Do you know what a proper barrel fit looks like? Probably not. My answer is based on the abundance of information on the internet from "gunsmiths", many of which don't understand how the 1911 operates. During my time studying and building 1911 pistols with Bob Marvel, he drilled into my memory how important each part of the pistol was and how they work together. This post is meant to dispel myths and false information about barrel fit.
Yes, to have a pistol with maximum accuracy capability must have an extremely tight bushing to barrel fit AND bushing to slide fit. Bushing to slide fit should be tight enough that it requires taping into and out of place in the slide. The OD of the barrel and ID of the bushing must be fitted within tenths of a thousandth of an inch (.0002). If the OD of the barrel and ID of the bushing are fit with a thousandth (0.001) or more of tolerance, accuracy potential is lost.
But doesn't the tight bushing and to barrel tolerance cause the pistol to be less reliable? Not at all. It is more likely that the barrel legs are not correctly fit.
Speaking of leg fit, how do I know if my legs are fit correctly? Pretty easy, the barrel should touch the slide stop only on the flat of the leg in an area of approximately .080 to .090 thousandths of an inch. If the barrel legs are contacted at any other place other than the flats, it causes a circumstance called barrel bump. When barrel bump occurs, reliability and accuracy are adversely effected. Almost EVERY custom 1911 and factory 1911 have this issue. Another important part detail of leg fitting is leg bearing. Both legs MUST bear on the slide stop. No exceptions. 100 percent bearing on both legs is not necessary, but each must bear and preferably an equal amount on each leg.
For maximum accuracy the barrel hood must NOT touch on the sides. The hood MUST touch the breach face when in battery. When fitting the hood, a method of determining fit is by using a .001" feeler gauge and bushing the barrel into batter when the slide is off the frame. If the barrel presses into battery and holds the feeler gauge firmly in place, the hood length is good. This method allows the pistolsmith to know the hood will touch the breach when the pistol is assembled and in battery, but also has enough clearance during cycling that the barrel will drop free.
All the above work is pointless if the chamber is not cut to the proper depth. Many custom 1911 pistols are sent out without a properly chambered barrel. If the pistol is chambered in 9mm, I recommend getting the Marvel 9x19 reamer. It has modifications that allow better chambering and smother transition of the barrel from the lead to the lands and grooves.
On the business end of the barrel, the crown plays a crucial role in accuracy. If they crown isn't cut correctly, the pistol won't hold reliable groups. At all. I can almost guarantee that every pistol that has the flush cut and deep crown barrel cannot hold a decent group. If you have on and feel that I am wrong, please take a video of you shooting groups, preferably from a rest, at a distance no closer than 25 yards and post it here.
Tons of detail goes into correctly fitting a barrel. This is just a short and rundown of the highpoint of fitting and not an all inclusive lesson on fitting.