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.
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:
- Deviant 338 Lapua Action (100-012-651)
- #7 Shilen select match barrel, .338 caliber 1 in 10 twist (787-000-028)
- 3/8″ high-speed steel turning took set (080-000-835)
- Viper’s Venom cutting oil (100-013-368)
- Badger FTE muzzle brake 5/8-24 (093-000-040)
- High-speed steel threading kit (080-000-839)
- Jewell HVR trigger (100-002-559)
- Brownells barrel vise (080-860-307)
- Brownells Remington 700 action wrench (080-800-700)
- 338 Lapua “go” and “no go” gauges (513-000-105) (513-000-104)
- AICS AX chassis 338 CIP (100-013-358)
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All lathe work was conducted on a Grizzly 4003G lathe.
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.
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.
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.
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|
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.
I am quite pleased with the rifle. I can’t wait to shoot it some more!
To build your custom 338 Lapua Magnum rifle, visit Brownells.
Thank you Camp-Site Sport Shop for handling the FFL transfer.