Danny, from what I can tell from the limited records available, the 12th Arkansas Battalion was not used specifically as a "sniper" or sharpshooter unit, at least until Vicksburg was surrounded and besieged.

In fact, I can find no conclusive evidence that it was even used as a skirmisher battalion, which, as Tom correctly points out, was intended to be its primary purpose.

Instead, it looks to me like the army didn't really know what to do with a "special" battalion, and the records indicate to me that it was used as a standard manuever battalion.

That all changed, of course, when the army was pulled into Vicksburg and the siege began. Both Union and Confederate records mention the "annoyance" (Union) or "deadly effect" (Confederate) -- take your choice -- of the battalion's sharpshooters in a "sniper" role.