The MK18 is a 10.3 inch short barreled AR-15 made by Daniel Defense. It’s grown in popularity in large part due to its utilization by Special Operators wielding it in the global war on terror. It will do most anything your typical AR-15 can do but better – with a couple of caveats.

When you have a barrel as short as the MK18’s you run into some issues. Mainly dwell time…

Dwell time is the time that your gas operated weapon maintains pressure to continue the cycling of the weapon. It primarily exists from the time the bullet passes the gas port in the barrel to the time the bullet exits the muzzle.” – (

The dwell time for the MK18 is horrifically short, to rectify this Daniel Defense opened up the gas port so that the gun is more forgiving of ammunition types like more weakly powered ammunition such as Tula .223. The problem is that if you are using full powdered 5.56 you’ll have an excess of gas being spit back into your face around the charging handle and the gas port. It isn’t bad but it’s certainly something that is different from your standard 14.5 or 16 inch AR-15. The upside is that this rifle will run with any ammo and reliability will never be a concern with your MK18.

If you want to fine tune your gas system you have several options available. You can install a gas block which allows you to change the amount of gas used to cycle your rifle, such as the excellent MicroMoa Govnah. Or you can go with a heavier buffer weight or stiffer spring. On my personal MK18 that I use I have opted for the VLTOR A5 recoil system which in a nutshell is a rifle length spring with a variety of buffer weights to suit your needs. The rifle length spring lowers the velocity on the bolt carrier group allowing for less perceived recoil. I also have a very heavy buffer for the A5 system weighing in at 6.83oz (A5H4) since I primarily run the rifle with a Surefire SOCOM RC suppressor, which significantly increases backpressure. Besides using the above mentioned you can also install charging handles which are meant to stop the flow of gas from reaching your face. One excellent product that I’ve heard of but I’ve yet to use is the PRI gasbuster. Regardless of the method you choose or combination thereof if you’re planning on running a suppressor on the MK18 consistently I would recommend having some type of gas mitigation system.

The upside to the short 10.3 inch barrel on the MK18 is how maneuverable and balanced it feels. Easy to manipulate in and around tight corners and indoors this is the perfect gun for short range work. While you do have loss in the speed of the 5.56 slug leaving the barrel, you also have more than enough to reach out and touch targets out to 300m with terminal efficiency as long as your ammo choice is sound. If you regularly push your AR past 300m and hope for excellent wounding ballistics the MK18 is not your gun. It isn’t a question of accuracy but rather bullet speed. It’s definitely an assaulter’s weapon and it excels in this role. Another great part of rocking a short barrel like the MK18 is even with a suppressor attached you still have a compact package. In my case I use a Surefire SOCOM RC which has a total length of 6.2 inches putting my total barrel length at 16.5 inches in length which is just over the length of many standard AR-15 makes and models you see out at the range today.