Build template
MK12 SPR
Special Purpose Rifle accuracy from a parts build
The MK12 SPR is a modern take on the Special Purpose Rifle for the intermediate builder who wants distance accuracy in a rifle that still fights like a carbine. It centers on a Sons of Liberty Gun Works Precision SPR barrel in .223 Wylde, a LaRue MBT-2S two-stage trigger, and a Vortex Razor 1-6x LPVO standing in for the classic SPR glass, all on Aero Precision receivers with a free-float rail.
This is a parts build that requires assembly or a gunsmith, tuned for accuracy over ultralight handling. The SPR-contour barrel adds rigidity for tight groups, the two-stage trigger gives a predictable break from field positions, and the free-float Midwest rail keeps barrel harmonics consistent shot to shot. It keeps a fightable weight while prioritizing precision at range.
Every part below shows its current price, and you can load the whole configuration into the builder in one click to compare parts, confirm fitment, and see the total move.
Host platform
Parts build: the receivers and barrel are line items in the list below, so there is no complete rifle to buy first.
Why this build
The barrel is the whole argument. The SOLGW Precision SPR is a 16-inch .223 Wylde barrel with an SPR contour, mid-length gas, a 1:7 twist, and 5/8x24 threads. The .223 Wylde chamber is the key detail: it shoots both .223 and 5.56 accurately, and the 1:7 twist stabilizes heavy match projectiles up to 77 grains, which is what an SPR is built to shoot. The heavier SPR contour adds the rigidity that turns good ammo into tight groups without the dead weight of a bull barrel.
The LaRue MBT-2S is the trigger that lets the barrel show its accuracy. It breaks at 4.5 pounds across a 2.5-pound first stage and a 2-pound second stage, machined from S7 tool steel, the same material Geissele uses. A clean, predictable two-stage break is what makes a precision rifle repeatable from field positions, and the MBT-2S delivers that at a fraction of a premium trigger's price. It includes a heavier 6-pound spring if you want a more deliberate pull.
The Vortex Razor HD Gen II 1-6x brings the glass. Its APO lens system eliminates chromatic aberration, the true 1x low end keeps close targets fast with both eyes open, and the JM-1 BDC reticle gives holdovers for the 5.56 the SPR is optimized around. A 1-6x LPVO is the modern SPR answer: it covers close-to-far in one optic, so the precision barrel is usable at speed and at distance without swapping glass.
Parts list
Upper Receivers
$128.24 at Optics Planet · Out of stock
The Aero Precision M4E1 stripped upper is a forged 7075-T6 receiver with a strengthened barrel extension interface for a tight barrel fit, which matters on an accuracy build. M4 feed ramps and standard compatibility make it a clean foundation for the SPR barrel and free-float rail.
Lower Receivers
$155.00 MSRP
The Aero M4E1 stripped lower simplifies assembly with its threaded bolt catch pin and removes upper-lower play with a tension screw, giving a more rigid, consistent platform for a precision-oriented rifle.
Barrels
$399.00 at Optics Planet · In stock
The SOLGW Precision SPR is a 16-inch .223 Wylde barrel with an SPR contour, mid-length gas, 1:7 twist, and 5/8x24 muzzle threads. The .223 Wylde chamber delivers match accuracy with both .223 and 5.56, and the SPR contour adds rigidity for tight groups while keeping practical field weight. The 5/8x24 threads accept precision brakes and many .30-caliber muzzle devices.
White Oak's 18-inch SPR barrel is the more authentic classic MK12 length, squeezing more velocity from heavy match loads at the cost of a bit more weight.
The Criterion CORE stainless mid-length is an accuracy-focused barrel at a lower price if the SPR contour is more than you need.
Handguards
$188.95 at Optics Planet · In stock
The Midwest Industries Combat Rail free-floats the SPR barrel, which is essential for consistent harmonics and accuracy. Seven M-LOK faces, a full-length top rail, and a lifetime warranty come at a price well below premium rails, leaving budget for the barrel and optic.
Bolt Carrier Groups
$223.99 at Optics Planet · In stock
The BCM bolt carrier group is a full-auto M16 profile with a shot-peened C158 bolt, chrome-lined interior, staked gas key, and enhanced extractor, all HP/MPI tested. It is the reliable, mid-priced carrier that keeps a mid-length gas gun running without adding cost that belongs in the barrel.
The Daniel Defense M16 BCG offers the same carrier used in DD complete rifles with a heavier finish package.
Charging Handles & Action Controls
$79.79 at Optics Planet · Out of stock
The BCM Gunfighter charging handle's Mod 4 extended latch and reinforced internal design make press-checks and manipulations easy under a mounted LPVO, at a value price.
The Radian Raptor-LT adds ambidextrous 1.2-ounce latches for easier operation under the scope.
Triggers & Fire Control
$134.99 at Optics Planet · Out of stock
The LaRue MBT-2S is a two-stage trigger machined from S7 tool steel, breaking at 4.5 pounds total across a 2.5-pound first stage and a crisp 2-pound second stage. Its clean, glass-smooth break and fast reset make it one of the best values in a precision AR trigger, and it includes a heavier 6-pound spring for a more deliberate pull.
The Geissele SSA-E offers a lighter, even more refined two-stage break for shooters chasing the last bit of precision.
Pistol Grips
$18.90 at Optics Planet · In stock
The Magpul MOE-K2 uses a steeper 17-degree angle that supports a modern stance and steadier hold from field positions. It is a value-priced polymer grip that fits the accuracy-first budget of this build.
Stocks & Braces
$59.95 at Optics Planet · In stock
The Magpul CTR is a lightweight 8.8-ounce stock with a friction lock that eliminates wobble, giving a solid, repeatable cheek weld for precision work without adding weight.
The B5 Enhanced SOPMOD adds a wider cheek weld for more consistent head position behind the scope, plus battery storage.
Optics & Sighting
$1,469.00 at Optics Planet · Out of stock
The Vortex Razor HD Gen II 1-6x24 is a premium LPVO with an APO lens system that eliminates chromatic aberration, true daylight-bright illumination, a forgiving eyebox, and a JM-1 BDC reticle matched to 5.56. It gives the SPR barrel usable precision to distance while keeping true 1x speed up close, and the Gen II-E variant trims weight to 21.5 ounces.
The Primary Arms SLx 1-6x Gen IV with the ACSS Nova reticle delivers most of the capability at a fraction of the cost.
The Nightforce ATACR 1-8x adds magnification and first-focal-plane precision for the shooter pushing the SPR to its accuracy limit.
Magazines & Feeding
$13.95 MSRP
The Magpul PMAG 30 Gen M3 is the industry-standard 30-round magazine, with a four-way anti-tilt follower and constant-curve feed path for reliable feeding of the match ammo this build is meant to shoot.
Current build cost $2,871.76
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Capability profile
Capability Scan
Baseline vs Configured
Frequently Asked Questions
▶Why a .223 Wylde chamber on the SPR barrel?
▶Can I build this MK12 SPR cheaper?
▶What is the difference between a 16-inch and 18-inch SPR?
▶Do the 5/8x24 threads limit my muzzle device options?
Keep reading
- MK12 Build Guide 2026: SPR Clone & Modern 18-Inch Parts List
- Best Military Clone Builds 2026: MK18, Block II, URGI & Spear LT Parts Lists
- Best AR-15 Triggers 2026: Geissele vs LaRue vs ALG Compared
- Best LPVO for AR-15 2026: Vortex vs Trijicon vs Primary Arms
- Best AR-15 Barrel Length: 14.5 vs 11.5 vs 16 Compared
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