Is my CMMG firearm Direct Impingement or Radial Delayed Blowback?

Rifle calibers are DI while lower pressure rounds like pistol calibers use the Radial Delayed Blowback system.

An easy rule of thumb to figure out what operating system your CMMG firearm or upper group uses is by considering the caliber it's chambered in. Rifle rounds and their higher pressures will be Direct Impingement whereas lower pressure pistol calibers utilize our Radial Delayed Blowback operating system.

The exception to this rule is .22 LR, which is low enough pressure that our dedicated upper and .22 LR conversion kits use a traditional blowback system.

Direct Impingement Calibers

  • 4.6x30MM
  • 5.56MM
  • 300 BLK
  • 350 Legend
  • 6MM ARC
  • 6.5 Grendel
  • 7.62x39MM
  • .308 Win
  • 6.5 Creedmoor

Radial Delayed Blowback Calibers

  • 9MM 
  • .40 S&W
  • .45 ACP
  • 10MM
  • 5.7x28MM

Traditional Blowback

.22 LR