If you had a choice for "sniper" work in the WBTS it would have to be the British made "Whitworth" rifle.
These were the most accurate long range rifle of the day. There sights were graduated out to 1000 yards. Some of them were fitted with primitive
telescopic sites. Yankee general John Sedgwick's last words (and my all time most favorite "last words"

were "they couldn't hit an elephant at this dis.........) Before the word distance was completely spoken he was hit in the head from a range of 800 yards. He was shot with a Whitworth rifle.
Second choice would have to be the British Enfield (sites graduated to 900 yards) Or perhaps some form of civilian target rifle.