Re-chambering a barrel: 243 Winchester to 6×47 Lapua

measuring dimensions for barrel tenon — I take the time to gather the measurements I need for the barrel tenon and head space.

Often high-volume shooters will re-chamber or set back a used barrel. Most do it to change calibers or give a worn throat new life. You need to have enough barrel shank to set back a barrel and re-chamber it. This is one of the advantages of a heavy barrel contour, there is plenty of material to work with if you want to change your configuration.

Excited by the arrival of a new 6×47 Lapua reamer, once again, I decided that 243 Winchester wasn’t the cartridge for me (I do this every five years or so with 243- I do save my brass for my next 243 phase). The article I wrote about this custom Remington 700 rifle, Remington 700 Rebuild: Transforming a Factory 700 AAC Rifle to a Custom Precision Rifle, provides an overview of how I built it. This poor rifle has been through a number of modifications. At one point it had a 28″ tube, then a 26″, a 26″ with brake, 24″, 24″ with brake and a finally I fluted it on milling machine (don’t get bored when you own a lathe and a mill). Now it’s time to become a 22.5″ 6×47 Lapua.

Brownells provided the following tools and supplies for this project:

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All lathe work was conducted on a Grizzly 4003G lathe.

After I make sure the rifle is safe and empty, I remove the barreled action from the chassis and unscrew the barrel.

I take the time to gather the measurements I need for the barrel tenon and head space. These are critical dimensions, measure incorrectly and you risk injury or death.

A word of caution if you are planning on re-chambering a barrel. Make sure you remove enough of the old chamber so that your new chamber fully supports the new cartridge. There are a number of pictures on the internet of horrible failures that have occurred because of poor planning or lack of understanding of the process. For instance, turning a 221 Fireball to a 223 Remington is fairly straight forward since the new cartridge is larger than the original. In a case like this, a 243 Winchester is larger than a 6×47 Lapua, so it is possible to not remove enough of the original chamber and create an unsafe condition. Additionally, making and measuring a chamber cast before you fire the rifle is ideal.

Looking at the cartridge drawings for the 243 Winchester and 6x47 Lapua, I decided that I could cut off the existing barrel tenon and use the 6x47 Lapua reamer to remove the remainder of the old chamber. — Looking at the cartridge drawings for the 243 Winchester and 6×47 Lapua, I decided that I could cut off the existing barrel tenon and use the 6×47 Lapua reamer to remove the remainder of the old chamber.

Yes, I use a cold saw to cut off barrels. If you are unfamiliar with cold saws, they use a slow moving carbide toothed blade (note the small shavings in the background of the picture). Unlike an abrasive saw, they do not add much heat to the barrel, plus they are faster and smaller than a band saw. A few reputable rifle builders shy away from parting tools to cut off barrels because they feel it may induce too much stress. Since my band saw is under a pile of other tools (limited space), I used to use a hacksaw, but settled on the cold saw. I haven’t noticed any negative effects on accuracy in the finished barrel.

I mount the barrel in the head stock of my lathe. and dial in the chamber using a .0005" indicator, followed by a .0001" indicator. — I mount the barrel in the head stock of my lathe. and dial in the barrel concentric to the chamber using a .0005″ indicator, followed by a .0001″ indicator.

I used a high-speed steel profile tool to square the end of the barrel and cut the tenon. A 60-degree threading tool is used to cut the threads.

My apologies, I forgot to take pictures of the tenon and thread cuts. Please refer to Chambering a Rifle Barrel for more detailed photos and information.

A boring bar is used to cut the bolt nose recess. Since this barrel has been previously chambered, a piloted .705" counter bore would not work since the pilot wouldn't have anything to guide it. — A boring bar is used to cut the bolt nose recess. Since this barrel has been previously chambered, a piloted .705″ counter bore would not work since the pilot wouldn’t have anything to guide it.

I cut the chamber using a floating reamer holder and a reamer stop. I am using my newly built chamber flush system to push pressurized oil through the bore. — I cut the chamber using a floating reamer holder and a reamer stop. I am using my newly built chamber flush system to push pressurized oil through the bore (I’ll be posting an article on how I made it shortly).

I use this adapter made by GTR tooling to attach the power flush system to the barrel.

The bolt closes on the go. It stays open on the nogo gauge. Success! — The bolt closes on the go and it stays open on the no go gauge. Success!

I use Viper’s Venom cutting oil when I cut my tenon and threads. I turn my tenon at 360 RPM and thread at 220 RPM. The power flush chambering system I built uses Do-Drill cutting oil, using it; I cut this chamber at 360 RPM.

Finally I reverse the barrel in the headstock and run a .420 crown tool on the muzzle to clean things up.

Time to degrease the rifle, hit it with a coat of paint and head to the range. I am lucky enough to have a friend who is a talented painter. He was kind enough to spray the rifle with a coat of KG.

I put the action back in the AICS AX stock with a Jewel HVR trigger and Nightforce F1 3.5-15 Mil/Mil scope. I worked up eight different loads (three rounds of each) for load development using the Berger 108 grain BTHP, Lapua brass (6.5×47 Lapua necked down), CCI 450 primer and H4350 powder.

I worked up 8 loads with a Berger 108 BTHP, H4350, Lapua brass and a CCI 450 primer.

Here at the eight, 3-shot groups I fired at 100 yards during initial load development. Average .608, best .408", — Here are the eight, 3-shot groups I fired at 100 yards during initial load development.

6×47 Lapua is an interesting cartridge and I will write more about it later. Brass is easily formed by necking down 6.5×47 Lapua brass; which, if you have a 6.5×47 Lapua, is readily available (the 6×47 Lapua does seem redundant if you already own a 6.5×47 Lapua). You don’t have to fire form like a 6mm Dasher, plus you can feed from an unmodified magazine easily, unlike the 6mm BR or Dasher.

My load development groups were promising, but not the sub .200s I imagined. .512″, .548″, .563″, .701″, .408″, .865″, .488″ and .807″. I may do some load development with RL17 and see if anything improves. The .408″ group had a muzzle velocity of 2873 feet-per-second with a SD of 6.5 which isn’t too shabby. Still, I was hoping for better. Maybe it’s time for a 21″ 6mm Dasher?