Colt's began the process of seeking approval to produce a semi-automatic only variation of their AR-15 rifle for commercial sale by submitting a prototype semi-automatic only version, serial no. GX4968 (Gun Experimantal no. 4968) to the Treasury Department on October 23, 1963. A selective fire rifle was also provided for comparison purposes.
Colt listed the following nine changes which they had made to the semi-auto version to prevent the re-conversion to full auto fire:
1. Removal of the automatic sear.
2. Elimination of the automatic sear hole in the lower receiver.
3. Elimination of the automatic sear well in the lower receiver.
4. Removal of the automatic sear hook on the hammer.
5. Removal of the automatic sear trip notch from the bottom rear portion of the bolt carrier.
6. Modification of the selector to eliminate the automatic setting.
7. Elimination of the "AUTO" position identification marking on the lower receiver.
8. Mechanical restriction of selector lever movement to two positions only: SAFE and FIRE.
9. Enlargement of the front pivot pin holes in both upper and lower receivers, and use of a larger-diameter front pivot pin.
On October 25, 1963, the Treasury Department adivsed Colt that in addition to these nine changes, they wanted the upper and lower receiver pin lugs relocated, in order to further prevent the interchangeability between semi-auto-only and selective-fire receivers. This was done by moving the enlarged pivot pin holes in the upper and lower receivers down and rearward.
Permission was granted on December 10, 1963 for Colt to commence production of the semi-automatic only AR-15 embodying the above ten changes. On January 2, 1964 the initial "Original First Issue" Colt AR-15 Sporter rifles were released for sale.