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Plumb Precision: P3-A & the Next Generation of Steiner

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From pistols, tactics, calibers, platforms, to even an entire branch of service, the last several years of the U.S. Military is filled to the brim with new and shiny, alongside some novel kinks to work out. 

Some may question the reasoning of revamping our armed forces seemingly from the ground up immediately following the official end of two decades of war, but frankly, this is all happening at the best time possible. 

History is rife with valid complaints of those in the dirt being indistinguishable from harried lab rats when it comes to experimental testing (with war comes innovation), and if we can discover and amend our mistakes during high-intensity training before putting the lives of ours literally on the line, all the better.


In 2020, the Department of Defense launched several new weapons development programs to increase lethality, and one still ongoing is the Medium-Range Gas Gun (MRGG or “Margie”). 

The MRGG is broken into two parts: the MRGG-S (“Sniper Support” to life cycle out the FN SCAR Mk20) and the MRGG-A (“Assaulter” or commonly called “Assault” to replace the role of the FN SCAR Mk17), with this article covering an entry into the latter category.

Chambered in 6.5 Creedmoor, these semi-automatic rifles will provide both greater precision and longer potential envelopes of engagement for those on the ground, especially at the small-and-special unit level. 

6.5 Creedmoor (Hornady 140gr ELD-M), left vs .308 Winchester (M118LR), right

Among the requirements for the MRGG-A are M4-like controls, accuracy of no worse than 1 MOA with issued 140-grain XM1200 ammunition, and a weight threshold of 10.5 pounds, with 9 pounds being considered ideal.

In the world of weapons, “assault” is synonymous with “small,” so barrels worn by MRGG-A applicants are much shorter than those traditionally used with 6.5CM. How short? Several contenders are rolling with 14.5-inch barrels, and the one in this article has a 14.1-inch barrel, nearly a full 2 inches lopped off of the shortest we’ve built ourselves (see RECOILweb). 

Of course, there are those who’ll say, “What a waste! Why not just use [insert short barrel caliber of choice]?” To which we say two things: caliber commonality matters for logistics and tell it to your congressman.

The word “assault” is a clue here. The MRGG-A is intended to be used up close and personal but also have the capability to engage at longer distances if need be. While the internet argues about the best rifle/ammo/optic for a given situation, the DoD is spending that time searching for solutions with overlapping envelopes of use.

There are some lessons and experience from the SCAR Mk17 program at play here, too. 

When SOCOM members were given the choice between a 16-inch barrel and a 13-inch barrel on a Mk17, the shorter barrel was almost universally the choice despite being chambered in 7.62. Man-sized targets out to 800 yards aren’t a problem with that setup, provided that you have enough magnification to see and skill on the trigger. 

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The only reason we don’t see the same in the American civilian market is solely due to antiquated regulations on minimum barrel lengths, passed because lawmakers at the time knew they couldn’t outright ban all pistols.

Using shorter barrels with calibers traditionally meant for longer distances is nothing new, likely predating the hacksaw. All a shorter barrel really costs you (within reasonable limits) is reduced velocity. While shooting rifles well outside their intended range requires a little math and is a bit more challenging, it’s certainly doable. 

We’ve demonstrated it ourselves on many occasions (see our 14-inch 7.62×51 SCAR Mk20 in Issue 55, the 11.5-inch 6ARC AR in Issue 51, or RECOILweb for 10.3-inch 5.56 SBRs at 1,000 yards). It’s even easier with the MRGG-A’s 6.5 CM chambering, as it has a very flat ballistic arc.

6mm arc outfitted
LANTAC 6mm ARC, 11.5″ barrel. This isn‘t a precision rifle capable of a combat role. This is a combat rifle capable of precision.

The rifle shown in this article is a collaboration between Plumb Precision Products (P3) and CheyTac USA. It was submitted for the MRGG-A solicitation but wasn’t down-selected by SOCOM for further testing. We’ll break down this rifle and show you how you can make one for yourself, as well as detail some additional features not seen on this model but which was developed.

The Steiner M8 DFP optic, so new it’s not yet listed in their catalog at the time of this writing, already has some special unit contracts overseas. It’s but the first of a new series, and we’ll show you what it’s about and what comes next. The sample you see here today came directly from a special unit evaluation, and the DoD has their eyes on this one. Read on to see why.


The official name of the rifle is “CT-10 6.5CM for MGSS-A.” If it sounds like it came off a PowerPoint presentation, that’s because it did. We’ve removed the contract-ese and simply dubbed it the P3-A, a nomenclature approved by Plumb Precision.

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When fully stripped, the generous profile of the 14.1-inch barrel is plain as day.

The receivers themselves are large-frame AR made by CheyTac. They’re cut to the DPMS pattern and compatible with 7.62x51mm SR-25 magazines. Though these magazines were once rare and expensive in this format, Lancer Systems and Magpul spackled in that gap and any well-equipped LGS has them on the shelf.

The controls on the P3-A are excellent and what we’ve come to expect from an AR-variant that even feigns being high-end or specialized: it’s actually fully ambidextrous. 

All manipulations can take place on either side of the rifle — charging, manipulating the safety, dropping the magazine, and both locking and releasing the bolt. Though it would be nice to see a short-throw selector, importantly the ambidextrous selector on the right side doesn’t dig into the trigger finger on those who use a high hold, a harder feat than you might expect.

The bolt lock/release is from Blue Teal Bravo (learn how to install one yourself in RECOIL Issue 52 or in 

RECOIL’s DIY Guns). The ambi charging handle is the Geissele SCH, which is in the Goldilocks zone for size.

There’s also a forward assist, which CheyTac doesn’t put on their own large-frame receivers but included here as it was a MRGG-A requirement.

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The ambidextrous selector is both eminently usable and low-profile, without scraping or cutting the trigger finger.

For furniture, a B5 SOPMOD takes up the rear, attached to a LAW Tactical folder to really decrease the overall length for transport. No, you can’t shoot it folded (not more than once) but that’s not an actual problem outside of awful ’80s action movies. The grip is from BCM and more upright than a traditional AR grip.

The standard trigger on the P3-A is the straight bowed, two-stage Daniel Horner Signature Trigger from Timney, effectively combining up-close-and-fast with precision potential. Our example is wearing a Timney Targa, also two-stage with a straight bow.

The barrel is from Ballistic Advantage. Turned from 416R with a 1/8 twist rate, the profile is generous for stiffness and adds to the heft of the P3-A despite being just a hair over 14 inches.

The muzzle device is a P3MB; we know what you’re thinking — it looks like a Lantac. 

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The standard P3-A will have a Timney Daniel Horner Signature trigger, and this example is wearing a Timney Targa Two-stage.

We can’t disagree on that. P3 tells us it was specifically designed to remain offset from the muzzle crown to ensure accuracy and not impart any harmonic disturbance, one of the last long-range bogeymen. Permanently attaching the P3MB brings the short 6.5CM barrel comfortably within the legal limit to 17 inches. 

Aesthetics aside, despite the multi-chamber brake and the P3-A being a 14-inch Creedmoor, it wasn’t as loud as expected (though still very loud) and combined with the weight made for a surprisingly pleasant shooter.

The anti-rotational handguard has a continuous Picatinny rail along the top and M-LOK cuts along the bottom and sides. Though this example uses a wedge to lock everything down with dual Torx fasteners, P3 made a version with a toolless quick-change barrel through the use of an interrupted thread system. Sitting under handguard is a low-pro gas block, to be replaced in the future with a P3 adjustable.


Adorning the handguard are Kriss USA Defiance iron sights, Magpul handstops, and a P3 carbon-fiber heat shield that closely hugs the lines.

The whole shebang is Cerakoted by BlownDeadline, which has been producing high-quality work for years. It’s no different on the P3-A.

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The Mk4 Battlelight is dual fuel and comes standard with a push-clicky/remote switch tailcap.

For a weapon-mounted light, the P3-A came with a Steiner Mk4 Battlelight. With a mere 500 lumens, it’s dual fuel and eats from a pair of CR123s or a single 18650 battery. The tailcap has both a push/clicky button as well as a port for remote switches.

Even when you have a low-power variable optic (LPVO) with a 1x setting, there’s still an advantage to having an offset or piggybacked dot sight for use in unconventional positions or for use with night vision (see RECOIL Issue 62). Though originally designed with pistols in mind, the Steiner MPS in an offset mount excels at that role.

Speaking of optics, inside that Spuhr SP-4008 mount (a cantilever QDP-4016 would probably be better on this gas gun) is the new Steiner M8 DFP.


Despite what the internet declares, LPVOs are hardly the end-all optic (see RECOIL Issue 51). Second focal plane (SFP) optics don’t have a reticle that scales with magnification, meaning that any ballistic or MIL-Dot markings are only valid at maximum magnification. That said, a dot or other source of illumination is easier to make daylight bright to better mimic a traditional dot sight. 

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Our example of the Steiner M8 Dual Focal Plane (DFP) is wearing an M8Xi body and mounted in a Sphur SP-4008.

Front (or first) focal plane (FFP) optics do have reticles that scale with magnification, making them more useful between powers (especially important with optics that go above 6x) but are very difficult to make bright unless you’re into giant fuzzy blobs.

In their new optic, Steiner splits the difference. As you no doubt surmised by the name, it operates in both focal planes. The “dot” portion of the reticle stays static in the second plane, while the ballistic reticle remains true regardless of the magnification level used.

But it’s more than just a dot slapped on top of plain crosshairs or MIL-Dot reticle. Inside the M8 DFP is the latest caliber-agnostic version of the Plumb reticle, first reviewed back in RECOIL Issue 35.

With the DFP optic, the illuminated red portion stays the same size regardless of the magnification while the ballistic tree scales.

Designed around common target sizes, the Plumb reticle is intended to rapidly range and engage both up close and at distance, all without the need for special calculations, a slide rule, or using an app on your phone.

The FFP portion of the scope isn’t illuminated but, in a pinch, can still be used due to thick pointers on three sides that completely disappear at higher zooms. The inner funnel is sized to a target in profile, and the outer one 20 inches, or shoulder width, when head-on.

In addition to fast engagement, the FFP reticle has the normal MIL markings for traditional ranging as well as a Christmas tree of wind holdover points.

This Plumb reticle is zeroed at either 100 yards or 100 meters, whichever you’re used to. To be as universal as possible among both branches of services as well as nation-states, the left side is marked in yards and the right in meters (with a handy reminder at the bottom in case you forget).

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The bullet drop compensator is a blend of four common ballistic patterns that most closely matches 140-grain XM1200 6.5 CM. What this really means is that you should take your setup out and test it for yourself, which we’ve long advocated with any BDC-style reticle.

Plumb reticles have never been made to serve bench shooters looking for small groups on paper but instead those seeking effective hits on target. Specifically, this is a combat optic that maxes out at 8x, intended to keep all rounds within a 9-inch circle at 800. 

In terms of the scope itself, our example of the 34mm M8 DFP has 1/10 MIL adjustments sitting under capped turrets. Caps are yet another thing to lose, but outside of achieving a zero the turrets are meant to be untouched when paired with a Plumb reticle.

There are 11 illumination settings on the left side with “off” stops in between. The diopter adjustment is generous; while Steiner lists the M8Xi with an eye relief of 3.54 inches, our example was usable at max magnification a full inch further from the eye.


The M8 DFP is but the first version of this scope to come from Steiner. The next model has Steiner’s integrated smart IFS (Intelligent Firing System), which projects a heads-up display onto the second focal plane, not only placing the reticle where it needs to be to hit given automatic environmental and range inputs, but also changes the funnel shape and arcs themselves for your given rifle/caliber combination.


Once you get into larger calibers, there are guns that are easy to carry and guns that are fun to shoot, with very few rifles in the intersection of that Venn diagram.

There’s no getting around it, the P3-A is high density. Ten pounds and 2 ounces doesn’t have to feel like a lot with more overall length, but once that stock is folded you definitely know it’s there. Add a full magazine, scope, mount, sling, flashlight, offset dot, control accessories, and other accoutrements, and it’s not hard to tack on the pounds. Fully gassed and outfitted as shown here, you’re toting 14 pounds, flat.

When we think of precision, a heavier barrel normally comes to mind. And indeed, the Ballistic Advantage pipe significantly adds to the weight of the package. If this rifle were to have a forever home in our safe, we’d seek out some fluting or similar weight savings.

The only way the P3-A was guaranteed to go into production was if it won the contract, but as that didn’t happen its future is in flux. If Plumb Precision and CheyTac give it a quick diet, it’s an easy-button even over the bevvy of 6.5 CM bolt guns. Even more so if the Plumb skunkworks quick-change barrels and adjustable gas blocks are tossed into the mix. But even if they don’t, there’s enough ideas and detail in this article to allow you to roll your own Margie contender yourself, right at home.

The Steiner M8 DFP with the latest Plumb reticle is one of the most thoughtful designs we’ve ever seen in this format. While there are some minor gripes, the clarity and larger-than-advertised eye box combined with the functionality of the dual focal plane and the reticle itself are well worth it. And when IFS is added? Look the hell out.

Just within the last several years, fresh DoD requests and solicitations for Big Army have given us in the civilian world a lot of great new options. And MRGG, specifically the MRGG-A portion, brings a whole new level of capability and forces reconsideration of what is “true.”

After all, it wasn’t that long ago 7.62 NATO was considered ideal for long-range, short barrels were only for CQB, and 6.5 Creedmoor was best in bolt guns. No more, and Good Riddance. 


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The P3-A is just over 26 inches with the stock folded.

Plumb Precision Products / CheyTac USA P3-A

  • Caliber: 6.5 Creedmoor
  • Barrel Length: 14.1 inches
  • Overall Length, Stock Open: 35 to 38.5 inches
  • Overall Length, Stock Folded: 26.5 inches
  • Capacity: 10, 20, 25
  • Weight (unloaded): 10 pounds, 2 ounces
  • Weight (loaded and as configured): 14 pounds
  • URL:,


  • Steiner M8 DFP TBD
  • Mk4 Battle Light $432
  • Steiner MPS $575
  • Spuhr SP-4008 mount $410

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