9mm Radial Delayed Blowback and Choosing The Right Lower Configuration For You

After months of scouring the internet for articles and reviews of CMMG®’s patented Radial Delayed Blowback, you’ve finally decided to go ahead with the purchase. And you’ve decided you want a 9mm! Then, you see that the 9mm is offered in four different platforms … so, now you’re asking yourself, “which one do I want to purchase?”, right? Now you probably have more questions, and finding answers that are not highly opinion based is becoming increasingly difficult. 
Ultimately, it’s all going to boil down to whichever one best suits YOUR needs, as a consumer. While functional reliability of the upper group is going to be pretty much on par across the board, we’re going to go over the basic pros and cons, from a practical perspective, of each individual platform that we offer for the 9mm Radial Delayed Blowback. This should help you make a more well-informed decision on which option would be best for you.
The Mk9™
The Mk9 has the distinction of not only being the first and original 9mm that CMMG offered as a traditional blowback style firearm, but also the latest offering in the Radial Delayed Blowback 9mm family.
The Mk9 utilizes steel body Colt SGM-pattern magazines. The great thing about this is that the magazines are very durable and can hold up to quite a bit of abuse.
Since the Mk9 is a dedicated 9mm lower receiver, you will be limited to just the one caliber with this option.
The MkGs™
The MkGs lower was the original configuration for the 9mm Radial Delayed Blowback. This design was based on the popular demand for a lower that utilized Glock pistol magazines.
This is the recommended configuration for those that own or are looking to purchase a Glock firearm that utilizes a double stack magazine (the Glock models 17, 19, and 26, for example) and want that ability to interchange one magazine between two platforms. This is a popular option for competition shooters. It should be noted, however, that the MkGs magazine well is designed based on Gen3 and newer magazines. The best part about this is that Glock magazines are plentiful. And, if you don’t want to be limited to just 9mm, you can purchase the .40 S&W RDB upper group and use it on the same lower group!
The Mk17™
The Mk17 was designed from an overwhelming request for a lower that would utilize another very popular handgun amongst customers - the Sig Sauer P320.  
The P320 magazine is another steel body magazine that can hold up well to abuse, and if you already own a P320 or are looking at purchasing one it means you’ll have another option for utilizing those magazines!
You will be limited to the one caliber with this lower. Additionally, P320 magazines are not as cost-effective as some of the other options, although they do offer good, solid construction. While there are some manufacturers that make aftermarket magazines, they have proven less than reliable, so we highly recommend staying with Sig Sauer metal magazines.
The Mk4™
Last, and certainly not least, is the Mk4 lower. Working with MEAN Arms, CMMG was able to utilize a version of the ENDOMag insert that was designed specifically for the Radial Delayed Blowback system. The inserts work with Gen2 and Gen3 Magpul PMAGs, and the complete CMMG conversion magazines are available in either 10 or 30-round capacities.
The Mk4 is easily the most versatile of the options. This is a standard AR15 lower group, so any caliber that would work on a standard AR15 lower can also be used on this one. A two-pack of inserts is available for purchase for those that live in non-restricted states, and Pmags are available just about anywhere and are wallet friendly. Or, if you have a few PMags just lying around, these inserts can certainly help knock the dust off and breathe new life into them! This is also a good option for those that want the Radial Delayed Blowback system, but do not own or intend to purchase a Glock or a Sig P320 and want to experiment with other AR calibers without having to purchase a completely new firearm, or, you can purchase just the 9mm upper group and conversion magazines to use on an existing AR15 pistol or NFA lower that you may already have.
That sums up the differences of each available option for our 9mm Radial Delayed Blowback. We hope this was helpful and informative. If you have any other questions before you decide to “pull the trigger” on a purchase, our Customer Service Team is more than happy to answer them and can be reached via email at customerservice@cmmg.com.
We look forward to hearing from you and hope you have a safe and fun time with whichever CMMG product you choose to purchase! And remember, every product is backed by CMMG’s Lifetime Product Quality Guarantee!
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