INTRODUCTION:
A Sterling Arms International (SAI) R18 Mk3 Pre-Production 5.56mm semi-automatic Test Rifle caused quite a positive stir amongst those Canadian Gunnutz fortunate enough to attend the annual TACOM show earlier this month in Ontario. The rifle’s svelte lines and Hard-Coat Anodizing with painted pictogram markings evoked comparisons to the appearance of Heckler and Kock products, among some show attendees, which was quite a compliment. One can only hope that the new rifle from SAI performs as good as it looks in terms of reliability, accuracy and high-round-count durability. This initial pre-firing inspection will provide details of the changes and improvements made to the rifle while offering up some experience-based impressions and observations. A Part 2 will be published at a later date in which the results of test-firing will be discussed in terms of accuracy achieved and the reliability experienced. While by no means exhaustive, these two Reviews ought to give the curious, prospective customer a jump-start in learning about the R18 Mk3 and the benefits that it brings to the table for Canadians in search of a modern utility and sporting rifle.
DISCLAIMER
I am friends with the Chief Designer of the R18 series of modern sporting and utility rifles, Mr. James R. Cox – who also happens to own “The Shooting Edge” Indoor Range and Gun Shop in Calgary, and a similar set-up called “Target Sports” in Gormley, Ontario. “JR” as he likes to be known, has entered into a business arrangement with SAI who are responsible for the manufacture of the rifles to be marketed in both Canada and Internationally with a strong secondary focus on international markets. The R18 Mk3 represents a significant change to the manufacturing process for the new firearm, taking advantage of low workforce wages in other nations to manufacture superior parts and assemblies on robotic Computer Numerically-Controlled machinery to exacting international ISO standards in order to improve the product, hold tighter tolerances, incorporate superior materials and perhaps most important – reduce the MSRP by 30% from $2700 CAD to a mere $1800 CAD! The R18 Mk3 will rely upon overseas component manufacture with Canadian assembly and Quality Control checks (to include test-firing). Although supply chain issue could complicate production and sales timelines, there is no disputing the cost savings associated with the move to offshore manufacture. It simply had to be done in order to keep costs reasonable for the R18 Mk3 customer base. Once production ramps up to full capacity the projected output (subject to change) will be 200 rifles per month.
Notwithstanding my positive relationship with the rifle’s Chief Designer and my role as a consultant during preparation of the FRT Submission, it is my intention to provide a non-biased Review of the R18 Mk3, perceived warts and all (if any). To do otherwise would compromise my integrity and perform a disservice to the members of this Discussion Forum, which is never my intent.
DESCRIPTION
The R18 Mk2 is a short-stroke, gas-operated, shoulder-controlled, semi-automatic, modern sporting and utility rifle that is assembled and test-fired in Canada. It makes use of a Carbine-Length Gas System and a properly stress-relieved Medium-weight Barrel in order to reduce Barrel-whip, enhance the rifle’s balance and to reduce overall weight by over ½ lb. The Mk3 continues to make use of standard, AR15 STANAG Magazines, having been design-finalized prior to 15 December 2023, the coming into force date for Bill C21. The Mk3 features a Melonite-lined Chamber and Bore, as well as a stainless steel Piston, Rod, Bolt and Cam Pin for corrosion resistance and ease of maintenance.
Ejection Port with stainless steel Bolt, Dust Cover and Cartridge Case Deflector
TECHNICAL SPECIFICATIONS
| Name | R18 Mk3 | R18 Mk2 |
| Caliber | 5.56 mm ( 7.62×39 mm, .300 Blackout to follow) | .223 Wylde |
| Barrel Material | AISI-SAE 4140 CrMo4 Steel | AISI-SAE 4150 CrMo4 Steel |
| Barrel Finish | Exterior – Matte Black Gas Nitride Interior – Melonite | Gas Nitride |
| Receiver Material | 7075 T6 Aluminum Alloy | 6061 T6 Aluminum Alloy |
| Muzzle | 1/2-28 TPI Threaded | 1/2 – 28 TPI Threaded |
| Muzzle Device | SAI 5.56mm Muzzle Brake | Various |
| Dust Cover | Plastic – Strike Industries Clip on style | Nil |
| Magazine Capacity Options | Fits standard 5 round STANAG magazines | Fits standard 5 round STANAG magazineS |
| Brass Deflector | Bolted on Upper Receiver | Milled on Upper Receiver |
| Barrel Length | 18.6 ” (472mm) | 18.6 ” (472 mm) |
| Buttstock Attachment | 1913 Picatinny – 3 slot with QD Sling Swivel port | 1913 Picatinny – 3 Slot |
| Total Length (Without Stock) | min. 28.7” 730 mm | N/A |
| Total Length (With Stock Collapsed) | min. 37.8” 960 mm | min. 37.75″ 95.88mm |
| Total Length (With Stock Extended) | 40.8” 1037 mm | min. 40.7″ 1035mm |
| Weight (Without Stock) | min. 3120 gr (6.38 lb) | N/A |
| Weight (With Stock) | min. 3620 gr (7.97 lb) (Without Magazine) | min 3730 gr (8.3 lbs) (without Magazine) |
| Weight of Stock | min. 500 gr (1.1 lb) | Min. 500 gr (1.1 lb) |
| Method of Operation | Short-Stroke, Gas Piston action, Rotating Stainless Steel Bolt, Locking Head | Short-Stroke, Gas Piston action, Rotating Bolt, Locking Head |
| Type of Piston System | Carbine Length, Stainless Steel Piston and Rod | Rifle Length |
| Mode of Operation | Semi- Automatic ONLY | Semi- Automatic ONLY |
| Fire Selector Position | Left Side Only | Ambidextrous |
| Trigger Pull Force | 3.5 lb Single Stage Cartridge type (TriggerTech) | 3.5 lb Single Stage Cartridge type (TriggerTech) |
| Mechanical Safety | Firing Pin Safety on Bolt Carrier | None |
| Height | approx. 7.76” (197 mm) | approx. 7.76″ (197mm) |
| Width (without charging handle) | approx 2.16” (55 mm) | approx 2.25″ (58 mm) |
| Accuracy (5.56mm) | 2.5 MOA with commercial high quality ammunition | 2.5 MOA with commercial, high- quality ammunition |
| Muzzle Velocity | Minimum 928 m/s (3225 ft/s) with Standard 55gr M193 Ball 5.56mm ammo. Data to be added once testing in alternate calibers is completed | Minimum 825 m/s (2700ft/s) with Standard .223 Rem 55gr ammo |
| Barrel Profile (5.56mm) | 1:7” 6 grooves right hand twist, “Medium” profile | 1:8′ 6 grooves right hand twist |
KEY IMPROVEMENTS (Mk2 to Mk3)
External Finishes. The Mk3’s T7075 Receiver is finished in Mil-spec Type 3 Hard-coat Anodizing. The Barrel’s exterior is a matte Black Nitride (Gas Carburization) process.
Barrel. The 18.6” Barrel is now manufactured from AISI-SAE4140 CRMo4 Steel, vice 4150 steel, with a durable Melonite-lined Chamber and Bore for longevity. The Mk3 Barrel is manufactured with a 1:7”, 6-groove, Right-hand twist, vice 1::8” in order to better stabilize a broad range of bullet weights and styles. The Barrel is fitted with a proprietary SAI Muzzle Brake whish resembles a standard Birdcage Flash-Hider but which reduces muzzle jump and perceived recoil. The Mk3 Barrel is Medium profile, in order to maintain a reasonable weight while improving the rifle’s balance.
Mk3 Muzzle Brake, Barrel and Gas System (Handguard Removed)
Barrel Nut. The Barrel Nut is designed along the lines of the HK 416/MR556 Barrel Nut, with a groove to accept the Locking Bolt which secures the Handguard to the Nut. At this time, the Sterling’s Barrel Nut is slightly too large to accept HK Handguards such as the Geissele URX.
Gas System. The Mk3 makes use of a short Short-stroke, Carbine length Gas System instead of the Rifle Length system found on the Mk2. This results in lighter overall weight, improved balance with the center of balance right in front of the Magazine Well, and reduced Barrel-Whip for improved accuracy. The Mk3 uses a self-regulating Gas System consisting of a conically-shaped Gas Block interior and matching Piston exterior shape. When fully-nested at rest in the Gas Block, the conical, stainless steel Piston is tight against the inside of the Gas Block and seals a Vent-Hole in the front of the Block. Once the diverted gas from a fired cartridge jets up the Barrel’s Gas Port and strikes the Piston, the Piston is forced sharply rearwards will all of the force necessary to fully cycle the rifle’s action. As the Piston and Rod move rearwards striking the Bolt Carrier and driving it backwards to unlock the bolt and extract/eject the fired cartridge, the Piston unblocks the Vent Hole so that excess gas can escape forwards underneath the Handguard. The conical shape of the Piston and interior of the Gas Block ensures that excess gas vents exponentially. This in turn ensures that the Mk3 can never be over-gassed, regardless of the type of ammunition fired. The system “sips” only what it needs to reliably cycle the action. As the rifle becomes fouled through use or exposure to extreme environments, the Gas System simply “sips” more gas to force the Piston and Rod rearwards with appropriate additional force. This self-regulating system was adopted from the HK SL8 and the G36 service rifle. The Gas Block is now secured to the Barrel with Two straight Cross-Pins while pressed up against the Barrel’s Gas Journal Shoulder.
Mk3 Gas System Disassembled
Handguard. The Handguard contour has been adjusted into an oval cross-section rather than circular. This provides a narrower grip while maintaining clearance around the Barrel and Gas Block/Piston Rod. The Handguard features Seven columns of MLOK Slots, positioned at 2, 3, 4, 6 , 8, 9 and 10 O’Clock for the attachment of mission essential equipment.
Receiver Alloy. The Receivers are manufactured from stronger T7075 aluminum alloy, as opposed to the softer T6 6061 alloy used on the Mk2. The use of the stronger alloy permits lighter weight components manufactured from a thinner thickness of material.
Receiver Design. The Receiver halves have been redesigned to be thinner and lighter weight on the Mk3. The Upper Receiver in particular, has been redesigned to be more streamlined and less “block-like” in appearance. There is now a protective Rib around the Right Side Magazine Release to assist in preventing accidental release of the STANAG Magazine. The Upper Receiver features a steel insert at the forward end which both lines the Gas Piston Rod’s path through the Receiver (steel on steel) and provides a threaded steel hole for the Handguard’x Top Indexing Screw. Note that the Top Indexing Screw (2.5mm Hex), is not essential for Handguard retention nor indexing. In the case of long optics which cover the Indexing Screw, the screw may be omitted without undue concern. The Lower Receiver features a spring-loaded Pin in its Rear area that presses upwards against the underside of the Upper Receiver’s Rear Lug, eliminating Receiver slop and stopping any rattling.
Magazine. The Mk3 ships with a polymer NATO STANAG AR15-pattern 5-round Magazine.
Dust Cover. The Mk3 is fitted with a Strike Industries, AR15-compatible polymer Dust Cover.
Empty Casing Deflector. The Empty Casing Deflector permitting Left-hand firing is now Bolted onto the re-contoured Upper Receiver.
Pistol Grip. The Pistol Grip is a rubber-coated affair with ambidextrous Thumb rests and an internal storage compartment accessible through the bottom of the Grip.
Trigger. The Mk3 uses a TriggerTech “Duty” Trigger with a crisp, fixed, single-stage 3.5lb pull. The Mk3 will also accommodate a mil-spec Trigger Mechanism without issue, suggesting that Geissele Triggers and other Cassette type AR15 Triggers ought to function fine (subject to confirmation).
Mk3 Lower Receiver Showing Spring-Loaded “Anti-Rattle” Pin, TriggerTech “Duty” Trigger and One-Piece Ambidextrous Bolt Catch/Release
Bolt Catch/Release. The Mk3 features new, integral, ambidextrous Bolt Catch and Release Lever on the Right side of the Receiver as well as the typical AR-style Paddle on the Left Side. The Lever and Paddle are a single piece which allows the Trigger Finger of a Right-handed firer to engage or release the Bolt Catch. This design feature was lifted from the HK MR223.
Charging Handle. The profile of the Charging Handle has been changed from a round “barrel”-style of Handle to a convex, curved “Trigger” style which is considerably more comfortable. The Charging Handle is non-folding at the present time. The Charging Handle remains non-reciprocating and is secured forwards by a Rare Earth Magnet.
Mk3 Non-Reciprocating (and Non-Folding) Charging Handle
Unitized Bolt/Carrier Assembly. The Bolt, Bolt Carrier, Operating Springs and Guide Rods are now removed from the rifle’s Upper Receiver as a single, captive assembly. Further disassembly into the component parts is a simple matter, however the assembly remains together unless deliberately broken down. This concept was taken from the SIG MCX and greatly eases the Field Stripping and Reassembly procedures. The Bolt Carrier Assembly contains the greatly thinned-down Bolt Carrier itself, two steel Guide Rods, an Operating Spring on each Rod, and a Rear Locking Piece which holds the entire assembly together. The Bolt Carrier runs on the Steel Guide Rods and broad contact with the interior Receiver Walls. The Bolt Carrier’s exposed face has 2 indents which are designed to allow operators to use their Thumb or a Cartridge Case to push the Carrier home, fully into battery in the event of a dirty chamber.
Mechanical Safety. This mechanism physically prevents the Firing Pin from contacting the primer of a live cartridge unless the Bolt is fully rotated into the locked position with the Cam Pin rotated to the side of the Bolt Carrier. This feature was lifted from the SIG MCX Bolt Assembly.
Buttstock. The polymer Buttstock weighs 1.1lbs (.5 kg) and is of the Sliding/Collapsing design with a QD Sling Loop feature and 6 sliding Length of Pull settings. Any other Buttstock with a Milspec Tube diameter or a Picatinny attachment style may be substituted for the Factory sliding Buttstock, including many folding options. The Picatinny Buttstock attachment provides Three slots to choose from, providing a limited range of vertical Buttstock adjustment. The Milspec Buttstock Tube is removable from the Lower Receiver with the press of a single button located on top of the Tube. The Picatinny Buttstock attachment system was borrowed from the SIG MCX rifle.
Mk3 Buttstock With Release Button
Weight. The Mk3’s weight has been significantly reduced from 8.5 lbs to 7.97 lbs (3.62 Kg) with the removable Buttstock, but without a Magazine.
Dimensions. The Mk3 is approximately 1/2” thinner in Width than the Mk2, producing a “cleaner”, more streamlined and svelte firearm.
Accuracy. 2.5 MOA (maximum) at 100m (2.5” 10-round group size with declared flyers). Subject to live-fire confirmation in Part 2 of the Review.
Price. Offshore manufacture and finishing of the major components has allowed production cost-savings to be passed directly to the consumer in the form of a 33% price reduction. That is correct, whereas the domestically manufactured R18 Mk2 retailed for $2700 CAD, the product-improved and Canadian-assembled and tested Mk3 will initially sell for just $1800 CAD. Obviously price fluctuations in raw materials, wage increases and general inflation will eventually drive modest price increases as is the case with all consumer goods.
HANDLING
The Mk3’s balance point is directly in front of the Magazine Well, which makes for ideal weight distribution when carrying and shouldering the new rifle. When equipped with “iron sights”, the Mk3 feels very lightweight and quite lively in the hands. It is quick to point and thanks to the familiar AR15-style ergonomics is comfortable and natural to point at a target. The cheek-weld and head-height are both excellent for both Irons and Optics and can be further adjusted up or down using the 3-slot Picatinny Rail on the Rear of the Lower Receiver.
The Mk3’s action slides very smoothly on two steel Guide Rods nestled within the top of the Upper Receiver. Each of the Rods “guides” an Operating Spring, the combined force of which closes the Bolt Carrier forward against the Barrel Trunnion with the rotating Bolt locked into the Barrel Extension. The curved Bolt Carrier body is guided during its back and forth movement by the matching curved Receiver Walls. The Bolt is hardened Stainless Steel with a single Ejector and a standard AR15 Extractor. The Rotating Bolt is controlled by an AR15-style hardened Stainless Steel Cam which follows a slot in the Bolt Carrier to lock and unlock the rifle’s action. Over-pressure Proof rounds are fired as part of the pre-shipping Quality Control checks and inspections.
Mk3 Bolt Carrier Assembly Riding Inside of Upper Receiver
FIELD STRIPPING AND REASSEMBLY
Very much like its Mk2 predecessor, the R18 Mk3 readily strips down for basic field maintenance without the use of tools. The exception to this is access to the Gas System beneath the Handguard, which requires a 5mm and a 2.5mm Hex Wrench to remove the bottom Bolt and a top Retaining Screw respectively. Field stripping is very intuitive and the rifle has been designed in such a way that the working components can only be assembled in the correct sequence and position. New or inexperienced owners are encouraged to refer to the Owner’s Manual (to be issued on-line) for specific instructions and the recommended sequence of stripping and reassembling the Mk 3.
The Mk3 Field-Stripped for Maintenance
Detail Strip of Captured Bolt Carrier Assembly
MAGAZINE COMPATABILITY
The following magazines were inserted into the Mk3 with an open Bolt to ensure proper fitment without over-travel. All magazines tested (less the ETS Gen2) dropped free when the Magazine Release was activated:
– Magpul PMag Gen 3 5/30
– Magpul PMag Gen 3 5/20
– Lancer AWM 5/30
– MFT “Pistol” 10/10
– ASC “Pistol” Mag 10/20
– ASC “Pistol” Mag 10/30
– Thermold CAF 5/30
– CAF Sterile/Generic Aluminum 5/30
– USGI Surefeed 5/30
– ETS Gen 2 5/30
– CZ Bren 2 5/30
– Surefire 5/60
RECOMMENDATIONS FOR FURTHER ENHANCEMENT
It is recommended that SAI make the R18Mk3 as ambidextrous as possible, thereby catering to Left-handed firers at no additional expense to the purchaser. This can be accomplished inexpensively and relatively easily by:
- Install a Norgon-style Ambidextrous Magazine Release
- Install a Right Side Selector Lever
In addition to the above, it is recommended that SAI consider the following based on initial customer feedback:
- Incorporate a Folding Charging Handle so that it lies flat against the rifle when folded.
- Offer the Folding Buttstock adapter demonstrated in the ADKAS “SAM” video “The SIG MCX we have ar home” on YouTube as a standard feature.
- Eliminate the small, Top Indexing Screw for the Handguard completely, but leave the Picatinny Indexing Tab. The screw is entirely superfluous and cannot be accessed when the rifle is fitted with magnified optics.
- Revise the Handgusrd Takedown Bolt so that it is “Tool-Less”. See the HK Hanguard Takedown Bolt for inspiration, wherein they use a Bolt Locking Lug in a recess to turn the Takedown Bolt’s Head.
- Reduce the diameter of the Barrel Nut to make it HK 416/MR223-compatible, including the Lockinig Bolt groove so that the Mk3 will accept HK Handguards as an option.
EXAMPLE BUILD
Below is an example of a utility build based on the R18 Mk3. The list of additions is detailed below:
– EoTech VUDU 1-10x Low-Power Variable Optic in American Defense “Recon” QD Cantilever Mount
– RiteOn Miniature Red Dot Sight on Offset Mount
– Midwest Industries Iron Sight Set
– Streamlight TLR-HL White Weapon Light
– Magpul Vertical Foregrip
– Magpul MOE Pistol Grip
– Strike Industries Ambidextrous Magazine Release
– BCM QD Slot for Sling Swivel
– B5 Systems SOPMOD Buttstock
– Magpul Windowed 5/30 Magazine with Ranger Plate
CONCLUSION
The R18 Mk3 represents a significant leap forward for the design as well as the methods of manufacturing, assembling and inspecting the Sterling Arms International rifles prior to sale. The use of upgraded T7075 aluminum alloy, Stainless Steel for selected parts, and a Melonite-lined Chamber and Bore are all major advancements in the durability and longevity of the system, further enhancing the rifle’s value. With the latest enhancements and redesigns, the R18 Mk3 arguably represents not only the most advanced Canadian-manufactured Short-Stroke Piston rifle design currently on the market, but also the most cost-effective in terms of value for dollar. With the 33% reduction in MSRP from $2700 CAD to just $1800 CAD (initially), the Mk 3 also clearly provides the greatest value for the buyer’s precious dollar. My initial impressions based on handling the Mk3 and carefully examining the rifle’s component parts are highly favourable. Provided the new rifle delivers acceptable accuracy together with respectable reliability and reasonable durability, I believe that SAI has a serious contender with a winning combination of quality and affordable price on its hands. I predict a high degree of popularity for the R18 Mk3, as the principal competition for the Internal-Piston design of the Lockhart “Silver” Raven within the Canadian modern utility and sporting rifle market.
Part 2 – Shooting Impressions and Accuracy Results. Stay tuned for Part 2 of my Review once I get a chance to hit the range a few times for some accuracy and reliability testing. The Test Rifle that I have for the Part 1 Review cannot be fired due to a prototyping tolerance issue. That should be resolved within two weeks, with live-fire testing commencing shortly afterwards. Expect approximately 3 weeks (give or take) between Part 1 and Part 2 – Shooting Impressions and Accuracy Results.