The Mitchell Defense DOC AR-15 Line: Good Medicine

The Mitchell Defense DOC AR-15 Line: Good Medicine
The Mitchell Defense Shorty DOC SBR 5.56 MLOK.

A quick look at Mitchell Defense, its DOC line of AR-15s and what sets them apart from the rest.

AR-15 manufacturers often claim to have a secret sauce, something they do differently that sets their weapons apart and above the rest. Admittedly, when I hear this, I’m typically skeptical.

When I stopped by the Mitchell Defense lane at CANCON Georgia, the owner, Nathan Mitchell, gave me a similar pitch about his company’s guns. My skepticism was cut short after sending just a few rounds downrange.

As promised, the Shorty DOC SBR 5.56 carbine was noticeably smoother and flatter shooting than the average AR-15. How did Mitchell Defense accomplish this? It wasn’t done with an obnoxious muzzle brake or through the addition of extra weight, but instead through the company’s buffer system and manufacturing process.

The company's owner/founder Nathan Mitchell putting rounds downrange at CANCON Georgia 2023 with a Shorty DOC SBR in 5.56.

The Buffer System

Much of Mitchell Defense’s magic comes from its proprietary buffer system. It uses a specially treated flat wire spring that provides approximately 30-percent more forward pressure than normal springs and lasts much longer. The company claims traditional springs begin losing their strength at around 6,000 cycles, but Mitchell Defense flat springs don’t start doing the same until after 200,000 cycles.

Mitchell Defense's flat wire buffer spring (bottom) vs. a traditional one.

Nathan Mitchell has stated his company’s designs “stand firmly on the pillars of Accuracy, Durability, and Reliability”, and the flat spring’s qualities contribute to those last two points. It also enhances the guns’ accuracy, in the sense that it reduces recoil and allows for faster follow-up shots thanks to the minimal muzzle movement. When shooting AR-15s with traditional buffer systems, you may notice that distinctive metallic “twang” sound after the buffer cycles back into the tube. The Mitchell Defense buffer system eliminates this as well, resulting in a quieter shooting experience.

Another look at the flat wire spring with the buffer installed.

While the DOC carbine I shot was also equipped with a suppressor (this was at CANCON after all), the recoil reduction was far too significant to be entirely attributed to the can. When I put the reticle over a steel plate at about 25 yards and pulled the trigger, the red dot’s movement was barely perceptible. Requiring only minimal effort to hold the rifle steady, I was able to keep pulling the trigger and ring steel with every subsequent shot. Of all the production AR-15s I’ve had the pleasure to shoot, the Mitchell Defense is most deserving of the descriptor “flat-shooting.”

Thermal-Fitted Barrels

As mentioned, accuracy is one of Mitchell Defense’s priorities when designing guns. While ARs have never been known for extreme accuracy compared to bolt-action rifles, Mitchell decided to challenge that notion. This is mostly thanks to the company’s use of thermal fitting to install its barrels.

One of Mitchell Defense's thermal-fitted upper assemblies.

Thermal fitting is a process in which the part of the upper receiver that accepts the barrel is made to be slightly smaller than the barrel extension itself. This means that at room temperature the barrel cannot be inserted. To install the barrel, the upper is first heated until it has expanded enough to accommodate it. The barrel is then inserted before the receiver cools down and returns to its original size. The result is an incredibly tight connection between the two components. Combine this with Mitchell Defense’s billet uppers that feature a “near-perfectly flat surface for the barrel seat”, and you end up with one very accurate setup.

BCG And Coatings

The bolt carrier group is a crucial component of any build, and it’s another area where Mitchell Defense has made several improvements. Called the MD Enhanced BCG, it features some relatively “standard” BCG upgrades such as optimized carrier key screws and a staked and sealed gas key, but there’s more to it than that.

Mitchell Defense grinds the skids on each BCG perfectly flat, even and sized exactly to its individual upper. Combined with the BCG’s ArmorLube coating (the latest mil-spec M4 BCG coating), you get a very smooth action with a minimal amount of friction. The friction is further reduced using E Series Cerakote throughout the guns. Keep in mind that less friction not only increases the parts’ durability and longevity, but it produces less heat while cycling too.


It’s little details like these that result in guns that feel superb to shoot. The enhancements to the BCG didn’t just impact the smoothness of the action but also did an excellent job of minimizing the amount of gas going back into the shooter’s face. The Shorty DOC was suppressed, yet I could breathe better while shooting it than I have when behind some particularly poorly built, unsuppressed ARs.

Parting Shot

If you're still not convinced that Mitchell Defense ARs are a cut above the rest, that’s fine. While the company is happy to sell its firearms on the commercial market, it’s law enforcement groups and government agencies that comprise the bulk of its sales. The Pennsylvania State Police is currently Mitchell’s biggest buyer, but plenty of other groups like SWAT teams are making the switch to Mitchell Defense guns too. Considering the higher-than-average price of the company’s products, these groups must also believe that the increased performance is worth the increased cost.

Mitchell Defense has stated that it builds its guns as if they were to be “the last rifle you will ever have.” That comes with a price tag that won’t be within everyone’s reach, but for those who get one, the odds are that it will last longer than you do. The company is confident enough in this statement to back its guns and components with a lifetime guarantee.

The Mitchell Defense Slick Rat Dog SBR PCC in 9mm.

For those interested in buying one, you should also know that there are more models offered aside from the Shorty DOC 5.56 carbine. The DOC line also includes 16-inch 5.56 rifles, a 6mm ARC rifle and some short-barreled .300 BLK models. The company also has the Rat Dog PCC line in 9mm and the Pipe Hitter line with models chambered for .308 Win., 6.5 Creedmoor and 8.6 BLK.

Whichever you pick, just know that it comes pre-treated with Mitchell Defense’s medicine.

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