When To Tune Your Radial Delayed Blowback Firearm

CMMG’s Radial Delayed Blowback™ operating system has solved a number of common concerns presented by straight blowback pistol caliber AR15s. With straight blowback ARs you have a heavy bolt carrier group and buffer and a stiff recoil spring keeping the action closed during firing. Besides the added weight compared to something like a direct-impingement 5.56x45mm AR15, the stiff spring and heavy bolt/buffer cycling back and forth ends up imparting a lot more felt recoil on a shooter. Once you start getting into pistol calibers with a wide range of loadings, tuning a straight blowback system to run reliably can be downright tough, and some calibers like .45 ACP or 10mm that are too much for straight blowback don’t have what it takes to cycle a traditional direct-impingement operating system. Thus, our Radial Delayed Blowback operating system was born, opening the AR platform to more pistol calibers than just 9mm with the bonus of cutting weight and felt recoil.

Unlike a direct impingement AR, Radial Delayed Blowback doesn’t use a gas system. Instead, backpressure from firing starts pushing the bolt rearward, forcing chamfered faces on the bolt lugs and barrel extension to engage each other and rotate the bolt before the BCG can continue cycling. This mechanical delay slows the BCG enough to safely cycle the action and allows the use of carbine AR15 buffers and buffer springs.


So why might I need to tune my Radial Delayed Blowback pistol or carbine?

While Radial Delayed Blowback might solve issues found in other pistol caliber ARs, especially 10mm, .45 ACP, and 40 S&W ARs, the specific ammo you shoot may or may not play well with the factory setup of your firearm. Additionally, if you like to shoot suppressed you may also need to tune your AR to better deal with the additional backpressure. The best solution for most is the use of our Action Tuning Kit.


When to use an Action Tuning Kit?

Think of an Action Tuning Kit (ATK) as an adjustable gas block for your Radial Delayed Blowback firearm. If you’re shooting hotter ammo or shooting suppressed, the increased backpressure could cycle the bolt too quickly, which could result in a spent casing not having enough time to eject out of the upper or strike the rear portion of the ejection port.

By adding one of the ATK weights to the BCG, delay is increased in the operating system which slows the bolt down and eliminates “overgassing”


What if I’m using weaker ammo?

For weaker ammo if you encounter short stroking, a condition where the BCG doesn’t travel rearward enough to completely cycle the firearm, you’ll want to avoid adding any ATK weights to your BCG. If you experience short stroking without any ATK weights in your BCG, you may need to use a lighter-weight buffer or consider using different ammo.


How do I install an Action Tuning Kit?

  1. First determine which Action Tuning Kit you need. For most the standard Action Tuning Kit will do the trick. If you have or plan on adding a Law Tactical or Sylvan Arms folding stock adapter, then you’ll need to use the shorter Action Tuning Kit, Law Compatible.
  2. Once you have the appropriate ATK, you’ll need to install one of the weights by sliding it into the back of the bolt carrier group, line up the holes in the BCG and weight, then hammer in the included roll pin until seated.
  3. The next step requires some trial and error. Whether you want to go from lightest to heaviest weight or vice versa, pick an ATK weight to start with and take a few shots to check function. If the installed weight doesn’t provide the desired results, drive the roll pin out with a punch and install the next weight, check function, and repeat with the next weight if necessary.
  4. Once you’ve figured out which weight works best for your setup and preferred ammo, the last thing you need to do is enjoy your newly tuned Radial Delayed Blowback AR by hitting the range and dropping some lead on those targets!


Have additional questions about tuning your Radial Delayed Blowback firearm? Reach out to our customer service team at customerservice@cmmg.com or visit cmmg.com/contact


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