In Australia the .303 was very popular in the 1950's & 60's as a centerfire cartridge, since there was a plentiful supply of ex-military rifles & ammunition. Almost every farmer had a bolt action .22, a single barrel 12g shotgun and a Lee-Enfield .303 for the kangaroos & pigs.
As mentioned in earlier posts, the .303 Lee-Enfield is still shot regularly in 600 yard + matches. The current world record for aimed bolt-action fire was set in 1914 by a musketry instructor in the British Army - Sgt Instructor Snoxall, who placed 38 rounds into a 12 inch wide target at 300 yards in 60 seconds with a Lee-Enfield .303.
Billy Sing, an Australian Light Horse sniper during WW1 had 151 confirmed kills & an estimate of 300 overall kills with his Lee-Enfield .303 at ranges up to 1,000 yards.
If your .303 is in reasonable condition it shouldn't be a problem to hit a target at 100 yards.