MAMBA Case Neck Expander



  • Often, whilst seating several bullets, we experience a distinct variance in the resistance to seating between these bullets.  Some bullets need much more seating force than others.  The most likely reason for this variance, is inconsistent inside case neck dimensions/diameters;
  • Consider the following:  If cases have inconsistent neck wall thickness, and they are sized to have the exact same outside diameter, surely the diameter on the inside of the case necks would follow suit, and could not be consistent;
  • Remember, the bullet sits inside the case neck, not outside.  Consistency is everything in shooting and equates to consistent and accurate results;
  • If you currently experience any variance in the force needed to seat bullets: Does the present use of normal expander buttons and case neck turning really deliver the required results for consistent case neck tension?  Probably not;
  • Many reloaders, including myself, experience very positive results from employing Case Neck Expander Mandrels for achieving consistent case neck tension.  Our results indicate a significant reduction in the standard deviation (SD) and extreme spread (ES) of our measured muzzle velocities;
  • Fit the Expander Mandrel through the bottom end of the Expander Die/Body & use the supplied bolt and washer to tighten it by hand only;
  • The screw on the bottom of the Expander Mandrel bottoms inside the case against its web.  The screw is already factory-set to function for all cases specific to the particular bullet calibre Mandrel.  The Expander Die & Mandrel is therefore self-regulating and needs no adjustment or setup;
  • Screw the assembled Expander Die onto the press until enough thread is engaged = screwed in at least 3 turns;
  • Loosen the Mandrel bolt ¼ of a turn to achieve a rattle fit in the Die/Body + the Expander Die has no locknut.  Together this achieves a floating and self-centring Expander Mandrel;
  • After cartridge cases are fully prepped and sized, lubricate the inside of these case necks thoroughly;
  • Place a case in the shell holder and carefully lower the press handle to push the expander mandrel into the case neck.  Work the expander mandrel up and down inside the case for around 3 repetitions, taking care not to hit the set screw too hard against the inside of the case head.

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