You asked: "...What about the heavy profile in front of the fsb?
I was under the impression that the reasons for adding the extra meat at the front was in error...."

Not in regards to preventing the barrel bending during dynamic bayonet fighting drills or banging against rappelling towers, etc.
The Operational and Engineering testing proved the heavier profile in front of just behind the FSP was many times more resistant to being ben in our more aggressive training environments than those of the other services..


Now it is also a fact (now, established many years after this testing) that a burr on the gas port can act as a "scraper" of sorts and may cause a build-up of bullet jacket material that will cause the military's "barrel straightness gauge" to get hung-up in that general area.  A bore brush and an electric drill can usually fix this.

However, I noted more recently, that the copy of the Army 23&P TM on the internet directs Armorers to "re-bend" bent barrels over a bench so the drop gauge passes through.  So maybe we have at least two potential issues with the drop gauge, "bent barrels", etc.

The main advantage was the ability, that is if they cared to train for it, to accurately engage targets at greater ranges than they could before.
That was why we went with the 800/300 rear sight.  Rifle fire at such ranges is directed by small unit leaders with a fire command to a group of firers, such as:
"Squad!
Rifleman only,
Direct front.
Abandoned house with enemy squad.
Range 550 meters.
Adjust sights.
On my command...Fire.

This is how a small unit could accurately lay down a base of fire while a second element conducted an envelopment.
My experience in Viet-Nam as an Infantry Platoon Leader was that we always needed to lug around M60 machine guns for such purposes, as our organic M16A1's lacked a  longer than battle sight capability.  I mean without the M60, we could get pinned down in the rice paddy area I worked in by a couple of SKS's from a tree line only 400 meters out.  I wanted the M14's/M1's range adjustable sight capability back!

I bent over backwards on design improvements/changes to keep the Infantry School at Fort Benning at the M16A2 table.  One example was maintaining a simple method for obtaining their 25 meter zero, which by the way the Marines were using then as well.  That required one click of A2 rear sight elevation past the 300 meter mark; which allowed you to shoot "point of aim = point of impact" at 25 meters for your zero.  Then rotate one click down to the 300 when finished.  The POA=POI was much easier for everyone to understand versus the off-set impact method of the A1.
The previously mentioned Army report kind of deliberately ignores this accommodation in their criticism, as well as pointing out the A2's lack of 25 meter zero symbol (like a triangle) on the range adjustment wheel.  Back then in my mind, as well as several at Ft. Benning at the time, that if a Soldier could remember what the little triangle was used for, then he/she could remember the one click up as easily.  This was well covered in the TM's I revised as well as the 25 meter zeroing target I developed.
And like I said above, we did not change the tread pitch of the front sight post so an A1 post could be used, as well as their Low Light Level sight kit.  And using an A1 front sight post maintained total interoperability with their existing targets and their zeroing targets metric grid adjustment values.

The much bigger issue was them switching from their well established 250 meter zero to our 300.  But how I did that is another story...

One thing I forgot to mention, re: the 5/8" buttstock length increase, was that HEL's input was based on how far "ideally" behind the rear sight peep your eye should be for the 95th percentile Soldier.
And as with all the changes, although many were subjective on my part, I had to present objective data on the improvement level, or equal to data, to not only my reporting senior at Quantico, but a board of senior officers at Headquarters Marine Corps on a periodic basis during that three year period when I was assigned to the project at Picatinny.

Here you go:

BZO Zero Change (1980-1983)

At the time in 1980, Army rifle Battle Sight Zero (BZO) doctrine was 250 meters whereas the Marine Corps was 300 meters (well, 300 meters sort of).  Sort of, because there was only one metric rifle re-qualification range in the Corps at the time at Camp Pendleton.  All other such ranges were decades old and in yards, but at the end of re-qual week, we pretended they were meters for the final BZO adjustment.

Marines determined BZO at the end of annual rifle re-qualification.  Marine Corps re-qualification at the time fired 50 rounds across the course of fire starting at 200 and ending at 500.  All hits were “disked” by personnel in the butts, one or ten shots at a time, so the Marine could make subsequent sight adjustments between shots in slow fire if necessary.  These hits were also recorded by the shooter in his Shooter’s Log Book.  Sight adjustments at each range and sometimes even firing positions were reset accordingly (aka: dope changes) and were also recorded from day to day in a Shooter’s Log Book as well.  The 200 was “slow-fired” from two positions:  standing and kneeling.  The 300 was fired sitting and then 10 rounds prone rapid fire.  The 500 was 10 rounds of slow fire from the prone.  The targets were as follows:
200: small bull’s-eye.
300: small bull’s-eye (sitting) and a “head & shoulders” silhouette (prone).
500: E-type silhouette.
At the end of qualification day at the 500 firing line, coaches supervised the rifle sights being re-set to the Marine’s 300 prone rapid fire dope and then adding one click for the metric element.  That was our battle sight zero position.  Previously, the same basic zero set procedure for 300 had been applied to the M14 and M1 rifle sights—less the metric click.

As far as I know and/or observed, Army requalification with the M16A1 was fired from a fixed, fox hole supported position at E- silhouette targets from close in to out to 250 meters.  The targets were hit sensitive.  Sights were not adjusted during the course of fire (as they were during Marine requalification).  This course was fired after an Army 25 meter zero, 25 meters being 1/10” the 250 meters battle sight zero range; so one centimeter worth of clicks at 25 would equate to 4 cm at 100, 8 cm at 200, and 10 cm at 250.  That is to say, 250 being divisible by 25 x 10, or whatever the logic was…

This 1/10 metric math, I suppose, was to make dope changes easier for the Soldier to understand, even though on the qualification course, sights were not adjusted and the actual target hits were not “disked,” so the Soldier only knew he had hit a target, not if the hit was high, low, whatever.

So the first thing Ft. Benning (The Infantry School) did not like about the Product Improved (PIP) rifle’s adjustable rear sight was the lack of a clearly marked 250 meter zero mark on the range wheel.  What I came prepared to do, however, was to show how the new SS109/M855 rounds’ flatter trajectory achieved an increase in BZO range effectiveness without the need for any changes in their training, re-qual and zeroing ranges, or doctrine.  My Point of Contac (POC) in those days with the Infantry School was a Mr. Jack Pritchard, who passed away several years’ later, God rest his soul.

Jack understood my first briefing on the flatter trajectory issue and impact on zeroing which illustrated the 193 vs M855 trajectories on a two-dimensional briefing slide as you might well imagine.  But Jack was reluctant to run such a potentially controversial issue up the flag pole, with conventional presentation slides (in those days before power point, using overhead projectors onto a screen, etc.).  He said he needed a more graphic, hands-on exhibit that “…even a General could understand…”

I put some thought into how to do this, and scheduled range time at the Army’s NATO Test Range at Fort Dix, New Jersey the following week.  Part of this range complex was a flat 1000 meter outdoor range with surveyed-in range markers in meters, etc.  What we did was to use a wheeled hand cart to mount a “back to back” pair of E-Silhouette targets, which were the same size as the Army qualified on, so I knew they would recognize and identify with them later.  We then moved the cart and a new target pair the required distances from my fixed firing position.  The “back to back” target idea was to create a “xerox” copy of each 10-round shot group at each range fired.  That way both Jack and I were briefing from the same data points, using virtually the same targets.

The Colt test rifle (designated as M16A1E1 for this project) had a 1:7 twist barrel, adjustable rear sight (i.e., the very early version with the range reading peep hole at the rear of the carrying handle) along with some of the (thank God!) Belgian SS109 ammo that had been so kindly provided by the Canadian Army a few weeks earlier.  (Note: this was before the case deflector was added to the upper receiver which leads to yet another chapter in this saga).

After I zeroed using the new procedures I had developed and my prototype 25 meter zeroing target at 25 meters, shooting “point of aim = point of impact” we mounted a new pair of E-silhouettes and moved them to the 100 meter line.  I then fired 10-rounds, slow fire from a supported prone position, aiming center of mass on the E-silhouette.  The center of mass of these E-silhouettes was indicated by covering the lower half of the E-silhouette with a sheet of white paper (as illustrated in the graphic below).  After I fired the 10-rounds, we moved to the target, replaced the E-silhouettes and moved to the next range.
The results are illustrated to the best of my memory below:


Jack was very happy with my “xerox” results, which he used effectively in subsequent Infantry School briefings, illustrating that the Army was not giving anything up by changing from a 250 meter zero, but in fact were gaining “yardage” due to the new NATO round‘s flatter trajectory; and having potentially increased effective range over the M16A1, considering the A2 rear sight’s range adjustment and loading longer, heavier bullets tailored for the quicker twist barrels.  I mean, I thank my lucky stars and the sage advice from ammunition engineers at Picatinny, namely Mr. Denis Conway, who counseled me that the 1:7 twist versus a 1:9, which was being favored by some at the time, would provide greater growth potential later for improved ammunition, i.e., the Mk 262, if it were needed due to changing battlefield conditions.

And let me state ahead of interested reader comments to this posting, I am remembering this from over 30 years ago.  So on the Marine Corps/Army requalification procedures, for example, I may have a detail a bit off here and there, but I think my comparisons (which are the point of the paragraphs in the first place) are right on, as well as germane to the discussion topic.  The shot group and trajectory impact group placements in the illustration are as accurate as I can recall, and I apologize in advance for any differences that subsequent shooting, and of the “Americanization” of the original Belgian SS109 round, may have illustrated differently.  All I can say is that in those days before my eyesight went a little south, I was very proficient in my iron sight/M16 shooting skill level.  I am also 100% sure that on that firing day, my 25 meter zero was dead center; the 300 meter target had five rounds above and five rounds below the aiming point (which was actually the major point of the exercise); and that all ten rounds at 350 were at or below the aiming point, but on the E-Silhouette target non-the-less (which proved to be the “frosting on the cake” for the Infantry School).

here is the graphic from the above discussion:

http://i1357.photobucket.com/albums/q759/D_A_Lutz/th_BZOsilhouettex4_zps0428b6c1.jpg

A link to this thread is now available in the FAQ Resource, and it is set to never archive.

Here is my response to the next question:

You asked:
“…Dave, that is great information!  It is too bad that the A2 rear sight didn't incorporate steel for the elevation wheel and windage wheel as well.  That would really help to make the rear sight assembly much more durable.  

That, along with the fact that the windage knob didn't have numbers on it to correspond with the hash marks (for quick zero check / confirmation) are the only main problems I have with the A2 rear sight.

Do you think the 0 - 200 meter aperture is too large?  Do you like how it is not same plane?  

Can you, or I, re post this info to that AR15.com thread for the awareness of all in the community?

The aluminum elevation wheel assembly and windage knob have actually held up well in service since 1983 when they were finalized.  And the aluminum helped keep both the cost and weight of the sight change down, as the Marine Corps was not interested in a more expensive or heavier M16 Service Rifle, just a better one.

Of course in short order as Military Rifle teams, target shooters and competitors saw the bull’s eye potential of the new rear sight and ammunition improvements and the M16A2, being the new Service Rifle, started making a domineering presence at the Camp Perry National Matches.  Hand in glove with this process were entrepreneurs manufacturing internal M16A2 rear sight parts (as you suggest) from steel to tighter tolerances and half-minute elevation clicks.  (By the way, it was no accident that such a conversion process was easy enough to do with simple hand tools, and by anyone with a little mechanical talent, i.e., a shooter did not have to rely on a Match Team Armorer to make the rear sight “better,” as I saw this happening down the road.)  The windage knob was always in half-minute clicks and did not need a finer adjustment.

Windage numbers.  Actually I filed “roman numerals” on another chamfered windage knob for just such zero check reference purposes.  However, in discussions with Colt’s engineer Mr. Harold Waterman, numbering the ten windage half-minute clicks 0 through 9 would only work well for left windage adjustments as the first “click” left indicating at 12 o’clock would be the “1.”  Whereas the first click of right windage would indicate “9.”  So we kept the marking “neutral,” we went with 10 hash marks around the chamfer.  What most Marines are taught for zero windage position is to use paint to mark the windage knob a corresponding reference point painted on the base.

On the 0-2 aperture, that had several consideration points and applications. First and foremost was its 5mm diameter “ghost ring,” was like those on some dangerous game rifles I had hunted with.  This type rear sight aids in addressing close range moving targets in close cover, versus a small diameter peep better used for more distant targets.  The 5mm was also the same diameter as the Army’s Low Light Level (LLL) sight system kit’s M16A1 replacement rear aperture.  However, that kit’s rear peep required an armorer to install, and then if the rifle was surveyed, be replaced with an original peep.  Consequently, few Soldiers (or Marines) ever gained the advantage of the kit included luminous front sight post.  I was keen on adding this night time aiming aspect down to the User level of maintenance, i.e., only requiring a front sight post change, considering my Viet-Nam experience, especially considering near half of a combat day is in the dark.  I remember one of my men in the Nam using dental floss stretched between his rear peep and front sight post as we prepared our gear for night ambush patrols.  I was never sure how well this worked for the Corporal, but at a minimum he was mentally preparing himself to actually aim his rifle at night (something that was rare in those days).

When the 0-2 aperture is flipped into firing position, it lowers the sight line accordingly for a more point of aim = point of impact (POA=POI) at closer ranges, i.e., 200 meters.   And as you know, this also equates to the popular 50 meter zero which allows the round’s trajectory to deliver POA=POI across these more common combat engagement ranges.  One just needs to train with the 5mm aperture and gain confident in your shooting ability with it.  I also saw the writing on the wall that smaller peep inserts could easily be made to “snap in” the 5mm for those more comfortable with a smaller peep at close range.  That was another element of “growth potential” I wanted built into the new Service Rifle.

 

M16A1 Buttstock Option

I guess I am still mystified as to why at least one of the Services did not request that the Army stock an M16A1 length buttstock assembly, molded from the new, stronger Du Pont Zytel material, as an option to the added length of the A2’s.  As we discussed with Colt and Engineers from Picatinny Arsenal the most cost effective way to increase the buttstock length, several options were developed and considered.  The one I selected was that most easily re-converted to the original M16’s length of pull.

By that I mean retaining the original M16A1 receiver extension (buffer tube) length was the key to this option and the major reason it was selected.  The buffer tube, being also the most expensive component of the buttstock assembly would have measurably increased the lengthening cost, and also significantly detracted from Armorers changing it back once the rifle was in service.  Whereas maintaining the standard buffer tube length allowed the buttstock to be replaced quite easily with a screw driver and a shorter length vented M16A1 buttstock screw.  

There were really only two new parts needed for the A2 buttstock change, those being a longer length vented buttock screw,
M16A1 Vented Buttstock Screw (overall): .565”
M16A2 Vented Buttstock Screw (overall): 1.136”
and a 5/8” thick spacer to fit between the rear of the buffer tube and the buttstock’s buttplate.

If one later installed an M16A1 buttstock, there two parts were set aside.  It was my plan once the decision was made that the optional A1 buttstock assembly be packed in the Supply System with the correct, shorter length (.565”) buttstock screw; unfortunately this action was never completed by my successors after I left the program at the end of 1983.

Actually, one other buttstock assembly part was changed as well.  This was the lower buttstock screw that secured the lower sling swivel to the assembly.  This was required because of the way the new polymer material “flowed” into the molding cavity.  So to get the best strength out of the molded part, the sling swivel needed to be relocated closer to the buttplate and this required a shorter screw.
M16A1 Lower Buttstock Screw Length (under the head): 1.20”
M16A2 Lower Buttstock Screw Length (under the head): 1.88”

Of course the buttplate assembly for the A2 stock was changed as well, but that is another story.

All my AR's carry a Santos 200 meter zero at this time, including my A2's.  Back then, I was changing so many things, to include "doctrine" I felt that changing the well established BZO any more than I was doing already inadvertently would be counter-productive.  I mean like most of the Army's 25 meter zeroing ranges were literally "in concrete."
I know that initially I wanted the Rifle Ranges to teach the large diameter rear aperture for the 200 yard/meter portions of annual requalification.  But what I observed were coaches insisting on shooters using the smaller diameter rear set at the “300 ”and making front sight height adjustments between and at the 200 and 300 to help raise a shooter’s numerical score (so they thought, by using the more precise smaller aperture.  This was anathema to me as the A2’s rear was specifically designed and intended to end the need for shooter’s to do this during requalification, rendering a complete safe weapon to allow the front sight post to be adjusted, etc.  So I went back to the rear sight mechanism and determined that one could “slip the scale” down three rear sight clicks below the 300 mark, and then retighten the set screw, which gave you a 200 meter setting with the rear sight all the way down and then up one click so it was not bottomed-out.   I wrote this procedure up and tried to get this change out to the Fleet.  That is how my A2’s are set up, and they still are adjustable "up" to 800.

I don't know the epoxy that Colt used, but I do remember it was light colored.  And only one was knocked loose during operational testing, so the epoxy was pretty good (for those days)!

the 1:9 option was a popular option at the final decision point on twist.  But a wise ammo engineer at Picatinny, Mr. Dennis Conway, suggested to me that although the 1:9 would be ok, the 1:7 would build-in "growth potential" for future ammo improvements.  I went with the growth potential and very glad I did. He was right "5 by 5," but it took a while for the Mk262 to make its mark, and of course it does need the quicker twist...but of course, that's another story