General Purpose Cartridge Saga Update -- Treading Water
Posted 2017-10-28 15:12 PDT | Tags: defense gpc ballistics
(Note: This wasn't going to be the next entry I would write, but it ended up being the one that got finished before the other.  Writing is hard!)
It's been five years since I last wrote about the General Purpose Cartridge:
To rehash, the GPC is a hypothetical military rifle cartridge suitable for replacing both, NATO's legacy 5.56x45mm assault rifle cartridge and its 7.62x51mm full-power rifle cartridge.
In order to accomplish this, the GPC would have to satisfy a variety of semi-contradictory criteria:
      * It must be as lightweight as 5.56x45mm (or nearly so), to avoid increasing the soldier's burden,
      * Its recoil must be sufficiently gentle that carbines firing it in automatic mode are controllable,
      * Its terminal ballistics must at least match that of 5.56x45mm at short range (lethality at 50m),
      * Its terminal ballistics must at least match that of 7.62x51mm at long range (lethality at 800m)
      * Its external ballistics must at least match that of 7.62x51mm at long range (flat trajectory, low wind drift).
These criteria made the GPC a thorny enough subject, but recent events have made writing about it even more difficult:
      * The US Army has moved the goalposts to an undisclosed location with the introduction of new "enhanced performance" cartridges -- the M855A1 for 5.56x45mm and M80A1 for 7.62x51mm,
      * The terminal ballistics of these new cartridges do not fit neatly in existing analytical models,
      * Since the Army has decided to go lead-free, should a GPC also be lead-free or should it incorporate lead for its ballistics-enhancing characteristics?
      * Since the UK MoD is moving towards nonfragmenting bullets (with inferior terminal effects), should a GPC also be restricted to nonfragmenting bullets?
      * The methods used in my previous two articles had flaws: the empty brass weights for some cartridges were underestimated, and the lethality model was too primitive,
      * The AMU has purportedly decided on the new "264 USA" as its GPC cartridge, of which very little is yet known.
      * The AMU has argued making changes to its small arms doctrine to accomodate the characteristics of the 264 USA.  These arguments are relevant to the GPC concept as a whole, and could be used to justify altering its criteria.
So, before I can write about the GPC again, I need to purchase samples of more cartidge types and measure them, and update my methods.  I need to learn more about the ballistics of M855A1 and M80A1, and of 264 USA.  I need to justify my reasons for using or not using lead, and using or not using fragmenting bullets.  I need to decide whether the AMU's arguments are sufficient to justify changing the criteria for the GPC (particularly its weight constraint).
I haven't given up on the subject, but these things take time.  In the meantime I will try writing about these various issues separately.