Skip to main content
Help Center Community Shop

AR15 receiver question

BUCKAWHO
At what point did the mounting holes in receivers change from small to large, or vice versa? How do I determine what I have? Just measure the pin? What are the different sizes? BT
0

Comments

3 comments

Date Votes
  • fordsix
    as far as i know colt is the only one i know that has non milspec holes and that was in the early 90's
    0
  • nononsense
    BUCKAWHO,

    From my notes and an unattributed source:

    quote:Small Hole vs. Big Hole
    Colt owners often refer to having a small or large hole upper receiver (and corresponding lower receiver). Small hole receivers of .250" are the "milspec", but during early production by Colt for the civilian market, they produced rifles utilizing a .315" spec, so as to preclude use of military uppers on civilian lowers. This production lasted until roughly 1993-1994. As a general rule of thumb all Colt "unblocked" lower receivers, are large hole, while pre-ban "blocked" lower receivers represent transition years where occasional variations popped up.

    Best.
    0
  • BUCKAWHO
    From this I gather that .250 holes and pins are the norm. And that this question is really not much of a problem for most owners. Thanks for the replies....BT
    0

Please sign in to leave a comment.

Recent Activity