Rear peep sight diameter

[bluedog]

Can someone give me the spec on the diameter of the M16A1 standard range peep, and also that of the stock long range peep on the 6921?

[kc7txm]

According to "The Black Rifle: M16 Retrospective" by Stevens and Ezell the M16A1-type flip sight has a 2mm and 5mm aperture (page 369). That looks to be about right on my A1 Colts.

I do not know about the aperture size on the Colt Model 6921.

[bluedog]

Have the size of the wings and post remained basically the same?

[kc7txm]

Thanks. Wow, 5 mm seems huge. Have the size of the wings and post remained basically the same?

Yeah, 5mm does seem large, I just pulled out an inside micrometer and the oldest and newest A1 Colts I have are 4.3 mm and 2 mm apertures.

I do believe the size of the the apertures remained the same until the A2 sight was released. "The Black Rifle: M16 Retrospective" by Stevens and Ezell doesn't mention anything about changing the sights (the book is a history of every change in the AR-15 from birth to 1986) until the A2 in 1982. It does mention that some people complained the 0-200 meter battle sight aperture was too small and the Long sight was not small enough. Ergo the changes on the A2 with different aperture sizes.

[bluedog]

Right, thanks again. Although I haven't fired with an A1 (0-200m) sight for a long time, my recollection was that it is smaller than the current design.

[coldblue]

Can someone give me the spec on the diameter of the M16A1 standard range peep, and also that of the stock long range peep on the 6921?

We (USMC/1980-1983) put the 5mm optional flip peep on the M16A2 in order to facilitate later unit installation of the Low Light Level (LLL) Army lumimous front sight post. (The front sight post being a component an Operator could install without the need for special tools, unlike needing an Armorer to change the rear peep out using a hammer. punch, etc.)
However, the LLL front post option was never followed up on my successors like it should have been, given the hours of darkness on any battlefield in a 24 hour day. This was primarily because of lack of advocacy; and that the control, accoutability, disposal, etc., of the glow in the dark LLL componet is a logistics nightmare in the military gave people an excuse to sit on their hands over the requirement.
By the way, 5mm was selected because that was the size of one leaf of the peep that came in the Army's LLL kit back in the 70's.
The original square front sight posts of the prototype A2's (M16A1E1) were wider than they are today because I took their measurement from an M14 as well as a host of other proven combat rifles and averaged them together. However, given the M16's shorter sight radious, they were said to appear too fat by some "belly shooters." So we took some advice from Fort Benning and narrowed it to approximate the width of an E silhouette at 250 meters.
Also by the way, I still have the fat ones on my carbines because I can acquire a good sight picture quicker in snap-shooting.