Tech Tip: How To Convert an AR-308 Rifle to 6.5 Creedmoor

Today's magic words: "distance" and "speed," two good things that rifle shooters typically want more of. That's what you gain when you convert a rifle chambered in .308 Winchester to 6.5 Creedmoor. Not everybody has to do that, says Brownells Gun Tech™ Caleb Savant, but if you're shooting long-range, you might want the 6.5 CM's higher performance. The good news is the 6.5 Creedmoor's parent case is the .308 Winchester, so conversion is very straightforward, as Caleb demonstrates for us by converting an AR-308.

 

PARTS: You'll need a new 6.5 Creedmoor barrel and possibly a new gas block. That's it. The bolt, receiver, and even the magazines, are the same for 6.5 Creedmoor. You can even use the same flash hider. If you're using a muzzle brake, you may want to switch to a dedicated brake designed for 6.5mm (.256") bullets, because you'll get better performance than sending the narrower bullet through the larger diameter .308 caliber exit hole.

 

TOOLS: Bench vise and upper receiver vise block. Caleb uses the AR-308 version of The Device vise block from The Device Manufacturing. You'll need a wrench to remove the barrel nut. Caleb has lucked out because he can use his Midwest Industries AR-308 armorer's wrench on the rifle he's working on. Other tools: adjustable torque wrench, whatever drivers you need to remove the handguard and gas block setscrews (Caleb's got the handy Fix It Sticks Field Armorer's Tool Kit), and some light grease, such as Brownells Action Lube Plus®.

 

TEAR IT DOWN: Check to make sure the rifle is unloaded. You'll probably want to remove any optics and accessories. Separate the upper receiver from the lower and remove the bolt-carrier group and charging handle. Using the vise block, clamp the upper receiver into the bench vise. Remove the muzzle device, handguard, and gas block / gas tube. Next, the barrel nut. And that .308 barrel should slide right out.

 

BUILD IT BACK BETTER: Apply a small amount of Action Lube Plus® to the new barrel's barrel extension, including its front shoulder. Insert the barrel into the receiver, then reinstall the barrel nut, snugging it up hand tight. Use the adjustable torque wrench to tighten the barrel nut the rest of the way. Caleb sets his to 45 ft.-lbs., which should be plenty for most barrel nuts.

 

Reinstall the gas block and gas tube. If the new barrel's outside diameter is different from the old one, you'll need a new gas block. If the ODs are the same, you've lucked out! You can re-use the old gas block. Make sure the gas block is aligned vertically. Snug down one of the gas block setscrews, then back off slightly. Use the driver to fine-tune the gas block position. When it's perfectly vertical, tighten down the setscrews. Caleb tightens his to 25 in.-lbs. (note that's INCH, not foot pounds).

 

Install the handguard and muzzle device. If you're installing the muzzle device using shims, check out our video, "Quick Tip: How To Time a Muzzle Device With Shims." Reinsert the charging handle and the bolt-carrier group.

 

Now, grab your .308 Winchester GO and NO-GO headspace gauges. Clean the chamber. Insert the GO gauge in the chamber, with the relief cut facing the extractor. Push the bolt closed. If it closes, it's good! Now, do the same with the NO-GO gauge. The bolt should NOT close. If it doesn't, your new AR-308 rifle chambered in 6.5 Creedmoor is good to go.... once you reinstall the upper receiver on the lower.