1911 Pistol Modifications - Barrel Fit
by Dennis L. Schrieber, Pistolsmith
In any conversation about accuracy, barrels will always be a central topic. In a 1911, I have never found the type of material to make much difference, by this I mean steel or stainless. How the barrel is made and fitted is very important. A drop-in barrel can provide some gain in performance over the factory component. Remember that too fit in any gun these parts must have somewhat loose dimensions. Here is also where the lawyers get evolved with product liability, they must be safe in any firearm when installed be the amateur gunsmith. We must also consider the price to performance ratio. Drop-in barrels will generally be made from better materials, have a better finish and better dimensioning and tolerances than factory barrels but, will fall short in the area of fit to its oversize counterpart.
As I mentioned in the article on top end fit, accuracy depends on the barrel returning to the same relationship with the slide and frame each time. Too assure this, we utilize a series of triangles. There are four places that are used to form these triangles. The two most obvious are the barrel bushing and the upper locking lugs. As a rule-of-thumb, a one thousands of an inch (.001) of play, at any point, will increase the group size one inch at fifty yards. At the barrel bushing this slop must be considered between the bushing and the barrel and also between the bushing and the slide. Usually a bushing wrench is always required to remove a properly fit bushing. Another point to remember is that a barrel must tilt about 1 degree too unlock from the slide. This may not sound like much but, a standard national match bushing, when correctly fit, will require that its inside be modified to provide clearance. Also, the barrel will normally be turned down, just behind the fitting area of the bushing, to eliminate pinching and reduce drag. The spherical bushing made by Briley is my preference on match guns too eliminate these problems. The finger bushing that Colt introduced several years back was another attempt to address these issues. Although they did position the barrel well and did eliminate barrel pinch, the fingers were known to break off and jam the slide. Sometimes with a live round in the chamber.
The upper and lower locking lugs are primarily responsible for the safe lock-up of the firearm. The upper lugs should contact the slide at two and ten oclock only. And are the adjustment to center the firing pin on the primer. Only the rear lug actually locks the barrel up. The front lug is for safety and normally doesnt contact the slide. The lower lugs are what control the lock-up. They form a cam that rides on the slide stop pin, forcing the barrel up into the slide. Contrary too popular opinion, the link should be loose at lock-up. Its job is only too unlock the action. The use of a long link was not part of the logic of John Brownings design. In a target guns the lower lugs are cut with a lug cutter, hand filed and then lapped too achieve a smooth and tight fit. A slide stop pin is then cut to the correct diameter and also lapped in.
The fit point that is usually forgotten is the barrel hood. The hood should have some clearance on each side and have a lap fit on the end against the breech face. The hood will provide another point for our series of triangles and establish an stable reference for head spacing the chamber.
By using the six anchor points: the bushing, the barrel hood, and two points each on the upper and lower lugs we form eight triangles to firmly lock-up the barrel. Each of these points come oversize on a match barrel. Each can then be hand fit and lapped. The last step would be to ream the chamber to get the right head space and obtain the correct lead into the rifling.
If all this sounds like a lot of work, and it is but, it can be some of the most productive work that can be commissioned. A barrel should however, only be fitted after the slide and frame are mated. So, keep the shooting fun and safe and visit your favorite pistolsmith. All questions and comments should be directed to Dennis L. Schrieber, Burnt Mill Smithing , www.burntmill.com or e-mail firstname.lastname@example.org