I am asked often what are the benefits of having a gunsmith fit a barrel. This description will be somewhat over simplified but the answer of why it’s done will remain the same.
We have to understand what constitutes an accurate gun? Accuracy is achieved through repeatability. Factory fit barrels have loose tolerances so they can be dropped in to and will fit any factory gun the manufacturer is assembling. Those loose tolerances also allow barrel movement in the slide. This movement means that every time the slide returns to battery (or lock up) the barrel is not in the same orientation to the slide and therefore the sights each time. This means that the slight variation in barrel placement will show on the target.
This is where a gunsmith fit barrel and bushing comes into play. A gunsmith fit barrel and bushing is fit to the exact measurements of the gun its being fitted to thus creating a tight lock up each time the gun returns to battery. This repeatability creates accuracy. A properly fit barrel by a gunsmith should have a tight lock up as it enters battery with 3 points of contact. The words “tight tolerances” or “tight fitting” brings up a myth that is constantly regurgitated over the internet and that is that tight tolerances equates to less reliable.
“But tight tolerances create a gun that will not be reliable once it gets dirty.” The thought process is that tight tolerances or a tight fit and dirt create a gummy situation and foul up the works. This is purely myth and an incorrect statement. If a gun is built properly by a gunsmith with tight tolerances those tolerances themselves are what create a more reliable gun. Dirt can’t get into those areas because of the tighter tolerances themselves helping to create a very reliable and more accurate 1911.