American Rifle Co : Nucleus Gen 2 Short Action, RH - .308

American Rifle Co. : M9B1-TSR-00645
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The Nucleus Gen 2 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" - American Rifle Company    



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.



  • 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)
  • Length: Short [2.94" mag length]
  • Hand: Right
  • Bolt Face: 0.473" [i.e. 308 Win]
  • Action Rail: 20 MOA [5.8 mrad]








FFL Requirements & Magazine Restrictions

This item has to ship to an FFL. Please read the attached information. Shipping Rules & Magazine Restrictions.