The Boers captured a staggering amount of British arms and equipment during the war (the boers usually released the thousands of POW's they took while the British deported theirs to Sir Lanka and sent their families to concentration camps). So that by the end of the war they were mainly using various types of Lee Enfields/Metfords.
The Lee performed better with the Boers than it did with the British. Even in the current British Army units constantly fuck with soldiers individual weapons, ridiculous cleaning regimes, using rifles as PT props, armorers that aren't really armorers fucking around trying to fix fault. I'm willing to bet circa 1900 it was even worse. There would be a regimental shooting team, but every other soldier would fire the bare mininum, and in the days before mandatory quals I suspect some could go years without firing a rifle.
During the first boer war, the boers picked up that the British were consistently shooting low, even though the British never did. There's also suspicians that the Zulus took far fewer casualties at Isandlewana that was supposed, because the Zulus closed on them too fast for them to adjust their sights (the lack of ammunition is a proven myth). The problems with individual marksmanship were amplified by officers insisting on controlling fire while not having the training to give a fire control order that was anything other than a range a general direction.
Anyway during the Boer war British marksmanship was consistently shit, blaming the lee enfield and the dastardly mausers which the boers had stockpiled was largely cope. At the end of the war large British forces were geting hammered by smaller boer forces using the same Lee enfields they were.