Not often enough to make for an actual trend. Not even during the "annus mirabilis" year the Army of Northern Virginia - a single field army - had between June 1862 and June 1863.And it's worth mentioning that the Confederate rebels often killed a lot more US troops than they lost, though this may be due to other factors like initially crappy US leadership and in any case a lot of Northerners were also rural agricultural gun-users.