Why You Already Own a Special Purpose Rifle

Why You Already Own a Special Purpose Rifle

The SPR is a wonderful piece of kit… and you already have one sitting in the gun safe. In a military setting, the SPR/DMR style builds are used by the squad designated marksman. Typically this role is filled by a soldier who has had some additional trigger time after a DMR class. A designated marksman isn’t a MOS or ASI, but rather an additional training course. The rifle itself is an accurized platform from which the squads assigned designated marksman can use this training to increase the effective range over the issued M4 carbines.

My interest in the SPR is that it really takes advantage of the Stoner design: It allows the AR15 to express its best qualities by complimenting the designs accuracy capability, its adaptability, and its ergonomics to package a match accurate fighting rifle. I can’t think of another build which allows the rifle to hit targets out to its maximum terminal effect with near sniper rifle accuracy, but at the same time remains small enough to utilize indoors in its semi-automatic role. That’s an awesome rifle that we have sitting in our gun-safe. A basic AR15’s capabilities are not limited by its design, but rather by the ballistic qualities of the bullet you stuff in the chamber and the knowledge of the shooter.


Components used to clone the Crane SPR are getting harder and harder to find, so take inspiration from it, but utilize the better components available to civilians to create your own DMR style build. Or a GPR.

One area where the military is lagging behind, as nice as clones are… is weight. Every AR15 manufacturer these days produces a rifle which can be pressed into a DMR style role. There is no formula, only additional training and some glass. Your bone stock MP15 can easily be shot out to 600 yards with a FF barrel and match ammo. Military style clones lack the market adaptability of current AR15 design. They are stuck with heavy rails, issued optics, and the year before last years components. While the military has “Special Purpose Rifles”, we as civilians have General Purpose Rifles.

The Civy G.P.R. vs. the Mk12 Mod 0 / Mod 1

Think of the SPR… you likely saw in your mind the Mk 12 Mod 0 or Mod 1. These rifles as civilian clones are popular, and very distinctive builds, but they are unnecessary. Lighter modular rails, better optics choices, and better everything are available to us in the civilian market. Take any free floated, off the rack rifle, and your likely to have a rifle very much suitable for a DMR role with addition of only glass and match ammo. A “general use” AR15 can take advantage of the platforms versatility with a variable optic and keep the precision of a military SPR build while being lighter, and more affordable to the civilian. Below is a chart from a military power-point which shows the difference glass and ammo makes on a M4A1:

M4A1 accuracy vs M16A2

With glass and match ammo, the M4A1 can be utilized in a DMR role. The iron sighted M16A2 can still hit that 600 yard target, but clearly glass offers the shooter some huge benefits.

The M4A1 doesn’t have a match barrel, but you can see how tight things get once you give the shooter an ACOG and 77 grain ammo. So if practically any AR15 can function as a DMR style rifle, then what do we need to take advantage of the capability?

Glass and Marksmanship:

Let’s assume the basic Ar15 rifle is free-floated as many civy AR’s these days come from the factory with a rail equipped. So whats the first upgrade we need on the rifle? The AR15s effective range is far further than the quality of human vision at the edge of that range. Glass is of primary importance as the human eye lacks the resolution to make out targets downrange effectively. Can you imagine having to shoot back at someone who was prone, camouflaged, and 4-5-600 yards away? I took some experiences a relative shared with me once and incorporated them into my shooting philosophy. He himself was a designated marksman in Afghanistan. His thoughts are summarized as follows: you can’t see shit, the enemy hides and is a fleeting target. The enemy gives you no time or little time to implement your marksmanship training.

With that thought, I realized that glass is of the utmost importance on a fighting / SHTFantasy rifle. Going with the 4x ACOG initially was a good choice for a lightweight build, but I wasn’t using the ammo tailored for its BDC. Being non-adjustable I had to tailor the ammo to fit the optic by tuning my reloads. I didn’t like selling it, but I had to move onward and try something new. I found the flexibility of the Vortex Razor HD 1-6x refreshing save for its weight.  So with my glass better tailored to the heavier match ammo I shoot, along with the extra magnification… I can see everything down range that I could want to shoot at. Now what is the best way to shoot at it?


A fixed environmental support and a variable optic being utilized by a Marine with his SAM-R.

Marksmanship training needs to focus on expedient methods of hitting a target. Quick, easy, even though “less accurate” methods would be more desirable to slow, precise, and more accurate methods if our target is moving in reaction to our presence. Quickly getting on the trigger, using the BDC to quickly throw rounds downrange would at least give you the chance of a hit vs not having enough time to set up a precise shot should the target retreat into cover. Furthermore, there was a study done, and ill be damned if I can find it, that suppression is a function of how loud the supersonic snap is perceived by the target… which is a function of how close the round was to the intended target. Even if you missed, rounds striking close to the target would likely have a suppressive effect. Dust and dirt would be kicked up if rounds strike low and if you are a few inches high on the target then the supersonic snap would hopefully force a retreat into cover which would be important if the target was on the trigger first.

Ergo: Setting up a fighting rifle / DMR / GPR should be built around the philosophy of “If I can’t shoot at it quickly before the target retreats, then my hit probability will be zero.” So shoot at it quickly, and accurately enough to cause suppression if we miss? Yes. What will help us with that?

What we want:

  • A fixed BDC reticle matched closely to your “match accurate” loading
  • Enough magnification to I.D. and fire upon a target at your theoretical maximum effective range
  • Ammo with a high ballistic coefficient to help reduce wind push and keep your rounds as close to the BDC stadia as possible at each given range
  • Implementing fast and expedient methods of rifle stability such as a bi-pod or environmental supports
  • Longer barrels increase velocity which reduces windage error: use the longest barrel which is feasible into your build

We don’t want:

  • Slinging up with a traditional turner sling or web sling: Takes too long and faster shooting slings exist
  • Low BDC ammo or ammo with mediocre accuracy: Setting up a DMR around say 55 grain ammo would increase wind error and push you away from the BDC
  • Calculations: No time to use a mil-dot unless you have calculated ranges beforehand and have practiced using the mil-dot reticle as a BDC
  • Adjusting your dope: possibly no time if you are getting shot at, use the BDC and practice wind calls without making adjustments
  • Shorter barrels will theoretically cause more deviation by increasing time to target and having more wind drift

So for a quick summation: I want to start shooting at my target rapidly by using my BDC and expedient marksmanship methods, and I want rounds to strike closely, if not hitting the target, in the small allotment of time I have to hit said target. Should I miss, I want my miss to be small. My target should see dust, dirt, or secondary projectiles striking closely, or if I miss high, the supersonic crack should be close (loud) enough to suppress the target. The best way to do this is with a gun/projectile combo which allows me to quickly use a BDC to range and fire upon my target and by using match ammo that deviates off the BDC stadia as little as possible in relation to random environmental conditions.

Wrapping Up:

There is a DMR inside of Every AR15 just waiting to get out. A nation of marksman can exist if we emphasize the value of practical marksmanship. I value High-Power, but I realize what it teaches you is good for the basics of pure marksmanship and the fundamentals associated with that, but it isn’t as much value as more practical methods of marksmanship. The romanticism of the American Rifleman stems from his actions during war. The American Rifleman is a practitioner of a highly valued martial art. Martial arts evolve with the time, and incorporate new ideas and methods to keep the practitioner effective. A civilian AR15 topped with variable / magnified optics and match ammo becomes a G.P.R. which is capable of everything from target shooting, to 3 gun, to combat. I think it’s a great tool for the modern American rifleman and we should all have a GPR equipped in the safe.


Written by lothaen


  1. E.D.M. · May 6, 2015

    I concur whole heartedly with everything you said. My caveat, of course, is that focused practice with precision shooting helps you be more accurate in those moments where getting the shot off is more important. If the shooter’s fundamentals are sound and well practiced, then a 50% drop in accuracy due to speed still ends up being more accurate than someone who does not practice the fundamentals.

    If suppressive fire is the the key, then a slightly mismatched BDC is still usable if the intent is volley fire. If a target is 400 yards away, I put the 400 stadia line on the location and fire five shots in rapid succession. Probability says that one of those shots should land where I want it to, and all five should at least offer suppression. I believe that was the intent of the S4G system I wrote about a while ago.

    On that note, how is your 18″ Criterion working out for you? I keep eyeballing one for myself, as well as the Rainier Mountain series 18″ Mid Weight

    • lothaen · May 6, 2015

      I had the criterion at the range a few days ago, and I am still impressed with it. Wind was 5-10 mph with intermittent gusts on a 81 degree day. I used On-Target software to analyze a 200 yard group:

      A tight 5 shot cluster on the target was a half minute, adding the next two outliers presented a 6 shot cluster which was .8 minutes, and adding the 7th shot which was pushed right but not so far as for me to reasonably exclude it opened things up to 1.3 minutes.

      Loading was 25 grains of Varget with Sierra 69 grain match kings.

      The other 3 shots were too far off center for me to count them and were consistently pushed right which aligns with the wind direction. I am comfortable with the 7 shot data point at this time, and I will use this loading and zero for High-Power which was my intended use.

  2. Colorado Pete · May 7, 2015

    Good article.
    I second E.D.M.’s “caveat”. Gotta have some skill to live up to your equipment, and highpower is a demanding pursuit.

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