site "Civil War Show and Tell" that is linked on this post.

Good Luck