Civil War reenactors go to great efforts to make sure their clothes and equipment are authentic to the era. So if you want your reenactment images to look authentic it is important that you pay attention to the background. Any large farm equipment, civilian clothes (including cargo shorts), small digital cameras, buildings, and paved streets need to be authentic to the 1860s. And of course if you want a really authentic look, convert your image to black & white.
On the serious side, if you want to know how to capture the muzzle flash of a Civil War era canon, read this article. In addition to the advice at that article, watch the person pulling the firing cord and trip the shutter just a bit before the cord goes taught. Getting the muzzle flash from a single canon is harder than capturing the flash from several soldiers shooting muzzle loading rifles.
Photo Data: Canon 7D. Canon EF 70-300mm f/4.5-5.6 DO IS USM lens at 70 mm. 1/200 sec, f/8, ISO 800.
When photographing a Civil War reenactment, be sure to capture some portraits.
Civil War Days, Lamoni, Iowa – the official site.