Colt AR-15 receiver pivot pin diameters vs application
The early SP-1 commercial AR-15, 1961-1966, utilize the .250" diameter receiver pin. SP-1’s from 1966 through the early production A2 Sporters, 1995-96, employ the .315" diameter pin. Post Ban A2 Sporters use the .250" pin. Also, the majority of aftermarket AR-15 clones from other manufacturers use the .250" diameter pin.
Colt AR-15 Extractor Spring Insert (Extractor Buffer).
The bolt assemblies for the .223 caliber AR-15 rifle and the 16" barrel carbine are identical except for the extractor spring insert. The insert is considered an integral part of the extractor spring assembly.
There is an easy way to tell the difference between the two inserts. The insert for the 20" barrel is blue in color; the insert for carbine is black in color. The insert for the carbine is made of an elastic material to assist in eliminating extractor bounce, due to its application on the selective fire N4 carbine.
Extractor spring assemblies for the carbine can be substituted in the rifle without impeding correct function. The rifle extractor spring assembly should not be used in a carbine, particularly a selective fire version, as a failure to extract could be encountered.
Colt two different sized pins for the hammer and trigger
Colt lists two .170" diameter hammer/trigger pins for the AR-15. The SP63158 #160-305-101 is the standard pin with a nominal diameter of .169-.170".
The SP64225 is an oversize pin with a nominal diameter of .171-.1713". This pin is used with the Accurized HBAR, CR6724 (introduced 1997). Due to the heat treating process, this pin may have a mottled, silver & blue finish.
Colt AR-15 firing pin types
There are three firing pin configurations utilized on the Colt AR-15. The configuration used by a particular AR-15 will be determined by the vintage of the firearm or the caliber.
SP62805, Brownells #160-304-003 is the designated number for the 9mm blow back breechblock.
SP62294 Large Flange (NATO stock # 1005-00-0017-9547), Brownells #160-304-002 . This firing pin has a nominal flange diameter of .375" and is typically used with a shrouded bolt carrier. This firing pin is typically found on M16 selective fire variants.
The very early SP-1 series commercial sporter AR-15 manufactured until the 1966/1968 period utilized, according to Colt sources, a large diameter flange that is unique to itself (larger flange then 62294) . We do not have a source for this firing pin configuration at this time. The period 1966 through 1968 was a transitional period during which Colt did a running production change to incorporate the small flange firing pin and altered bolt carrier into the commercial AR-15 variations.
Please Note: The circa 1995 Colt Parts Book shows the SP62294 large flange firing pin as being used in all but two applications. This is in error. With exception of the early SP-1 sporter and the M16 variants as noted above, typical post 1966/68 sporters will utilize the SP63039 Small Flange firing pin.
SP63039 Small Flange, Brownell #160-000-205 . Flange diameter is nominal .343". This firing pin is used in conjunction with a unique bolt carrier and hammer. The bolt carrier features a shallow ramp cut at the rear of the hammer path and no shroud at the rear of the hole for the firing pin. The hammer has a notch on the upper front striking face. The design concept behind these parts was to create a system that would prevent the firearm from going full auto should the disconnector fail or be inadvertently forgotten during reassembly of a firearm. In such an instance the hammer will follow the ramp cut down the rear of the carrier. At this point, as the bolt carrier moves forward to strip a fresh cartridge from the magazine, the notch on the face of hammer will engage the flange of the firing pin and stop the forward movement of the bolt carrier.
At the time this is written (3/1/01) it is the intention of the Colt Engineering Department to phase in, some time in the next two years, the use of the large flange 62294 firing pin with an appropriate bolt carrier for all commercial AR-15 production. It is felt that the original intent of the SP63039 small flange firing pin and carrier is easily circumvented and the parts no longer serve a purpose sufficient to justify the additional production costs involved.