338 ARC barrel length matters less than with many rifle cartridges, because the cartridge is made for subsonic shooting and a subsonic load is capped by the speed of sound, not by the barrel. In Chattahoochee Munitions testing, 338 ARC powder use is largely complete around 12 inches. Chattahoochee Munitions manufactures complete 338 ARC firearms in six barrel lengths: 8, 12.5 and 16 inches on the CM7S bolt action, and 8.5, 10.5 and 16 inches on the CM15 AR15.
338 ARC Barrel Length Options
| Firearm | Barrel | Twist | Overall length | Weight |
|---|---|---|---|---|
| CM7S bolt action | 8 inch | 1:5 | 20.5 to 28.0 inch | 5 lb 12 oz |
| CM7S bolt action | 12.5 inch | 1:6 | 26.0 to 32.5 inch | 6 lb 6 oz |
| CM7S bolt action | 16 inch | 1:6 | 28.5 to 36.0 inch | 7 lb 4 oz |
| CM15 AR15 | 8.5 inch | 1:5 | 24.54 to 27.04 inch | 5 lb 14 oz |
| CM15 AR15 | 10.5 inch | 1:5 | 26.54 to 29.04 inch | 6 lb 10 oz |
| CM15 AR15 | 16 inch | 1:8 | 33.25 to 36.5 inch | 6 lb 10 oz |
Weights are the firearm with an unloaded magazine and no accessories. Every barrel is 416R stainless with an E100 Blackout Cerakote finish and 5/8×24 muzzle threads; CM7S barrels come from Mos-Tek with 5R rifling.
Why Subsonic 338 ARC Works in Short Barrels
A subsonic bullet has to stay below the speed of sound, roughly 1,100 to 1,125 fps at sea level. Hornady rates its 307 gr Sub-X at 1,050 fps from a 16-inch barrel, already close to that limit, so a longer barrel has little room to add useful velocity. Cut the barrel shorter and the subsonic load gives up far less than a supersonic load would. That is why short-barrel subsonic is the core of the Chattahoochee Munitions 338 ARC lineup.
Where 338 ARC Powder Use Finishes
338 ARC barrel length and velocity are linked by the powder. Velocity rises as long as burning powder is still pushing the bullet. In Chattahoochee Munitions testing, that push is largely complete around 12 inches for 338 ARC. The 12.5-inch CM7S and the 10.5-inch CM15 sit at or near that point, which makes them the center of the lineup: close to full velocity with a compact suppressed overall length.
338 ARC Barrel Length and Supersonic Loads
Supersonic loads such as the 175 gr HP Match, rated at 2,075 fps from 16 inches, lose velocity as the barrel shortens. If supersonic hunting or longer shots matter as much as subsonic, the 16-inch CM7S and CM15 are the configurations to choose. The 16-inch CM15 keeps the 1:8 twist of the SAAMI 16-inch test barrel.
Choosing a 338 ARC Barrel Length
- 8 or 8.5 inch: The smallest suppressed host. Gives up some velocity for an overall length as low as 20.5 inches.
- 10.5 or 12.5 inch: Near full subsonic velocity with a compact overall length. The default choice for suppressed subsonic shooting.
- 16 inch: Rifle length with no NFA registration as a rifle, and more velocity for supersonic loads.
Suppressor Length Adds Up
A suppressor adds length to every configuration, so 338 ARC barrel length is only half the measurement. A short 338 ARC barrel with a suppressor can end up about the length of a 16-inch barrel without one, so the short barrels let a suppressed firearm stay handy in a blind, a vehicle or a stand. For subsonic ammunition an enclosed suppressor is recommended on both the CM7S and the CM15. See 338 ARC suppressor.
Barrel Length and the Law
In the United States, a rifle with a barrel under 16 inches is a short-barreled rifle under the National Firearms Act. The 8 and 12.5-inch CM7S and the 8.5 and 10.5-inch CM15 are offered as pistols or as SBRs, and an SBR configuration requires the NFA paperwork before transfer. The 16-inch firearms are rifles. Check federal, state and local law before you buy.
Twist Rate by Barrel Length
Twist rate is chosen for the bullet, not the 338 ARC barrel length, but Chattahoochee Munitions pairs them for the intended use: 1:6 on the 12.5 and 16-inch CM7S, 1:5 on the 8-inch CM7S and the 8.5 and 10.5-inch CM15, and 1:8 on the 16-inch CM15. See 338 ARC twist rate.
338 ARC Firearms by Barrel Length
- CM7S 338 ARC 8-inch bolt action pistol or SBR
- CM7S 338 ARC 12.5-inch bolt action pistol or SBR
- CM7S 338 ARC 16-inch bolt action rifle
- CM15 338 ARC 8.5-inch AR15 pistol or SBR
- CM15 338 ARC 10.5-inch AR15 pistol or SBR
- CM15 338 ARC 16-inch AR15 rifle
Uppers come in 8.5, 10.5 and 16 inches, and barreled actions in 8, 12.5 and 16 inches. See them all in Containment Zone 338, and read 338 ARC subsonic and 338 ARC ballistics.
338 ARC Barrel Length FAQ
What is the best 338 ARC barrel length?
For subsonic shooting, about 10.5 to 12.5 inches. In Chattahoochee Munitions testing, 338 ARC powder use is largely complete around 12 inches. Choose 16 inches if supersonic loads matter as much.
Is a 16-inch barrel worth it for 338 ARC?
For subsonic ammunition, it adds length without much velocity. For supersonic loads, the extra length adds velocity and keeps the firearm a rifle under federal law.
How short can a 338 ARC barrel be?
Chattahoochee Munitions offers 338 ARC down to 8 inches on the CM7S bolt action and 8.5 inches on the CM15 AR15.
Does a short barrel make 338 ARC louder?
A shorter barrel leaves more pressure at the muzzle, which raises muzzle blast. With subsonic ammunition and an enclosed suppressor, the difference is modest. Wear hearing protection.
What twist rate goes with each 338 ARC barrel length?
1:6 on the 12.5 and 16-inch CM7S, 1:5 on the 8-inch CM7S and the 8.5 and 10.5-inch CM15, and 1:8 on the 16-inch CM15.
Is a 12.5-inch 338 ARC an SBR?
With a stock, yes: any rifle with a barrel under 16 inches is an SBR under the NFA. The CM7S 12.5-inch is offered as a pistol or as an SBR.
Who makes a short-barrel 338 ARC rifle?
Chattahoochee Munitions manufactures 338 ARC CM7S bolt actions in 8 and 12.5 inches and CM15 AR15s in 8.5 and 10.5 inches, as pistols or SBRs, plus 16-inch rifles on both platforms.