Chambering a rifle barrel between centers

September 28, 2014 Bill Marr Gunsmithing 0

When you chamber (or fit) a barrel blank to a rifle you have to cut it on a lathe.  There are two basic ways to do this: one is to mount the barrel blank through the headstock, the other is to turn the barrel between centers.  The method a gunsmith uses is typically determined by his equipment.  If a headstock has a small through-spindle diameter, the through the headstock method will not work.  Likewise, if you are chambering a short blank, you will not be able to secure the muzzle end of the barrel on the back end of the headstock.  Certain lathes, and conditions, call for chambering between centers.

I chamber most of my barrels through the headstock of my lathe (check out the projects guns page).  Occasionally, I will chamber barrels between centers.  Current trends have most guys dialing the chamber end of the blank to within .0001″ and indexing the muzzle.  This is sometimes referred to as the Gritters method (Gordy Gritters is an outstanding gunsmith).  Some precision rifle builders look down on chambering between centers.   I don’t understand the hate.  If the Marine Corps Precision Weapons Shop and McMillan Custom Rifles both chamber between centers, how bad a method can it possibly be?

The barrel used in this post is a Shilen #7 contour Select Match .308 1:10 twist.  This barrel had previously been threaded and chambered for another rifle.  I mention this, because you may notice the pre-existing threads on the muzzle.

The action is a factory Remington 700 short action.  The bolt has been fluted by Kampfeld Custom.  The factory recoil lug has been replaced by a Hollands.

This post is designed to show the basic setup for chambering between centers.  For more specific information on how to chamber a barrel, see Chambering a Rifle Barrel.

Before starting work, I cut the old tenon off.  The plan is to end up with a 16.75″ barrel.

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Brownells provided the following tools for this project:

 

I take the time to gather the measurements I need for the barrel tenon and head space.
I take the time to gather the measurements I need for the barrel tenon and head space.
To start, I need to cut a tenon on the muzzle end of the barrel. This will be secured in the three jaw chuck. I use a piloted 60 degree center drill. This will cut a recess for the live center.
To start, I need to cut a tenon on the muzzle end of the barrel. This will be secured in the three jaw chuck. I use a piloted 60 degree center drill on the muzzle end of the barrel (not shown). This will cut a recess for the live center.
This is what the tenon looks like. It should be deep enough to remove any taper from the barrel and provide a small shoulder to snug up against the chuck jaws. Cutting a small band on the chamber side of the tenon will allow the barrel to be indicated concentric to the bore, rather than the outside of the barrel. Note the threads, these were cut when the barrel was installed on another rifle.
This is what the tenon looks like. It should be deep enough to remove any taper from the barrel and provide a small shoulder to snug up against the chuck jaws. Cutting a small band on the chamber side of the tenon will allow the barrel to be indicated concentric to the bore (rather than the outside of the barrel). Note the threads, these were cut when the barrel was installed on another rifle.
Now the barrel is swapped around. The tenon is inserted into the four jaw chuck and indicated. The live center is inserted into the chamber end.
Now the barrel is swapped around. The tenon is inserted into the four jaw chuck and indicated. The live center is inserted into the chamber end.

I am using a 4-jaw chuck in this post.  Using a collet system, if your lathe is equipped with one would work well.  Alternatively, fabricating a drive dog with a system holding the barrel against a dead center in the head stock would work.

I turn the tenon for the barrel to the diameter of the lug. I make a groove to provide relief for the action against the lug. A threading tool is installed. I am cutting 16 threads per inch.
I turn the tenon for the barrel to the diameter of the lug.  It is important to face the end of the barrel while it is set up.  This will ensure it is perpendicular to the threads.   I make a groove to provide relief for the action against the lug. A threading tool is installed. I am cutting 16 threads per inch.
The finished tenon. Looks pretty good.
The finished tenon. Looks pretty good.
I need to cut a bolt nose recess. Here I am using an undersized endmill to hog out most of the material.
Cutting the bolt nose recess. An undersized end mill is used to hog out most of the material.
A boring bar is used to finish cut the recess to the correct diameter and depth.
A boring bar is used to finish cut the recess to the correct diameter and depth.
Now is the time to check the action and bolt fit properly.
Now is the time to check that the action and bolt fit properly.
Time to cut the chamber. The reamer, with stop, is held in a Manson floating reamer holder. I am taking shallow cuts at 70 RPM with ample cutting fluid. No sense rushing here.
Time to cut the chamber. The reamer, with stop, is held in a Manson floating reamer holder. I am taking shallow cuts at 70 RPM with ample cutting fluid. No sense rushing here.
A close up view of the reamer stop. The stop allows depth of cut adjustment in .001" intervals.
A close up view of the reamer stop. The stop allows depth of cut adjustment in .001″ intervals.
The bolt should close on the go gauge. The handle stays open on the nogo.
The bolt should close on the go gauge. The handle stays open on the no-go.

A Badger FTE brake was mounted on the muzzle end of this barrel.  You can see how that was installed here:  Badger Ordnance FTE Brake Installation

Time to clean the barrel,  stamp the caliber and torque it onto the action.

Once the barrel has been cut and crowned, it is secured in a barrel vise and then an action wrench is used to torque the barrel into place.
Once the barrel has been cut and crowned, it is secured in a barrel vise and then an action wrench is used to torque the barrel into place.
This is what the rifle looks assembled. That is a 243 barrel in the front.
This is how the rifle looks assembled. That is a 243 barrel in the front.
Right side view, 16.75" 308 barrel installed.
Right side view, 16.75″ 308 barrel installed.

Does it shoot?  Not bad for the first 5-rounds downrange (below).

5 rounds 308 Winchester, 175 SMK .486" at 100 yards.
5 rounds 308 Winchester, 175 SMK .486″ at 100 yards.

 

 

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