NOTE: The "medium" sized shirts are the same dimensions as the original, and would have been what a soldier was issued regardless of size.
Perhaps every soldier, at some time during his term of service with the Union army, was issued a wool/cotton domet flannel "quartermaster pattern" shirt. Derided as "insufferable hair shirts" by some soldiers who wore them, this style of Federal shirt was nevertheless produced in the millions and was no doubt widespread among the eastern theater armies. Today in the hobby these shirts are far too lacking in number among Federal living historians. The truth is that no Federal impression should be without a domet flannel issue shirt, and a spare kept in the knapsack will prove to be invaluable on damp, chilly nights, or when a change out of a wet cotton shirt is needed in the warmer months. When worn in the field the domet flannel shirt adds an undeniable no-nonsense air to any Federal impression that cotton civilian shirts fail to do.
The other barrier to widespread use of these shirts by living historians is that the original issue shirts produced by the US government were entirely handsewn. Accurate reproductions of these garments should be entirely handsewn, and now, for less than half of what it would cost to have it made by one of the many makers of authentic goods, you can make one of these shirts for yourself!