Sporter contour rifle barrels have a radius cut by the shank (“E” in the diagram below). This is different from straight tapered barrels typically encountered on match rifles. Sporter contours are frequently used on hunting rifles where weight savings is a primary concern. The radius cut allows a great amount of material to be removed as opposed to a straight taper.
For comparison purposes, the table below from Brownells, lists the profiles and weights of the Shilen barrels they sell.
Note that profiles #1-#5 are sporter contours and profiles #6-#9 are straight tapers. The heaviest sporter contour typically encountered is the Factory Remington 700 Varmint or Sendero profile, and is not shown on the table above.
In this post I’ll be turning down a Green Mountain Barrels chrome moly blank to a (slightly modified) Remington Varmint Contour. The barrel will be used for a Remington 700 chambered in 7.62x39mm Russian, so I purchased one of Green Mountain’s .308″ bore, .310″ groove, 1:9.5 twist barrel blanks.
I ordered the following items from Brownells for this project:
All lathe work is conducted on a Grizzly gunsmith’s lathe.
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The blank is 1.375″ in diameter and 24″ long. Quite a heavy and impressive piece of steel.
The blank is mounted in a four jaw chuck and indicated to the bore.
A piloted 60 degree center drill is used to form a mating surface for the live center.
Note the 60 degree counterbore left by the center drill.
The barrel is now mounted between centers. I am looking for a finished barrel length of 16″ long, so I will be profiling 17″ of the blank. I will be using the rest of the barrel for a barrel length and velocity experiment; this excess material is in the headstock. The live center in the tailstock supports the chamber end of the blank.
I don’t work on chrome moly barrel as much as I work on stainless. As any machinist will tell you, speeds and feeds are key when machining. On this pass, I was experimenting with spindle speed. On the left the spindle speed was 220 RPM, on the right 360 RPM, all other settings were the same. Note the superior finish on the right side of the cut.
A factory Remington Varmint contour barrel has a slight taper on the tube. It measures .950″ in front of the shank, and .850″ at 26″. In this case, I’ll be cutting the entire barrel forward of the shank, .950″. I like to take a heavy pass, .040-.050″ at a time. Since I don’t have a lot of distance between centers, I didn’t need a steady or follow rest to get decent results. I’m cutting from left to right, towards the tail stock. This is because I don’t have a shoulder to prevent the barrel from sliding into the headstock.
All the turning makes for an impressive pile of shavings!
To determine the dimensions for the shank, I measure a barrel that I’d like to copy. This is a Bartlein with a Rem Varmint profile from another project. I mark the barrel in .100″ increments forward for the straight shank. I then record the measurements.
The measurements allow me to formulate a cut list needed to duplicate the profile. In this case, the list shows how far in I need to cut from the outside diameter of the blank. The number in the left column indicates how far from the shank I need to stop the cut. For instance, 1.5 indicates I need to take a cut .088″ deeper than the shank and stop 1.500″ from the beginning of the shank.
This is what the barrel looks like after the series of step cuts.
Another view of the step cuts. The black line indicates the end of the straight part of the shank.
A lathe file allows me to smooth out the profile.
This is the muzzle section of the barrel that was held in the chuck when the profile was turned. As stated earlier, I’d normally just chop it off, but I want to get some barrel length and velocity data with it. Before leaving the lathe, I’ll turn it down closer to the finished diameter of the barrel.
The barrel when it leaves the lathe.
The barrel is mounted in a barrel spinner. The barrel spinner supports the barrel between two ball bearings with a set of nylon centers. You can make or buy a barrel spinner, this one is a Clymer I ordered from Brownells.
The barrel is held in the spinner and run against a belt grinder. I start at 120 grit and gradually move up to 240, 320 and 400 grit belts.
My left hand is used to slow down the rotation of the barrel as it is held in the spinner.
The finish barrel barrel looks pretty sharp. A big change from when we started.
A view of the barrel installed on a Remington 700 chambered in 7.62×39!
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