The AR-15's been chambering .22-caliber rounds (and its variants, .30-caliber) for decades. But recently, new calibers have been made available for the AR's .308 platform: The 6.5 Creedmoor round. What's the benefit? Is it worth going with 6.5mm over .308 Winchester? Let's get the big questions answered first.
6.5mm AR FAQ
Q: What is 6.5 Creedmoor?
A: The 6.5mm Creedmoor round is a long-range centerfire rifle cartridge based on two other rounds: The .30 Thompson Center, and the Italian military's (very old) 6.5x52mm Carcano cartridge, whose bullet measures .268" in diameter. The .30 TC uses a 0.264"-diameter bullet and was made by Hornady in 2007. Its goal was to deliver .30-06 Springfield performance in a round as small as the .308 Winchester. To deliver that kind of performance, 6.5 Creedmoor superseded the .30 TC.
Q: How does the Creedmoor perform?
A: This round was purpose-built for bench shooting and professional matches. It's easily capable of ringing steel at around 1,000 meters. Improved rifles with accurized barrels can achieve performance at 1,200 meters. Most out-of-the-box ARs chambered in Creedmoor can easily hit 12" targets at 800 meters, with appropriate optics.
Q: Which AR platform does the 6.5 Creedmoor fit in?
A: The 6.5 Creedmoor round fits in the LR-308 platform, which is the modern equivalent of the ArmaLite AR-10. The AR-10 is a larger variant of the AR-15, chambered in .308 Winchester. The LR-308 was developed by DPMS Panther Arms. It won favor with shooters who remarked the LR-308 performs just as well as the AR-10 for a lesser price.
Q: What's 6.5 Grendel? Is it like Creedmoor?
A: Yes and no. The 6.5 Grendel cartridge is made to provide better performance in the AR-15's 5.56/.223 platform, just like how Creedmoor's meant to improve performance in the .308 platform. Grendel is shorter and about 18% slower than Creedmoor, but they fire the same .264" bullets. This guide compares both 6.5mm cartridges.
Q: Can I install a Creedmoor upper on my existing .308 AR?
A: Yes. The Creedmoor round shares many parts with the LR-308. Let's get into that topic now.
Building a 6.5 Creedmoor AR
Building a 6.5 Creedmoor "AR-10" is about the the same as assembling any LR-308. This round was made for long-range shooting, so your rifle will be, well, a rifle. There are few to no Creedmoor pistol builds. This round simply isn't built for short barrels. Before we dive into picking out the optimal parts for a 6.5mm build, let's look at performance and specs.
- Case Length: 1.920"
- Overall Length: 2.825"
- Bullet Diameter: 0.264"
- Case Capacity: 52.5 gr H2O
- Max Pressure (CIP): 63,091 PSI
- Max Pressure (SAAMI): 62,000 PSI
Data collected using 28" barrel.
- Muzzle Velocity: 3,020 ft/s
- Muzzle Energy: 2,430 ft-lbf
- Muzzle Velocity: 2,710 ft/s
- Muzzle Energy: 2,283 ft-lbf
Quickly summarizing, the Creedmoor cartridge boasts some impressive numbers: Velocity is comparable to that of the powerful .300 Winchester Magnum (2,930 ft/s) with a bullet weighing about half as much. This lightweight bullet coupled with high velocity allows the Creedmoor round to maintain supersonic speeds past 1,000 meters. Because of this, it boasts a high ballistic coefficient. But enjoying all that velocity and high BC means building the perfect rifle. So, let's take a look at the optimal setup for building a 6.5 Creedmoor AR.
This 6.5mm cartridge uses about 50% more powder than the 6.5 Grendel, and it's even faster than .308 Winchester once it's up to speed. Burning all that powder means building a big, long gun. But you don't need to make your rifle weigh 20 pounds. Let's figure out the optimal barrel length and configuration for this setup.
Lucky for us, one enthusiast at Rifle Shooter tested the effects of barrel length has on Creedmoor's velocity. Shooter Bill Marr cut down a 26" Creedmoor barrel to a whopping 17", barely longer than the average 5.56/.223 barrel, which is 16". Using a ballistic chronograph, he was able to calculate the following muzzle velocities for Hornady's 147-grain ELD Match loads. This load's optimal muzzle velocity is advertised to be 2,695 ft/s. Here's Marr's data:
Length vs. Muzzle Velocity (147gr ELD Match):
- 26" - 2,728 ft/s
- 25" - 2,691 ft/s
- 24" - 2,677 ft/s
- 23" - 2,637 ft/s
- 22" - 2,638 ft/s
- 21" - 2,609 ft/s
- 20" - 2,577 ft/s
- 19" - 2,542 ft/s
- 18" - 2,502 ft/s
- 17" - 2,492 ft/s
The data show that optimal velocity for the ELD Match load is achieved at 25", which is quite long. But unlike other rounds, this cartridge doesn't lose much energy in shorter barrels. Cutting the barrel down from 26" to 17" reduces total velocity by only 8.7%, or 236 ft/s. This is a mild loss. More importantly, Marr tested the Creedmoor's other popular loads and found velocities tend to stabilize around 22" to 20". Loss of total velocity per inch remains below 100 ft/s until going shorter than 21".
So, to achieve the most velocity (and thus, accuracy) with the shortest possible barrel, a 6.5 Creedmoor AR or other 6.5mm rifle should use a 20" to 22" barrel. Shooters firing within 800 yards will not suffer noticeable losses in performance if using a barrel that's even shorter. Others report capability of hitting a 12" target consistently at 1,000 yards with this barrel length range.
Twist rate is straightforward for the Creedmoor round: Stick with a 1:8 twist. This rate's perfect for stabilizing the Creedmoor's heaviest (143gr) loads, which are best for both long-range shooting and hunting. This rate also won't over-stabilize lighter (143gr to 120gr) 6.5mm loads, allowing you to accurately shoot all Creed cartridges.
With a 22" to 25" barrel and 1:8 twist rate, the 6.5 Creedmoor is capable of pushing a 147-grain ELD Match round to 1,200 yards. With this configuration, match loads will remain supersonic to nearly 1,400 yards and they'll be capable of taking most American game at 600 to 650 yards -- if you're brave enough to take antlers that far away.
Gas & Buffer
Things are kept simple here. You'll want a rifle-length gas system and Heavy or "H" buffer weighing 3.7 ounces to reliably cycle Creedmoor loads without short strokes or, inversely, excessive recoil. A mid-length gas system and the same "H" buffer can be used on rifles with a barrel measuring 17" to 18". A "+2" or extended rifle gas system can be used on Creedmoor barrels measuring 24" or more.
6.5mm Parts Compatibility
You'll be happy to know building a Creedmoor rifle is easy, because it's almost identical to the average LR-308 rifle.
Creedmoor shares these parts with .308 ARs:
- Stripped upper
- Stripped lower
- Lower parts kit
- Bolt carrier group
- Charge handle
- Buffer tube
- Recoil spring
- Barrel nut
Only these parts are unique to Creedmoor:
- Barrel extension
Technically, you don't need to build a new rifle if you already own an LR-308. You can opt to simply swap barrels, though this may require a gunsmith and/or specialty tools if your barrel nut is seized. A new barrel nut should be used if you decide to swap barrels. You should confirm the barrel's diameter at the gas port if swapping, too. If spec'd correctly, your .308's gas system, buffer, magazines, internals, and bolt can all be reused.
Completing Your Build
If you choose to build an all-new shooter instead of converting a .308 gun, you can piece your 6.5mm AR together or simply grab a Creedmoor build kit. Build kits remove most of the guesswork of configuring your rifle by providing the optimal barrel, twist rate, and gas system.
Using The LR-308 Receiver
Since Creedmoor uses .308 AR magazines and internals, it uses the same firearm component of the LR-308, which is the stripped lower receiver. This is the only part of the rifle considered a firearm under federal law. You can get your hands on a stripped lower by purchasing one from a dealer. Or, you can make your 6.5 rifle entirely custom by fabricating a billet .308 80% lower.
No matter your choice, your receiver should be assembled with an AR-10/.308 parts kit. The Creedmoor upper installs on the .308 lower using regular takedown pins. No modification is required.
Here are the important takeaways to remember if you're building a 6.5 Creedmoor AR:
- 6.5 Creedmoor is a .264" round in a .30-cal casing that can reach beyond 1,000 yards.
- Velocities range between 2,700 and 2,900 FPS, depending on barrel length and loads.
- The Creedmoor round is built on the LR-308, DPMS Panther Arms' version of the AR-10.
- It uses an AR-10/LR-308 bolt, LR-308 parts, and a rifle gas system with .308 or H buffer.
- Optimal barrel length is between 20" and 22". A 25" barrel provides max velocity.
- Optimal twist rate is 1:8. This rate can handle all light and heavy Creedmoor loads.
DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At 80-lower.com, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.