February 08, 2013
The most critical component of a 1911 accuracy job is the barrel. If the barrel doesn't lock up into battery exactly the same way every time, accuracy will suffer. Factory barrels are manufactured to minimize or eliminate hand fitting and are generally referred to as "drop-in."
True match barrels must be hand fitted to the individual pistol and are manufactured oversized for a "gunsmith" fit. The pistolsmith will be required to remove material from the barrel hood and bottom lugs to achieve proper lockup. In this first article in our barrel-fitting series, we will cover the hood.
The Kart .45 ACP barrel we will fit to our pistol is one of the best quality tubes available. I have fitted dozens of them over the past few decades and I have never been disappointed by their accuracy. Machined from a forging, the bore is mirror polished for excellent performance with the lead semi-wadcutters favored by many bullseye shooters.
The barrel hood should fit into the slot above the breech face in the slide but we don't want the sides to make contact. A few thousandths clearance on each side is fine. Measuring the slide with dial calipers shows the width of the slot is .442 inches. The hood width of the Kart barrel is .451 inches, so some material will have to be removed from each side. Using a safe sided pillar file, carefully reduce the hood width until the barrel will drop into the slide and touch the breech face.
When test fitting the barrel, I use a Kart bench bushing and a barrel alignment block to keep it aligned with the slide.
Now that the hood width is set, adjust the length. You will note that when you test fit the barrel it won't go far enough to the rear for the top lugs to lock into the slide. The hood length of the new barrel is 1.33 inches and the recess in the slide where it fits is 1.314 inches, so you will need to remove .016 inches of material from the end of the hood to allow lockup and touch the breech face evenly without binding.
I use a lathe for shortening the end of the hood because it's quick and easy to keep my cuts square, but careful filing will achieve the same result. Final fitting involves lapping compound and tapping the barrel in and out of lockup until full contact is achieved.
Be advised that some breechfaces are not square, so the shape of the barrel hood must be adjusted accordingly.
When the hood is properly fitted, the barrel will lock up into the slide with finger pressure with clearance on the sides and light contact at the rear. In Part 2 of this series (next Friday), I'll fit the bottom lugs.
Here are the tools of the trade for efficient and accurate 1911 barrel fitting: a Kart bench bushing, barrel alignment block, pillar file and digital caliper.
As supplied from Kart, the barrel hood is too wide to enter the barrel slot. This is intentional to allow the pistolsmith to fit it accurately to any slide.
Narrowing the Hood
The hood is narrowed with a safe sided pillar file. As the name implies, a safe-sided file has no teeth on the sides to prevent marring the workpiece.
The barrel alignment block and bushing are used when test fitting the barrel. The bench bushing's a lot easier to install and remove repeatedly.
Measuring the barrel hood length. Norcross says you can't assume the breechface is square; the hood may have to be filed at an angle for best fit.
Shortening the Hood
Norcross uses a lathe when shortening the hood, but says the job can be done with a file if you are patient and careful. A close fit will pay off in accuracy.