Going Short with the MDRX Micron Conversion Kit

One of the endless discussions amongst those with real world experience clearing buildings with rifles is barrel length.  Most experienced trainers agree a 16” rifle or 18.5” shotgun will work, not ideal, but capable with training. Laws, policies and restrictions can make short barrels difficult to acquire so longer barrels remain the norm. Regardless of the obstacles to getting them,  clearing buildings or working in tight spaces with a shorter barrel is easier, faster and more efficient. Those who can go short generally will and millions of people buying AR pistols leaves little doubt. Are there compromises, sure, but as a practical matter so long as it runs, maintains accuracy and does the job the shorter the barrel the better.

Considerations for Short Barrels?

         There are three considerations when going short with your rifle, function, application and effectiveness. Function is critical, we are talking about a lifesaving tool, not a toy. If it won’t run with the issued or available ammunition it’s useless. Not every operating system or caliber works with short barrels, pick one that works with the ammunition you will use.  

         What it’s used for is almost as critical, caliber and system must be applicable to your environment.  Big bores are fine, but in most cases unnecessary, seldom practical and often detrimental.  Unless your job or task requires a big bore don’t waste your time, money, and hearing.  Most “experts” list 300 yards as practical, that’s at least 200 yards farther than real world experience. The vast majority of self-defense or LE encounters are across the room, maybe across the street and the 5.56mm does that job just fine with lower cost, less recoil, and more choices. 

         In the end it must be effective making ammunition choice important. Short barrels used to be problematic,  not anymore.  Several companies have loads designed specifically for short barreled rifles. Hornady’s 55 grain Critical Defense performed very well in my simulation tests from 7” barrels, and superbly in a 11.5 inch. Same with Barnes 50 or 55 grain TSX, or Black Hills Ammunition’s load using the same bullets.  Given the proliferation of 5.56mm  “pistols” and more SWAT teams using short barrels there are several proven choices. Just make sure it works in your rifle, SBR, or pistol. 

So, what’s the ideal barrel length?

         Having tested short barreled rifles on a police department and SWAT team for decades the best overall length for a 5.56mm is 10.5 to 11.5 inches. Most rifles, including the AR will run most ammunition reliably, accurately and effectively out to at least 300 yards. For patrol officers it’s about perfect, especially unsuppressed.  Compact, effective, and easy to maneuver in an urban environment they are excellent.   Given the right suppressor both piston and direct impingement rifles will work, they just turn into a 16” rifle.  For dedicated entry or suppressor use the 8 inch (or similar)  using a piston system has proven the most reliable. They remain effective and can be operated with a suppressor so long as you have a way to turn the gas down.  One notable exception is the Bull Pup, running a 11.5 inch barrel nets the same length as a 7” standard rifle.  Not for everyone, but if you can work through the ergonomics you get all the advantages of a 7” without any of the issues. They remain my preference and Desert Tech’s introduction of the 11.5 inch Micron 223Wylde SBR conversion kit for their MDRX I have approached short barreled Nirvana. 

Desert Tech’s 11.5 inch SBR Micron Conversion for the MDRX

         I have been running the MDR since before it was available, it remains one of my favorite rifles, especially in 5.56mm. Testing and running the 16.5 inch barrel from prototype to production it has been my primary carbine ever since. Runs great in 308, just not useful for me, especially since the 6.5 Creedmoor has become available. My MDR has seen thousands of rounds of 5.56mm without a hitch and does anything I will ever need. Unsuppressed it is compact, accurate, and provides optimal effectiveness for the  5.56mm. Suppressed it remains shorter than your typical AR, but it does negate its biggest advantage, compactness. Still, I prefer a 11.5 inch barrel and their new SBR kit provides just that.

         This is an SBR conversion, you will need to complete the proper paperwork, there is no MDR Pistol. You could also order an SBR up front, you end up with the same modularity either way, just a matter of process, just understand the requirements up front. If you have a side eject model this is a barrel and hand-guard swap, five minutes tops. With forward eject models the side ejection panels and bolt are required.  Hand-guard is short with a couple of M-Lok slots. There was room for a QD sling attachment and a light, but that’s about it.  The design is functional allowing for a solid hold even with my large hands. Using the supplied flash hider / compensator it is scary short so you may opt for a single point but it worked for me with a Blue Force Vickers sling. The Muzzle  device was surprisingly pleasant to shoot with very little blast in my face.  Threaded ½ x 28 you can swap it out for the diverter of choice, but this works very well just be careful with hand placement. 

         Using the X2 DevGroup Orion X suppressor this was pure joy to shoot.  No back pressure, no change in operation and less gas in your face. It’s less than a foot from your face making it louder than most carbines, but it remains a 11.5 inch barrel so quieter than a 7” AR.  Adjusting the gas it’s workable with most suppressors and the piston system keeps it reliable and cleaner. The ejection port is right at your ear (and nose) though, so it’s all a tradeoff. Adding the Armageddon Gear suppressor cover kept it workable under rapid fire, things get hot pretty quickly so run this without a can cover at your own risk. 

         Accuracy was no different than the 16.5 inch barrel at 50,100, and 200 yards. Leupold Optics DEVO was already zeroed at 200 yards with the 16” barrel and my first round rang 12” steel a tad low and left.  The LCO was zeroed at 50 yards and it stacked Hornady’s 55 grain Critical Defense, at 100 yards it was well under an inch. While I missed my forward eject it ran flawlessly throwing brass consistently at about 2:00 and did not pepper my face running it left handed. 

         Running in and around the truck was impressive, especially unsuppressed, in fact you had to work to make sure that brake was outside the window, another place I missed my forward eject. Adding the suppressor it was just about perfect in and out of the truck and working the shoot house.  Short, but not too short, and quiet enough to use without taking you or those around you out of the fight. Even suppressed it felt lighter, although the side eject helps, but balance was excellent providing solid control, running the brake alone it reminded me of running an FNP90. 

Bottom Line

         This worked well enough it will cause a conundrum for me.  My MDR is currently set up with the 6.5 Creedmoor, a setup I really like since it gets used for some longer range applications. Once a permanent kit arrives it will be difficult to choose between the two configurations, a good problem to have for sure.  It is a simple conversion that is compact, reliable, and the 11.5 inch barrel loses very little ballistic efficiency.  It is incredibly handy in and out of a truck, a place I find myself often and perfectly suited to entry duty.  If you are looking to go short and not married to an AR this needs to be on your list as it really does not get much better.

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