Excellent overview of Prime’s Colt upper, for those new to these gold standard CNC receiver sets – courtesy of Juicy at Overhoppers.


This arrived late last week – fully sick! Prime CNC’ed goodness…


Quick notes on fitment:

  • Systema charging handle fit.
  • Systema dust cover & pin fit, though upper corners of dust cover were a bit tight.
  • Systema black and silver cylinders fit a little tighter than in Systema upper, though not overly so.
  • Systema steel 14.5″ outer barrel fit, though the diameter of the chamber seemed slightly smaller than the hole in the receiver by a fraction of a MM – Systema upper fit slightly better.
  • Systema barrel nut was harder to install, some chasing of the threads was required to complete it.
  • Buffer tube cap on my lower requires reshimming after installation of Prime upper.
  • Minor play between Prime upper and Systema lower – about the same as the Systema upper I had before.

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