This is my second installment of the custom 7mm Rem Mag Hunting Rifle post. As a quick recap, in my first post, Building a custom 7mm Rem Mag Hunting Rifle- Part 1, I gave a brief overview of the project background, removed the stock barrel from the action, trued the action and bolt face. The action is ready for a barrel. In this post I’ll cover threading and chambering the match barrel blank.
Before we get back to work, let’s take a look at the following disclaimer.
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As a reminder the action and bolt from the original stock Remington 700 rifle. In this series we are fitting a new stainless steel match grade barrel onto it, installing a blended brake, installing a match trigger, then placing it all in an MDT chassis.
I ordered the following parts from Brownells for this build:
- Brownells action wrench
- Farrell barrel vise
- Manson floating reamer
- Manson Chamber reamer
- Depth micrometer
- Viper’s Venom Cutting Oil
- Manson Headspace gauge
This is the last image from the first post. The bolt and action are ready for a new barrel.
To machine a blank, you need a metal lathe. This is my lathe when it was new, it is way dirtier now! It is a Precision Matthews PM-1440GT. I’ve found it does everything I could ask of it exceptionally well.
There are many opinions when it comes to barrel selection and machining methods. Each has its own strengths. The more I do this, the more I feel open to different ideas for different products and applications.
Let’s start by looking at perceptions of barrel quality. There are some excellent barrel manufacturers out there. Many shooters have a brand preference. I don’t. I’ve found that premium barrels all seem to be of good quality, and historically, I’ve found them to perform roughly the same. I’ll use Bartlein, Krieger, Rock, Hart, Shilen and Douglas interchangeably. My favorite barrel is the one that is in stock- period. If it matches the profile, caliber and twist rate I need and it is in stock, I buy it!
Enough barrel drama. Let’s look at what we have here, it is a Shilen #3 (sporter contour) match stainless steel barrel. It is roughly the same profile as the barrel that was on the gun from the factory- this is in keeping with the hunting rifle philosophy. While I usually machine tubes that look like truck axles; this one is sleek and smooth with an attractive contour forward of the breech end.
I always start working on barrels by dialing in the barrel concentric to the lathe on the outside diameter. I make a facing pass, then I insert a ground rod and dial in the barrel off the bore.
Once the barrel is dialed in I start cutting the tenon for the threads and recoil lug. I like to use a 35 degree profile tool to make the cut. I frequently check the diameter to make sure I don’t cut it too small. The threads and shoulder that hold the recoil lug need to be precise.
When the tenon is the correct diameter the recoil lug will slide over it with a slight drag. This is a 17-4 PH recoil lug that I manufactured myself.
With the shoulder sized for the recoil lug, I now prep it to machine the threads. In this case, I coated the tenon in red layout fluid. After the fluid dried I make a slight chamfer on the back end of the tenon and make a groove where the threads end and the recoil lug begins.
I cut the threads with a high-speed steel insert tool.
As the threads begin to form I take smaller and smaller passes to ensure the tightest possible fit with the receiver threads.
Remington 700 style actions and clones require a counterbore that is known as the bolt nose recess. This can be cut a number of different ways. Perhaps the easiest to use is a piloted form tool. The tool is held in a Manson floating reamer holder.
The best tool to check the depth of cut for the bolt nose recess is a depth micrometer. Normally these cuts are run .150″ deep. After I reach the depth I calculated, I check the action and bolt to make sure everything fits.
To cut the chamber I am using a Manson floating reamer holder. I clean the reamer and apply a liberal coat of Viper’s Venom cutting oil. I insert the reamer into the barrel, start the lathe and apply light pressure with the quill. Once I make a cut, I stop the spindle, retract the reamer, clean it off and repeat the process.
Since this cartridge is a belted magnum, the headspace gauge looks different than one you would find for a standard bottleneck cartridge. The headspace is determined by the rear cut for the belt. The downside of these gauge is you need to be careful, the hardened steel can create a burr at the cartridge body belt junction that needs to be polished out.
As I cut the chamber, I periodically thread the action in place with the headspace gauge. Since the chamber isn’t deep enough, there will be a small gap in front of the receiver. I measure this gap with a set of feeler gauges. I then cut half the depth I measured to prevent making too deep a cut in one pass.
When the chamber is cut to the correct depth, the bolt will close on the go gauge, and remain open on the no-go gauge (above).
The final step in the chambering process is to chamfer the outside edge of the counterbore.
Success! In the next post, we’ll finish the rifle up and install an MDT chassis.