Building a 300 Winchester Magnum Precision Rifle

Accurate, flat shooting and hard hitting!

Custom 300 Winchester Magnum equipped with 5-25 ATACR scope, Spuhr ISMS, AICS AX 2.0 and a Sierra 7 bipod.

I am a huge 300 Winchester Magnum fan.  I took a hacksaw and Sawzall to one in 300 Winchester Magnum: How Does Barrel Length Change Velocity- A 16″ 300 Win Mag?  And if that wasn’t ridiculous enough, I went and installed a brake on the gun for Does size matter? Custom Remington 700 16.5″ 300 Winchester Magnum follow up (FYI, my teeth and head still hurt from that one).

Sure, you can get similar external ballistics in a light recoiling 6mm or 6.5mm cartridge, but nothing smacks steel the way a big .30 caliber rifle does.  It’s in use by the U.S. Military (cool) and with the right load, it can rival the 338 Lapua Magnum at long range.  Reloading components, including quality Norma brass, factory hunting and match grade ammunition are readily available.  While it will pelt the shooter when chambered in a 6 pound hunting rifle, in a heavy rifle, recoil is manageable.

I ordered the following items from Brownells:

Bartlein Barrels supplied a tight-bore barrel for this project.  Bartlein’s 30 caliber tight-bore barrels have a bore diameter of .298-.299″ (ours is .299″), versus .300″ in a standard bore.  The groove diameter is similar, .3065-.3080″in the tight-bore .30 caliber, versus .308″ in the standard.  Tight-bore barrels are very popular in Palma matches, with shooters often reporting increased velocity over a standard bore diameter.

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The use of a custom action and chassis system greatly simplifies construction of this rifle.  If this was a factory Remington 700 action, I would blueprint the action (article: Blueprinting a Remington 700 Action) and install an external bolt stop.  Neither of these operations are required with a precision action like this.  Likewise, if I were using a fiberglass stock, such as a McMillan A5, I would be have to bed the barreled action into it.  With the AICS AX 2.0 chassis, this isn’t required.

Bartlein stainless steel M40 contour barrel with a 1-10 twist.

Bartlein stainless steel M40 contour barrel with a 1-10 twist.  Note the .299″ bore diameter and .308″ groove diameter.

The bore is dialed in on the chamber end with a Gritters-style rod.

The bore is dialed in on the chamber end with a Gritters-style rod.

The muzzle end of the barrel is secured in a spider on the back end of the spindle.

The muzzle end of the barrel is secured in a spider on the back end of the spindle.

I’ve mentioned this elsewhere, but it bears repeating.  I’ve chambered barrels many ways, and I think each system has its advantages and disadvantages .  Currently, I dial in both ends of the barrel through the head stock of the lathe. Without actually trying a few different methods, don’t believe that one way is superior purely because someone put it in a video.  Actually try different methods and see what works for you.

I turn the barrel at 360 RPM, thread at 220 RPM and ream the chamber at 70 RPM.  My preferred lubricant is Viper’s Venom cutting oil.

I cut the tenon to accept the recoil lug.

I cut the tenon to accept the recoil lug.

A relief cut is made between the tenon and the threads.

A relief cut is made between the tenon and the threads.

A sharp high-speed steel threading tool is used to cut the threads.  I am using Viper's Venom as a lubricant.

A sharp high-speed steel threading tool is used to cut the threads. I am using Viper’s Venom as a lubricant.

The completed barrel tenon.

The completed barrel tenon.

A quick test fit of the action ensures the recoil lug is tight against the tenon shoulder.

A quick test fit of the action ensures the recoil lug is tight against the tenon shoulder.

A high-speed steel boring bar is used to cut the bolt nose recess.

A high-speed steel boring bar is used to cut the bolt nose recess.

Finished bolt nose recess.

Finished bolt nose recess.

The bolt nose, bolt nose recess fit.

The bolt nose, bolt nose recess fit.

The reamer is secured in a floating reamer holder and is equipped with an adjustable reamer stop.

The reamer is secured in a floating reamer holder and is equipped with an adjustable reamer stop.

I chambered this barrel before I built my pressurized flush system.  I take light cuts at 70 RPM, stopping the lathe, retracting the reamer, cleaning and re-lubricating it every .025″ or so.   I’ve tried pre-drilling chambers, and running a boring bar to remove material and it works well, but, I wasn’t in a rush.

When the chamber is cut correctly the bolt will close on a "go" gauge and stay open on a "no go" gauge.

When the chamber is cut correctly, the bolt will close on a “go” gauge and stay open on a “no go” gauge.

The barrel is revered in the headstock and the muzzle is dialed in.

The barrel is reversed in the headstock and the muzzle is dialed in. The final barrel length is 24″.

I cut the tenon for the Badger brake as specified.

I cut the tenon for the Badger brake as specified.

I use a threading tool to cut the threads for the brake.

I use a threading tool to cut the threads for the brake.

A #3 piloted .420" target crown tool is secured in a reamer holder to crown the muzzle.

A #3 piloted .420″ target crown tool is secured in a reamer holder to crown the muzzle.

The finish crown looks great!

The finish crown looks great!

Finally the brake is installed on the end of the barrel.  A boring bar is used to open the brake to .020" over bore diameter.

Finally, the brake is installed on the end of the barrel. A boring bar is used to open the brake to .020″ over bore diameter.

Off to paint- in this case; Cerakote, graphite black.  An overview of how I coat my rifles can be found here, Cerakote firearm refinishing.

I selected the excellent Jewel HVR trigger for this rifle.  The Jewel is a very nice target trigger.  It does have a lot of screws and e-clips on it: I do not recommend it for heavy field use.

Since the rifle is sitting in an Accuracy International AICS AX 2.0 chassis, the stock work is completed once the barreled action is bolted in.    The optic is a Nightforce ATACR 5-25 Mil/Mil SFP scope mounted in a Spuhr ISMS.

Final assembly parts:

Custom 300 Winchester Magnum.

Custom 300 Winchester Magnum.

You maybe wondering about the Aimpoint T1 red dot sight on the Spuhr ISMS mount: it’s there to quickly find targets when the ATACRs magnification is dialed up (narrow field of view).

This is a pretty mean looking rifle!

This is a pretty mean looking rifle!

For initial load development, I worked up some loads with virgin Norma brass, H1000 powder, WLRM primers and the 208 A-Max. All shooting was done prone, from a bipod with a rear bag.

Load Bullet Powder MV FPS SD Shots Distance (yards) Size (inches)
1 208 A-Max H1000 2628 8.5 3 100 .421
2 208 A-Max H1000 2672 16.3 3 100 .538
3 208 A-Max H1000 2714 15.8 3 100 .412
4 208 A-Max H1000 2735 14.1 3 100 .897
5 208 A-Max H1000 2753 17.6 5 100 .402
Fed 190 Gold Medal 190 SMK 2908 16.1 5 100 .999

For what it’s worth, in my mind, I don’t weigh 3-round groups as heavily as 5-round groups.  I think they are functional for load development and determining if a rifle can shoot: however, I try to shoot 5 or 10-round groups as load development progresses to fully evaluate a rifle and cartridge combination.

The rifle, as shown above, weighs 18.14 pounds: Yikes!  The up side to big and heavy, is very manageable recoil in a belted magnum.

Best group of the day!  Virgin Norma brass, WLR primer, H1000 powder and 208 A-Max.  .402" at 100 yards.

Best group of the day! Virgin Norma brass, WLR primer, H1000 powder and 208 A-Max. .402″ at 100 yards.

Custom 300 Winchester Magnum equipped with 5-25 ATACR scope, Spuhr ISMS, AICS AX 2.0 and a Sierra 7 bipod.

Custom 300 Winchester Magnum equipped with 5-25 ATACR scope, Spuhr ISMS, AICS AX 2.0 and a Sierra 7 bipod.

I am quite pleased with the initial results.  I’ve done further testing and load development with the 210 SMK and will be posting about it soon.