Gus Norcross, originally trained on National Match rifles and pistols by the National Guard Marksmanship Training Unit specializes in Garands, M14s and 1911s at his small shop on the coast of Maine. His website is www.angusarms.com. He will be offering gunsmithing tips and tricks on Fridays.
A complete accuracy job on a 1911 style pistol begins with a stripped frame and slide. Using feeler gauges, measurements are taken of horizontal and vertical movement with the slide in battery and recorded on a worksheet. The thickness of the slide rails behind the slide stop notch is also recorded. A special Starrett #207 micrometer (Brownell’s part #827-561-730) makes measuring the rails an easy task.
A pistol I just measured on the bench (Colt 1991A1) looks like this: Left and right rails are both .117″, horizontal play is .007″ and vertical is .006″. We want to reduce movement in to .001-.002″ in either direction.
Horizontal movement can be reduced by squeezing the slide. You need a large, stout vise and some form of medication for your nerves when using this method. Slide rails may crack or collapse. Ask me how I know. Risky. Slides are a relatively expensive component.
A safer method is to tighten the slide through peening the frame rails downward on to precision ground steel bars (Brownell’s part #080-745-000AH) with a small ball peen hammer. We do one rail at a time. The frame is held securely in a vise and a bar .001″-.002″ thicker than the slide rail is selected and inserted under the frame rail.
As the rail is peened metal is moved downward and outward. We only work the rail sections to the front and rear of the mag well, creating four points of contact. Peening the edges of the mag well risks pushing metal into it and creating problems with magazine fit.
Once the peened rail is evenly swaged on to the bar, it is removed and the frame rail is filed or machined back to its original width plus half the tolerance we are trying to remove.
Our Colt had a total frame rail width of .749″ and .007″ horizontal play, so we file it back to .752″ and add another .003″ to the total width when we peen the other rail, keeping the slide centered. The slide is lapped to the rails and sharp edges are deburred as necessary. Stainless steel pistols may be tougher to tighten due to the gumminess of those alloys.
Fitting a slide will have little effect on practical accuracy, but it should be the first step in an accurizing package when a match-grade barrel is fitted and maximum long range precision is required.