Nucleus Gen2 Bolt Action

999.00 999.0 USD


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Made in the USA.



Must be shipped to a licensed FFL (Federal Firearms Licensee).  Your order confirmation email will contain FFL shipping instructions.
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Nucleus Gen2 Bolt Action

Odoo CMS - a big picture


Odoo - Sample 1 for three columns

Bolt Stop

Hardened stainless steel bolt stop.  Press the tab down to remove the bolt, release the tab and the spring returns the bolt stop to the locked position.  The bolt stop load bears against the slot in the receiver.

Odoo - Sample 2 for three columns


Claw-type extractor with controlled round feed.  Secure and large contact area grips the cartridge. 

Snaps right over the cartridge when single feeding.  There is no downside to controlled round feed.  

Odoo - Sample 3 for three columns


Inertial style ejector.  Simply pivots into position when activated by the bolt head lugs.  Extremely reliable.  

Odoo - Sample 1 for three columns

Bayonet Bolt Shroud

Remove the striker assembly with no tools.  Press in the bolt shroud locking pin and rotate a 1/4 turn or so.  To reinstall: slide in the assembly, compress the striker spring, and turn back to locked position.  

Odoo - Sample 2 for three columns

Bolt Knob

Lift with the side of your hand for a fast bolt cycle or grab the knob like a traditional handle. 

Odoo - Sample 3 for three columns

Interchangeable bolt head and extractor 

The bolt head and extractor are interchangeable to support multiple cartridges.  They can be swapped in about 1-2 minutes with no tools using the bayonet style bolt shroud.  The extractor is specific to each bolt face diameter for optimal engagement with the case.



Nucleus Bolt Action

  • Proudly engineered and manufactured in the USA

  • Short action weight 1.9 pounds (30 oz), long action weight 2.13 pounds (34 oz) 

  • 80 degree bolt rotation

  • Three toroidal locking lugs do not require lapping

  • Controlled-round feed extractor

  • Controllable Springfield inertial ejection

  • Exceptionally smooth

  • Corrosion resistant black nitride finish

  • Three anti-bind rails

  • Interchangeable bolt heads

  • Dual cocking cams

  • 100% cock on opening

  • Integral bolt handle

  • Ergonomic interchangeable bolt knobs

  • Keyed recoil lug, pinning not required

  • Pin-less interchangeable scope mounting rail is secured to the receiver by five conical-head, Torx-drive screws.

  • 062 inch diameter firing pin tip for small and large primers, adjustable firing pin protrusion

  • Savage small shank pre-fit compatible barrel thread

  • Compatible with Rem 700 triggers

  • Compatible with Rem 700 stocks and chassis

  • Rem 700 style mag well accepts AICS style mags, long action accepts CIP length mags (does not accept BDL bottom metal, Mausingfield does)

Parts & Accessories >>

Bolt Action Interface Drawing >>


Short/Long Action Bolt Stop

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Short Action

The Short Action has a tab style bolt stop similar to the Mausingfield but on the opposite side (the 3 lug bolt head necessitates a different design than the 2 lug Mausingfield).  The tab is pressed down to remove the bolt and a spring returns it to the locked position when the tab is released. 

We test our bolt stop designs by slamming the bolt into the bolt stop as hard as we can hundreds of times to ensure it will always stop the bolt.  During normal use no one typically slams the bolt open nearly that hard, but if you do the bolt won't come out.   

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Long Action

The Long Action has a rotational style bolt stop which is the same as the Archimedes.  The bolt stop is rotated with the bolt in the retracted position and remains open until rotated to the closed position.    




  • Complete action

  • 2 Trigger pins

  • Tools: washer to compress striker spring

Barrel interface: The barrel thread specification for Nucleus is 1.063 – 20 UN 2B making it compatible with many off-the-shelf barrels such as Savage small-shank pre-fits.  Conventionally threaded and shouldered barrels can also be used with the Nucleus.  The distance from the bolt face to the forward face of the recoil lug is 0.825 +/-0.001 inches.

Bolt:  The Nucleus uses a bolt that is machined from a single piece steel and subsequently heat treated for strength.  It has an integral handle making it practically impossible to break off.  An integral cylindrical shaft extends through the knob thus maximizing strength.  The bolt knob interface for the Nucleus is the same as that of the Mausingfield and unique to American Rifle Company.  

Bolt Head: (Patented and patent pending) The Nucleus uses an interchangeable bolt head featuring three Toroidal locking lugs, each having an anti-bind slot that engages three corresponding anti-bind rails machined into the receiver using a wire EDM.  The toroidal locking lugs bear against a spherical surface within the receiver thus obviating the need for lapping the bolt to the receiver.  Bolt heads are available for the 223 Remington, the 300 Win Mag, and everything in between including the 224 Valkyrie and the 6.5 Swede.

Bolt Knobs: The Nucleus is designed for use with American Rifle Company’s proprietary bolt knobs that are ergonomically designed for enhanced control of the bolt while cycling the action. 

Bolt Manipulation:  Cycling the Nucleus requires rotating the bolt by 72 degrees which is approximately the maximum possible without seriously compromising primary extraction.  Dual cocking cams are used to increase cocking efficiency thus minimizing the force required to cock the action.  The nucleus is 100% cock-on-opening.  When the bolt is open, the placement of the bolt knob positions the hand well clear of the scope for unobstructed rearward and forward movement.

Bolt Shroud:  The Nucleus uses a flanged bolt shroud like that of the Mauser 98 in that its flange obstructs the flow of rearward moving gases and particles resulting from over pressure events and case head separations. Additionally, a spring-loaded locking pin like those of the Mausingfield and Mauser 98 prevents accidental rotation of the shroud with respect to the bolt when open and retracted.  The locking pin obviates the need for detents at the aft end of the bolt which adversely affect the smoothness of the bolt cycle. 

The striker assembly of Nucleus G2.0 can now be removed by depressing the bolt shroud locking pin and then rotating the bolt shroud with respect to the bolt by one-quarter of a revolution, enabling  tool-less take-down of the bolt for cleaning and for bolt-head exchange.

Bolt Stop: Substantial in size, the bolt stop of the Nucleus is extremely rugged and dependable. It is not pinned to the receiver.  Instead, the bolt stop itself is a large pin that obstructs the 12 o’clock lug of the bolt head and transfers loads directly into the receiver.  It will prove to be among the most rugged bolt stops ever used in bolt action rifles, on par with those of the Mauser 98 and the 1903 Springfield.  Bolt removal is easy.  Simply retract the bolt, rotate the bolt stop by 180 degrees, and remove the bolt.  The bolt stop can only be rotated when the bolt is fully retracted thus preventing accidental removal.  The center of mass of the bolt is located to prevent rotation under the high accelerations of recoil.  Lastly, the forces associated with the bolt striking the bolt stop drive the bolt stop into engagement with the receiver.

Ejector: The Nucleus uses an ejector that is very similar to that used in the Model 1903 Springfield—a compact, hardened-steel ejector freely pivoting on a high-strength steel pin. It is located at the aft end of the receiver, well away from the breech where the blast resulting from an overpressure event or a case head failure would be most intense. The momentum of the rearward-moving bolt forces the ejector to pivot into engagement with the case head through a slot in the bolt face. The Springfield ejector also enables the shooter to control the intensity of the ejection process. It is the same ejector used in our Mausingfield bolt action and we encourage you to learn more about the ejector by clicking here.

Extractor: (Patent Pending) The Nucleus uses a claw type extractor which offers controlled-round feeding functionality while cooperating with the three-lug bolt design.  It is well suited for cartridges ranging in size from the short 6mm Dasher all the way up to long magnums.  Conceptually, its design is like that the famous Mauser 98 claw extractor in that it can engage the case head without the use additional springs or plungers.  Instead, a compliant tail provides the spring force necessary for engaging the case head.  The extractor is trapped between the bolt head and the bolt obviating the need for small pins.  During extraction, the extractor slides forward to engage an undercut in the bolt head thus preventing accidental disengagement of the case head.  The extractor of the Nucleus is an excellent example of an American Rifle Company comprehensive and highly engineered solution.

Magazine Compatibility: The Nucleus is compatible with American Rifle Company’s ARC mag, the Accuracy International CS mags (AI CS), Accurate mags like those from Accuracy International, and Alpha mags.  It is not compatible with the Accuracy International’s AW mag.

Metallurgy: The Nucleus is made from high strength alloy steel.  It is not made from stainless steel.  The Nucleus undergoes a salt bath nitride finishing process to harden and blacken its surfaces.  The resulting finish effectively resists corrosion and reduces friction thus enhancing the smoothness of the action.

Recoil Lug: (Patent Pending) The Nucleus has an innovative recoil lug that does not require pinning to maintain proper orientation with respect to the receiver during barrel installation.  Instead, proper orientation is easily maintained by a tab which extends upwards from the top of the recoil lug and engages a slot cut into the bottom of scope mounting rail.  The recoil lug is made from hardened steel and has a corrosion resistant, black nitride finish.  Its thickness is 0.185 +/-0.0001 inches.

Scope Mounting Rail: Made from 7075 aluminum alloy, the rail has a black, hard-coat anodized finish.  It is attached to the receiver using five high strength, 410 stainless steel, 8-36 screws.  The overall length of the screws is 0.375 inches.  The rail that has a tapered slot that engages a similarly tapered key machined into the top of the receiver, just like those of the Archimedes.  So, in addition to the five conical head screws, the key provides an additional constraint for maintaining alignment between the rail and the receiver and for resisting the forces imparted on the rail by the recoil lug during barrel installation.  This solution ensures reliability, scope mounting choices, and economy. 

Stock and Chassis Interface:The Nucleus is generally compatible with stocks and chassis designed for use with the Remington 700 and its clones.  The bolt stop of the Nucleus is located near the top of the receiver and is therefore well clear of all stocks and chassis except for tubular chassis such as the Eliseo.

Striker Assembly: (Patent Pending) The Nucleus uses a dual cocking cam striker assembly for enhanced cocking efficiency thus reducing the effort required to cock the action.  The 0.062 inch diameter striker (firing pin) tip reduces the likelihood of piercing small rifle primers.  Adjustable tip protrusion from the bolt face is made possible by an interlocking nut and washer that also serves as the abutment for the striker spring.  The striker is connected to the cocking piece by a thread.  Complete passage of the striker through the cocking piece is prevented by a head at the aft end of the striker.  Additionally, disassembly of the bolt assembly is facilitated by a threaded hole in the aft end of the striker into which a screw may be inserted to hold the striker in the rearward position against the main spring force. When the screw is in place, the striker assembly can easily be unscrewed and removed for the bolt assembly.

Trigger Interface: The Nucleus is compatible with aftermarket triggers designed for the Remington 700 and its clones.  If possible, triggers should be purchased without the bolt stop releases.  The Nucleus does not use a trigger hanger.

Gen2 Updates

Nucleus® Gen 2.0

We decided to update the Nucleus for two reasons.  First, and perhaps most importantly, is reducing the elapsed time between order placement and fulfillment. To that end, an effort to improve production throughput was made by reducing the number of unique parts that we must manufacture. For example, the entire striker assembly of Nucleus G2.0 is now identical to that of the Mausingfield while its bolt head and the extractor are now identical to those of the Archimedes.  And secondly, we want to give you more of what you want so Nucleus G2.0 has been updated with the following:

Keyed rail interface

For scope mounting, Nucleus G2.0 uses a Picatinny rail that now has a tapered slot that engages a similarly tapered key machined into the top of the receiver, just like those of the Archimedes.  So, in addition to the five conical head screws that were used on the original Nucleus, the key provides an additional constraint for maintaining alignment between the rail and the receiver and for resisting the forces imparted on the rail by the recoil lug during barrel installation.

Bayonet style bolt shroud

The striker assembly of Nucleus G2.0 can now be removed by depressing the bolt shroud locking pin and then rotating the bolt shroud with respect to the bolt by one-quarter of a revolution, enabling  tool-less take-down of the bolt for cleaning and for bolt-head exchange.

80 degrees of bolt rotation 

In order to improve the smoothness of the bolt cycle, maintain an appropriate level of cocking effort, and still provide adequate clearance between the shooter’s hand and the scope during bolt cycling, Nucleus G2.0 has 80 degrees of bolt rotation.  The original Nucleus had 72 degrees.

Smoother cocking and closing

Nucleus G2.0 slightly over-cocks when lifting the bolt handle and then de-cocks by a tiny bit when closing the bolt, thus no cock-on-close will be the standard offering.  Moreover, the cocking piece never falls into the cocking cams when closing the bolt thus eliminating any bump-on-close that would otherwise result from a slight amount of re-cocking.  The cocking behavior of Nucleus G2.0 is now essentially identical to that of our current Mausingfield action.

Optional cocking pieces

To accommodate variations among triggers that will be used within Nucleus G2.0, we now have an inventory of cocking pieces varying by 0.25mm (0.010 inches).  Additionally, those wishing to enable their action to cock-on-close can do so by ordering a cocking piece that will provide that functionality.  Cock-on-close cocking pieces can also be modified by a competent gunsmith in order to eliminate any de-cocking and cocking-on-close.

The smartest bolt knob in the industry

Nucleus G2.0 comes standard with our short barbell knob which we believe is the smartest and most ergonomic bolt knob available.  The knob boasts a function driven design that makes high-speed cycling of the bolt as easy as possible.

Improved fully-retracted bolt guidance

The receiver of Nucleus G2.0 cradles more of the bolt body than did its predecessor, thus making it a bit easier to avoid binding while cycling a bolt that was already easy to cycle.  An incremental improvement at best, is was essentially free to implement and therefore we included it.