Custom 338 Lapua Magnum Precision Rifle Build

Custom 338 Lapua Magnum Deviant Action 4

Since its introduction in 1989, the 338 Lapua Magnum has been a popular cartridge. The 338 Lapua was designed as a military cartridge to bridge the gap between the 308 Winchester/7.62 NATO and the .50 BMG cartridges. Capable of extreme accuracy at long range, rifles chambered in 338 Lapua Magnum are readily available from a number of manufacturers.

Left to right, 338 Lapua Magnum, 300 grain Sierra Matchking, 308 Winchester, 175 grain Sierra Matchking, 223 Remington, and 62 grain M855 projectile.

Unlike the .540″ bolt face found on most standard magnum cartridges, the 338 Lapua uses a Rigby .585″ bolt face. This is relevant when building a custom rifle since most custom guns are built on Remington 700 actions or clones of 700 actions. Since the 700 has a bolt diameter of .700″+/- the bolt nose becomes very thin. Additionally, the standard Remington 700 extractor cannot be used because the remaining wall of the bolt nose is too thin to support it (factory Remington 700s in 338 Lapua Magnum have a thin bolt nose and an M16 type extractor). A way around this is to use a custom action with a larger bolt diameter.

This rifle will be built with a Defiance Machine Deviant Action. The Defiance Action has a number of upgrades over a factory action, including an integral lug and rail, external bolt stop and larger .750″ bolt diameter.

We ordered the following parts from Brownells:

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

The Defiance Machine Deviant Lapua Magnum Action.

What does “dialing in” a barrel mean?

Without getting overly involved, the short answer: When custom rifle makers talk about “dialing in” or “indicating” a barrel, they are referring to the process used to ensure the bore of the barrel is running concentric to the lathe. The outside contour of the barrel, may or may not be concentric to the bore. Over the length of the barrel, the hole will move slightly. For most barrel makers, the industry standard of .001″ per inch of barrel length (.001″/inch) is generally agreed upon as a minimum; however, most makers exceed this. Even at .0005″/inch, the bore would move .015″ over the length of a 30″ barrel.

So why is this relevant?

I’ve used a number of different techniques to dial in the bores on my rifles. Depending on the job, I may do my work between centers, dial in just the chamber end (which is currently the most popular method because master gunsmith Gordy Gritters uses it) or both ends of the barrel.

When I chamber a barrel between centers, or dial both ends through a headstock, each end of the barrel is concentric, but the bore between the centers is most likely not. This is most relevant on the chamber end because the reamer may not be traveling concentric to the bore. Dialing in the chamber end, allows the reamer to follow the bore more precisely. The downside to this is the muzzle end will be off (and may be off quite a bit) and needs to be indexed with the high point at the 12 o’clock.

On this build, I’ll be dialing in both ends of the barrel- my preferred method lately.

We begin the process by dialing in the bore of the barrel blank. A grizzly rod with the appropriate bushing is used in conjunction with a dial indicator to ensure the bore in running true prior to starting any machine work.

The other end of our head stock has a four screw spider to center the other end of the barrel.

With the bore dialed in, I cut the end of the barrel true and cut the tenon to the appropriate length and diameter. — With the bore dialed in, I face the end of the barrel and cut the tenon to the appropriate length and diameter.

I make all my cuts with high-speed steel insert tooling and Viper’s Venom cutting oil. I make most of my cuts at a spindle speed of 360 RPM. I thread at 220 RPM.

I make a slight chamfer on the end of the barrel and make an undercut at the shoulder tenon junction. This ensures the barrel will be able to thread on tight against the action. — I make a slight chamfer on the end of the barrel and make an undercut at the shoulder tenon junction. This ensures the barrel will be able to thread on tightly against the action.

With a threading tool, I cut the thread to 16 teeth per inch. — With a high-speed steel insert threading tool, I cut the threads to 16 teeth per inch.

I coat the threads with a little bit of anti seize and check to make sure the barrel can thread on. — I coat the threads with a little bit of anti seize and check to make sure the action fits.

The bolt nose recess is cut with a speed steel insert boring bar. — The bolt nose recess is cut with a high-speed steel insert boring bar.

I test fit the bolt in the action to make sure the bolt fits inside the counterbore. — I test fit the bolt in the action to make sure the bolt fits inside the counter bore.

Deciding on the final barrel length and the type of brake was a bit of a challenge. So much so that I actually installed a Badger brake (on a 23″ barrel), coated the rifle and then decided to install a Surefire brake (on a 22″ barrel). Instead of documenting my indecisiveness, I will show how I installed the Surefire brake. Note the barrel has black Cerakote applied to it in the following pictures for the reasons I just stated.

I like to turn the tenon and threads for Surefire brakes between centers. I mount the barrel tenon in a four-jaw chuck and use a 60 degree center drill to run a counterbore in the muzzle end to allow the live center to be firmly placed in the barrel. Big guns get big brakes, the thread is 3/4″-24.

I use an high-speed steel threading tool to turn the threads at 24 threads per inch. — I use a high-speed steel threading tool to turn the threads at 24 threads per inch.

Time to clean up the crown. I secure the tenon in the steady rest and retract the live center. Note the end of the muzzle looks the way it does because I had removed a different brake. — Time to clean up the crown. I secure the tenon in the steady rest and retract the live center. Note: the end of the muzzle looks the way it does because I had removed a different brake.

A .420 crown tool held in a Manson floating reamer holder makes short work cutting the crown. — A .420″ crown tool held in a Manson floating reamer holder makes short work cutting the crown.

At this point the metal work on the rifle is done. All parts are degreased and assembled. I check headspace again when the rifle is fully assembled.

I coated the action and barrel in Cerakote Graphite Black. Since the bolt to action tolerances are fairly tight on a Deviant action, the bolt body is coated in Cerakote Micro Slick. Micro Slick is an air dry product that is much thinner than the heat cure Cerakote.

The Timney 517 trigger is installed and the barreled action is bolted into the AICS AX 2.0 chassis system.

My goal was to develop an accurate and relatively fast (2600 FPS+) load using the 300-grain Sierra Matchking (SMK). For comparison purposes, factory Lapua 300 grain ammunition is advertised at 2725 feet-per-second from a 27″ barrel.

I used four different powders: Reloader 25, H1000, Retumbo and US869.

Brass is new Lapua. Primers are Winchester Large Rifle Magnum (WLRM). Since my gun uses CIP length magazines, overall cartridge length is 3.708″, which is .020″ from the lands.

For each of the 14 loads posted below, I loaded 3 cartridges. A MagnetoSpeed barrel mounted chronograph was used to gather velocity information. All shooting was done prone, from a bipod, with a rear bag. The target distance was 100 yards.

Please note, I understand the limitations of 3-shot groups, however, during initial load development, they can lead you to an optimal load, without unnecessary barrel wear and component cost.

Load	Powder	Primer	Bullet	Velocity (FPS)	SD	Group (in)	Comments
1	Reloader 25	WLRM	300 SMK	2346	4.5	.859
2	Reloader 25	WLRM	300 SMK	2405	4.6	.988
3	Reloader 25	WLRM	300 SMK	2433	8.4	.748
4	Reloader 25	WLRM	300 SMK	2463	7.8	.365
5	Reloader 25	WLRM	300 SMK	2488	12.2	.823	MAX
6	H1000	WLRM	300 SMK	2607	8.5	1.340
7	H1000	WLRM	300 SMK	2641	14.2	1.009
8	H1000	WLRM	300 SMK	2673	4.0	.866
9	Retumbo	WLRM	300 SMK	2733	15.3	.570
10	Retumbo	WLRM	300 SMK	2764	7.4	.612
11	Retumbo	WLRM	300 SMK	2798	10.0	.346
12	US869	WLRM	300 SMK	2576	31.7	1.052
13	US869	WLRM	300 SMK	2678	32.1	.860
14	US869	WLRM	300 SMK	2719	9.6	.314	MAX

The heavy weight and effective muzzle brake make for manageable recoil. Shooting this rifle was far easier than I had imagined. Some of the loads I developed, particularly those with U869 and Reloader 25, made me laugh when I fired them- I think the brake was more violent than the bullet flying downrange.