The 1908 Olympic small-bore rifle title was decided at Bisley over rounds at 50 years and 100 yards. After the opening round at 50 yards, Carnell was in the joint fifth position but moved into the lead during the second phase at 100 yards, finishing one point ahead of Harold Humby, the half-way stage leader. Carnell finished with a total of 387 points out of a possible 400 and in view of this fine performance in the individual event, he was asked to compete in the team event, for which he had been named as reserve. Not wishing to deprive another marksman of the chance of Olympic competition, Carnell declined selection for the team event but despite his absence, Britain still won the gold medals by a comfortable margin. Both Arthur Carnell and his wife, who was also a champion shot, were members of the Mansfield (Highgate) Rifle Club.
Great Britain