MK12 SPR Inspired Precision AR-15 Rifle




The Finished SPR Build.


Several months back, a close childhood friend of mine asked if some of the crew here on the channel would help in designing a custom build AR platform that would meet some of his specifications in its application.
Living on the wide, expansive plains of Montana, he spends a lot of his time farming, while enjoying the hunting of prairie dogs, coyote as well as other predators and varmint that region has to offer.  

If you watched our video on the Antelope hunt back in the fall, that’s his country.  The land out there eats up 500 yards quickly.  During the idea stages of the build, I shared with him information regarding the MK12 design and SPR platforms utilized by the military in order to gain maximum effectiveness out of the AR-15 platform at distance.  
MK12 MOD 
With the MK12 as the background influence on this build, he set out procuring parts.  We told him, buy once cry once, get the best and have a rifle you will not regret and can be confident in.  The parts list was as follows:

  • VLTOR Matching Upper and Lower Receivers with the VLTOR A5 Buffer system and VLTOR EMOD Stock.
  • Rainier Ultra Match 18” SPR Profile Stainless Shilen Blank 1:8 Ratchet rifling with a .223 Wylde Chamber.
  • VLTOR Flash Hider
  • Geissele SSA-E Trigger
  • BCM BCG
  • BCM Gunfighter Ambi Charging Handle
  • BCM 15” KMR Rail system.
  • BCM Gas Block
  • Burris AR PEPR Mount
  • Vortex EBR1 PST 2.5-10 MRAD Scope
  • *AEROSHELL 33MS GREASE FOR BARREL NUT THREADS.

We started the build in the morning, not particularly early, and were completed before lunch.  This was made easy in part by having quality and necessary tools readily available, and the knowledge of the members here on the channel.  

The Geissele trigger as expected, installed with ease, being that we have installed a few.  The Geissele action rod was a dream to use, allowing for proper torque specifications for the BCM KMR barrel nut (Aeroshell 33MS Grease applied) and mounting of the KMR Rail.  After final assembling, the rifle was function checked with dumby round-snap caps for feeding and ejecting by working the charging handle.    The scope was then mounted in a Burris AR P.E.P.R, leveled and bore sighted.  

That afternoon we ventured out to zero, break in and check reliability on the rifle.  

As expected, the rifle ran flawless with ideal ejection, lock back on empty magazines, reliable feeding, and accurate grouping for initial shots.  With the shooters plan to explore a range of ammunition and bullet weights ranging from 69-77 grain match loads, we expect this rifle to be sub-moa for years to come.  The Coyote and prairie dog population may have a little more pressure now with this rifle in the neighborhood.  




* Many of the steps we performed during the build process were not discussed. The BCM Gas block was pre-drilled by Rainier, and we removed it in order to install the barrel nut.  The gas block was then installed, pinned and set screws tightened with loctite.