Designed to bridge the gap between 308 Winchester/7.62 NATO and 50 BMG, the 338 Lapua Magnum (8.6×70) has developed an impressive following with long range shooters. When I built mine, I settled on a 22″ barrel, which is short for this cartridge. Accuracy International does offer a 20″ barrel 338 Lapua from the factory, but you’ll notice most shooters running barrels from 27 to 30″ long.
The rifle was built with the following parts from Brownells (I will be covering its construction in another post):
- Deviant long action receiver (100-012-651)
- Shilen select .338 1:10 barrel blank (787-000-028)
- Timney 517 trigger (883-000-029)
- Surefire MB338SS03 muzzle brake adapter (152-000-051)
- Spuhr ISMS (100-011-207)
- Nightforce NXS 8-32×56 mil/mil scope (100-012-581)
After quite a bit of research I decided to try 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 (I don’t post complete load information, however, if you take a look at the powder companies data you’ll be headed in the right direction).
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|
I was shocked by how low the SDs were with Reloader 25. Unfortunately, the velocity wasn’t there. If I had a 26 or 27″ rifle, I would be exploring it further.
H1000 had low SDs, however, accuracy was poor.
US869 offered a shockingly accurate load, but it had minor pressure signs and large SD.
That leaves Retumbo (an elusive powder to buy lately). With relatively low SD, high velocities and good initial accuracy. None of the loads I tested exhibited pressure signs. Plus, they didn’t seem to be that hard on the brass. I was actually shocked I safely broke 2600 feet-per-second with any of the loads. Approaching 2800 feet-per-second with a 300 SMK from a 22″ barrel seemed like a dream. I guess dreams can come true.
For the phase of load development, I’ll be working up some more loads with Retumbo and posting the results.