Reliable 338 ARC reloading data is provided directly by its creator, Hornady, which engineers distinct subsonic and supersonic load parameters specifically for the AR-15 platform.Published data normally includes specific bullet designs, velocity expectations, strict cartridge overall lengths, and dual-purpose pressure thresholds.Common bullet weights covered by published 338 ARC load data range from 170-grain supersonic hunting projectiles up to massive 307-grain subsonic bullets.Results naturally vary due to differing test barrel lengths, exact powder burn rates, brass case capacities, and the strict division between 30,000 PSI subsonic and 52,000 PSI supersonic limits.
338 ARC Reloading Data
| Bullet | Bullet Weight | Powder | Published Starting Load | Published Maximum Load | Published Velocity | Pressure (Max) | Primer & Case | Cartridge Overall Length (COL) | Barrel Length / Firearm | Source |
| Hornady SUB-X | 307 grain | Factory Proprietary | Not Listed | Not Listed | 1,050 fps | 30,000 PSI | Small Rifle / Hornady | 2.260″ | 16.00″ / AR-15 | Hornady |
| Hornady HP Match | 175 grain | Factory Proprietary | Not Listed | Not Listed | 2,075 fps | 52,000 PSI | Small Rifle / Hornady | 2.260″ | 16.00″ / AR-15 | Hornady |
| Hornady MonoFlex | 170 grain | Factory Proprietary | Not Listed | Not Listed | Not Listed | 52,000 PSI | Small Rifle / Hornady | 2.260″ | 16.00″ / AR-15 | Hornady |
| Hornady FTX | 215 grain | Factory Proprietary | Not Listed | Not Listed | Not Listed | 52,000 PSI | Small Rifle / Hornady | 2.260″ | 16.00″ / AR-15 | Hornady |
| Hornady FMJ | 285 grain | Factory Proprietary | Not Listed | Not Listed | Not Listed | 30,000 PSI | Small Rifle / Hornady | 2.260″ | 16.00″ / AR-15 | Hornady |
Understanding The 338 ARC Reloading Data
To safely develop a 338 ARC load recipe, handloaders must understand the specific variables that dictate this heavy-hitting AR-15 cartridge:
- Starting load: The minimum safe powder charge. Because the cartridge is so new, official starting charges are currently pending in major manuals, requiring reloaders to rely heavily on factory baseline velocities.
- Maximum published load: The absolute pressure ceiling. For the 338 ARC, this is strictly dictated by whether the load is subsonic or supersonic.
- Velocity: The speed of the bullet in feet per second (fps). The speed of sound is roughly 1,125 fps; Hornady intentionally caps subsonic loads at 1,050 fps to prevent a sonic crack.
- Pressure:The 338 ARC operates under two entirely separate pressure limits: 30,000 PSI for heavy subsonic loads, and 52,000 PSI for lighter supersonic loads.
- Bullet weight: The mass of the 0.338-inch projectile in grains.
- Powder: The specific propellant chemistry. The 338 ARC requires fast-burning magnum pistol or light rifle powders to achieve a complete burn in short barrels.
- Barrel length:Test barrels for the 338 ARC are typically 16 inches, though it performs exceptionally well in shorter SBR configurations.
- Firearm used for testing: Universal receiver test barrels or production AR-15 platforms utilizing a 6.5 Grendel Type 2 bolt face.
- Test conditions: Altitude, humidity, and temperature variables during pressure testing.
- Cartridge overall length (COL): The total length of the loaded round. Standard AR-15 magazines strictly restrict the COL to a maximum of 2.260 inches.
Different published sources and independent tests produce varying results because the cartridge uses a large .338 bore with very little powder capacity. Small changes in seating depth drastically alter internal case volume and chamber pressure.
338 ARC Bullet Weight Reloading Data
The 338 ARC was designed to offer massive projectile mass at short-to-moderate ranges.
- 170 grain to 175 grain: The standard weights for supersonic 338 ARC reloading data. Bullets like the 175-grain HP Match or 170-grain MonoFlex are driven to roughly 2,075 fps from a 16-inch barrel. They are highly effective for medium game hunting inside 200 yards.
- 215 grain:A mid-weight projectile utilized in Hornady’s FTX Black line, offering a balance of penetration and expansion.
- 285 grain: Supported by current published data in Hornady’s Frontier line. This heavy Full Metal Jacket (FMJ) bullet is primarily utilized for subsonic target practice.
- 307 grain: The flagship weight for the cartridge. The 307-grain Sub-X is designed specifically to expand at low subsonic velocities (down to 900 fps), providing massive terminal energy without breaking the sound barrier.
Do not assume heavy .338 Lapua Magnum bullets can be utilized. Extremely long, heavy .338 bullets (like 250-grain or 300-grain boat-tail match bullets) will seat too deeply into the short 338 ARC case, severely compressing the powder and creating dangerous overpressure.
338 ARC Powder Reloading Data
Because the 338 ARC uses the 6.5 Grendel as a parent case but opens the neck to .338, the powder capacity is extremely limited relative to the bore size. While proprietary powders are used in factory ammunition, independent handloaders developing a 338 ARC load recipe focus on fast-burning powders:
- Accurate 1680: Widely considered by independent AR-15 handloaders as one of the most optimized powders for cycling 300+ grain subsonic bullets.
- Hodgdon Lil’ Gun: Frequently cited for achieving high velocities with 100% powder burn in 16-inch or shorter barrels, producing very low standard deviations.
- Hodgdon H110 / Winchester 296: Excellent fast-burning choices for both heavy subsonic loads and lighter supersonic applications.
Never assume that a powder charge developed for a 300 Blackout can be directly copied into the 338 ARC. The internal case volumes and bore diameters are completely different.
338 ARC Bullet And Powder Combinations
The exact component combinations dictate both the safety and reliability of 338 ARC load development.
- Case capacity and seating depth: The blunt, heavy 307-grain projectiles take up significant space inside the case. Pushing a bullet just 0.020 inches deeper than the published COL significantly compresses the powder charge, spiking pressure.
- Primer: The cartridge requires Small Rifle primers. Magnum primers are frequently recommended by independent testers to reduce standard velocity deviations and ensure consistent ignition of densely packed ball powders.
- Bullet construction: Monolithic solid copper bullets (like the 170-grain MonoFlex) create more bore friction than standard lead-core bullets of identical weight, generating higher pressures faster.
- Firearm configuration:The 338 ARC uses a 6.5 Grendel Type 2 bolt (0.136-inch face depth).Because the bolt face is thinner than a standard 5.56 bolt, it is critical to stay strictly under the 52,000 PSI supersonic pressure limit to prevent shearing the AR-15 bolt lugs.
338 ARC Velocity From Published Data
Published 338 ARC velocity figures depend on the distinct factory load utilized.
| Bullet | Bullet Weight | Published Load | Muzzle Velocity | Barrel Length | Firearm | Source |
| Hornady SUB-X | 307 grain | Factory Subsonic | 1,050 fps | 16.00″ | AR-15 Platform | Hornady |
| Hornady HP Match | 175 grain | Factory Supersonic | 2,075 fps | 16.00″ | AR-15 Platform | Hornady |
Clearly distinguish between official factory velocities and independent chronograph testing. Going shorter than a 16-inch barrel will cost approximately 25-30 fps per inch for supersonic loads, though subsonic loads are tuned to stay near 1,050 fps regardless of barrel length.
338 ARC Reloading Data By Barrel Length
The 338 ARC was highly optimized for short-barreled rifles (SBRs) and suppressors.
Because subsonic loads utilize very fast-burning powders (like Lil’ Gun or 1680) that achieve a complete burn in under 10 inches, barrel length has a minimal impact on terminal subsonic velocity. A 307-grain bullet fired from a 10-inch SBR will perform remarkably similarly to one fired from a 16-inch rifle. However, shooters relying on the 175-grain supersonic load will experience a noticeable drop in speed and effective range when utilizing ultra-short barrels.
338 ARC Energy And Ballistics
The 338 ARC was purposefully engineered to deliver massive kinetic energy inside 200 yards. Using verified Hornady factory data from a 16-inch barrel:
- 175-grain HP Match (Supersonic):
- Muzzle velocity: 2,075 fps
- 200-yard energy: 1,115 ft-lbs
- 307-grain SUB-X (Subsonic):
- Muzzle velocity: 1,050 fps
- Muzzle energy: 752 ft-lbs
The massive 307-grain projectile delivers approximately 1.5 times the muzzle energy of a standard 220-grain 300 Blackout subsonic load (which typically generates around 480 to 500 ft-lbs).
Manufacturer Data vs Independent Testing
When researching a 338 ARC load data chart, handloaders will currently encounter:
- Manufacturer-published factory data:Officially pressure-tested by Hornady to guarantee loads stay safely under the 30,000 PSI (Subsonic) or 52,000 PSI (Supersonic) SAAMI thresholds.
- Independent chronograph testing: Velocities recorded by early adopters using powders like AA1680 or H110. This verifies bullet speed and AR-15 cycling but cannot verify internal chamber pressure.
Because official powder charge tables are still emerging, priority must always remain with Hornady’s published pressure limits and cartridge overall length specifications.
338 ARC Pressure And Safety
The most crucial safety aspect of 338 ARC reloading is understanding its dual-pressure nature.
Subsonic loads are capped at 30,000 PSI. This ensures the massive bullet moves slowly enough to avoid a sonic crack, while still generating enough gas volume to cycle an AR-15 bolt carrier group. Supersonic loads are pushed to 52,000 PSI. Reloaders must never attempt to push heavy 300+ grain bullets to supersonic pressures, as the limited case capacity will result in a catastrophic, firearm-destroying overpressure event.
Furthermore, the 338 ARC requires dedicated 6.5 Grendel/ARC magazines to feed correctly. The wider case shoulder prevents the rounds from stacking properly in standard 5.56 NATO magazines.
Best Sources For 338 ARC Reloading Data
The strongest and most authoritative sources for safe 338 ARC load development include:
- Hornady:As the original developer of the cartridge, Hornady provides the definitive baseline data, explicitly defining the 2.260″ COL and pressure limits. Comprehensive powder charges are expected in their upcoming reloading manual updates.
- Hodgdon Reloading Data Center: Continues to update their free online database with new ARC family data as the cartridges become widely adopted by handloaders.
- CMMG & Aero Precision:Leading manufacturers producing 338 ARC barrels and bolts, providing critical twist rate (1:8) and gas system compatibility data.
Common 338 ARC Reloading Data Questions
Where can I find 338 ARC reloading data?
Authoritative baseline specifications are published directly by Hornady, with comprehensive powder charge tables pending in upcoming editions of the Hornady Reloading Handbook.
What powders are used in published 338 ARC data?
Independent reloaders and ballistic testers commonly utilize fast-burning powders like Accurate 1680, Hodgdon Lil’ Gun, and H110 to mimic factory performance.
What bullet weights have 338 ARC reloading data?
Data focuses on lightweight 170-grain to 175-grain supersonic projectiles, and massive 285-grain to 307-grain subsonic bullets.
What is the best source for 338 ARC reloading data?
Hornady is the original developer of the 338 ARC and provides the most authoritative baseline data regarding pressure limits and velocity expectations.
Why does 338 ARC reloading data vary between sources?
Variations occur due to the massive discrepancy between 30,000 PSI subsonic data and 52,000 PSI supersonic data, alongside differences in case capacity and exact bullet bearing surfaces.
Does barrel length affect 338 ARC velocity?
Yes, for supersonic loads, you will lose roughly 25-30 fps per inch of barrel reduced.Subsonic loads are generally unaffected as they are specifically tuned to stay below 1,050 fps.
Can the same powder charge be used with a different bullet?
No. Different bullet profiles alter internal case capacity. Seating a long 300-grain bullet deeply into the case dramatically shifts chamber pressures.
What is the difference between starting and maximum published load data?
The starting load is the safe baseline for working up a new recipe. The maximum load is the highest pressure limit established safely by a ballistic laboratory.
Where can I find pressure-tested 338 ARC data?
Pressure-tested standards (30,000 PSI and 52,000 PSI) are established by SAAMI and published by Hornady.
Does Hodgdon publish 338 ARC reloading data?
Hodgdon manufactures the fast-burning powders (like Lil’ Gun and H110) ideal for the cartridge, and their online Data Center updates regularly as new SAAMI cartridges are standardized.
Does Hornady publish 338 ARC reloading data?
Yes. Hornady created the 338 ARC and publishes the most comprehensive factory velocity and pressure specifications available.
Does Nosler publish 338 ARC reloading data?
Nosler publishes generic .338 caliber bullet data, but dedicated AR-15 338 ARC data is best sourced directly from Hornady.
Does Alexander Arms publish 338 ARC data?
No. Alexander Arms developed the 6.5 Grendel and .50 Beowulf. The 338 ARC was developed by Hornady, which serves as the primary source for its data.