CMMG Radial Delayed 9mm AR-15 Barrel and BCG Assembly 16"

Manufactured by CMMG
SKU: 99DE642
MPN: 99DE642
Manufactured by CMMG
2 Reviews
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Excited to build a pistol caliber carbine but don’t want to deal with spending time and money trying to find the correct buffer weight to reliably cycle the blowback action and then still have to deal with harsh recoil? Now you can forget about all that headache with the CMMG Radial Delayed Barrel and BCG assembly chambered for 9mm Luger. This kit utilizes the same radial delayed blowback system from the Guard series of PCC’s but allows you to build yours from the ground up, so you can build it to your preferences with ease. This system uses a bolt like an AR-15 without the gas system and with specific cuts on the lugs that force the bolt to rotate and delay the action from cycling in order to reduce felt recoil and increase reliability. This also has the benefit of being able to use a lighter BCG, so there is not a huge mass of steel slamming back and forth in your receiver. The gas key is still present for the sole purpose of interacting with the charging handle. Build your dream 9mm carbine with CMMG.

  • 16” barrel chambered in 9mm
  • Medium taper profile with 1:10 twist rate
  • Threaded 1/2x28
  • 4140 Chrome Moly steel with Nitride finish
  • Radial delayed blowback bolt
  • Requires enlarged ejection port for proper function
  • Lighter than standard blowback bolts

The 16” barrel in this kit is machined from 4140 Chrome Moly steel with a salt bath Nitride finish and threaded 1/2x28 for muzzle devices. This kit is also designed to function with the CMMG Guard 9mm receivers with enlarged ejection ports and may not work with other brands.

A leading manufacturer of AR-15 rifles, kits, and accessories, CMMG Inc. was established in 2002. Constantly pushing the edge, CMMG strives to develop and improve bringing you a product lineup that is second to none.
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Barrel CoatingSalt Bath Nitride
Barrel ContourMedium Taper
Barrel Length16
Barrel LiningSalt Bath Nitride
Barrel Material4140 Chrome Moly Steel
Caliber Gauge9mm Luger
Feed RampsMonolithic
Gas System LengthBlowback
Thread Pattern1/2 X 28
Twist Rate1:10
California Prop 65 warning

 WARNING: This product can expose you to chemicals, which are known to the State of California to cause Cancer and Reproductive Harm. For more information go to

Ratings & Reviews

2 reviews

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Smooth, reliable operation at a reasonable price


I've owned several straight-blowback PCCs and was less than impressed with all of them. I had pretty much given up on the concept, and the alternatives (MP5, MPX) were just way too expesive. I had seen the CMMG RDB setups, but didnt believe that it could possibly make that much difference. I was wrong.
<br>I decided out of a lack of other options to give this a try. I bought this 16" barrel and bolt kit, and built them into an Aero Precision XL upper. What I ended up with was a light, handy rifle that is incredibly smooth and soft shooting. I have about 500 rounds through it now, using one of the cmmg 9mm conversion pmags, and it has been 100% reliable. It's everything I was looking for that the straight blowback guns weren't, at less than half the price of an mpx or mp5.

This is Cool !!!


I purchased this for almost a year now and built my upper... No problem at all......Thanks