I can get a worn 4" Ruger Service Six in .357 Mag for a very reasonable price. The lock-up and cylinder timing seems to be sound, it does not have excessive flame cutting at the forcing cone, etc. The barrel, however, seems quite smooth (although looking at my Ruger Security Six that is in good condition, the lands and grooves in the barrel are also not prominent).
If I buy it, it will be used for pin shooting at seven meters, requiring about an inch group at 7 m. My question, assuming that the barrel is quite worn, what effect will it have on grouping at 7 m? I shoot 180 gr copper metal jacket bullets at 1 000 ft/sec.