BB57, I have to question your posts. I want to know the source.
1. Milspec ammuntion has never been close to 1 MOA. M16A1 ammo, M193 Ball was like 4.5 MOA and rejected @ 7.2 MOA. Springfield 30-06 and M1 Garand ammuntion was similar but not exactly that.
The acceptance criteria for M193 was a 2” mean radius at 200 yards. To get this they shot nine 10 shot groups for a total of 90 rounds.
For each 10 shot group they determined the central point of impact and then measured the distance of each hole from this center point. They then added up the total distance and divided by 10 to get the mean radius for the group. They’d do that for each of the 9 groups and if the average mean radius was 2.0” or less they would accept the ammunition lot.
Assuming the 10 shot groups were roughly circular (and they usually are), an average mean radius of about 2” equates to an average extreme spread of about 4”, and this is at 200 yards. 1 MOA is 2.094” at 200 yards and 4” is 1.91 MOA. That’s the *maximum* average for the nine 10 shot groups.
Since the vast majority of lots successfully met the standard and were accepted, most lots did better. Based on the relationship between a sample of nine 10 shot groups to the entire population where the ES of the population figure is 1.3 times the sample’s ES, statistically speaking the average for M193 lots tested would be about 1.46 MOA.
Now…that’s a 10 shot group fired out of a reasonably new test barrel at 200 yards. Performance out of an M16A1 barrel that had been in service for several thousand rounds would not be as good, but the fault would lie with the rifles and various degrees of bore erosion, not the ammunition.
This study on bore erosion on the M16A1 from 1975-77 is interesting. 27 rifles were tested with new barrels from 3 manufacturers using M193 and M196 at 20 rpm, 50, rpm and 100 rpm firing schedules. Rifles 1, 2, 3, 10, 11, 12, 19, 20 and 21 were the 20 rpm rifles and generally (with some variation and exceptions) showed an extreme spread of 4”-5” out to around 8000-10,000 rounds. The accuracy of the 60 rpm schedule rifles fell off quicker and the average of the 100 rpm schedule fell off quicker still. In short, higher rates of fire accelerates bore erosion and full auto wears them out quite quickly.
So…your observation is correct that the average M16A1 with several thousands rounds through it would no longer meet the original accuracy standard, especially if it had seen a significant percentage of full auto fire.
Interestingly, the focus of this study was on both bore erosion and accuracy, and also on the use of bore erosion gauges to determine when to replace them, using 7” and 9” extreme spread standards.
https://apps.dtic.mil/sti/pdfs/ADA037533.pdf
In my experience, as stated above, my Colt made SP1 and M16A1 uppers we’re department surplussed and were very low round count rifles, used to qualify once a year for a short number of years. Both of the rifles demonstrate 5 shot 1.5 MOA average groups with M193. A 5 shot group is much less challenging than a 10 shot group, but it’s also a group size well suited to the lightweight barrel in the M16A1 and early SP1.
In short, I’ll stand on my accuracy statement in terms of what the M16A1 and M193 were capable of when a comparatively new (less than 4000 rounds) barrel was being used.
2. I am thinking M16A1 sights are much coarser than 1 MOA per click. I don't know what it is but highly doubt 1 MOA. The old round post 5 click version is what we used early on and then switched to the Tritium posts which were coarser yet. Same thread pitch put had to go two clicks at a time to keep the Tritium visible.
My numbers for the sight adjustment on the A1 and A2 came from chapter 2 of FM 3-22.9.
3. I carried an M16A1 all but about a month of my career in the US Army Infantry (actually Paratrooper). I had Colt's, H&R's, GM's and at least 2 XM16E1's in my travels. I was a Drill Sergeant @ Ft Benning, GA. Army Doctrine is 250meter battlesight zero, accomplished by aiming at a Canadian Bull target @ 25 meters and impacting a bit below the point of aim. 50 years is a bit long for me to remember specifics. We never Qualified beyond 300 meters and fired the entire course of fire with the Short Range aperture. We only used the Long Range aperture on our rare trips to the KD Range. I was issued and Zeroed an M16A2 about a month before I retired. I never did get a chance to Qualify with one, but did shoot AR15A2 variants in NRA Highpower 20-30 years ago.
My 250m zero data above is based on the US Army practice of doing the 25m zero using the L aperture per chapter 5 of FM 3-22.9.
If you use the unmarked short range aperture it’s a 42m zero and would be impacting about -.8” low at 25m. That’s not inconsistent with what you’re saying, if you were zeroing with the short range aperture.
I distinctly recall shooting 350m targets with the M16A1 on US Army train fire ranges as I was impressed with the A1’s ability to hit them consistently at that range. I double checked my memory against FM 23-71 and the courses of fire include 350m targets.
I was raised in a family with WWII, post WWII and post Korean War military members and was extremely biased against the M16A1, partly due to .30-06/Garand and 7.62x51/M14 bias, and partLy due to the reports of poor performance and accuracy in Vietnam. Once I was issued a decent M16A1, I was impressed with its practical accuracy and those 350m targets were a big part of that.
I also found it to be reliable enough - provided I pulled the bolt carrier out and wiped it and the upper receiver down every time I had a minute to spare and after any low crawling through sand, dirt, leaf litter, field stripped cigarette butts, etc.
4. While a Drill Sergeant @ Fort Benning the US Army Marksmanship Armorer and repair van would be stationed on site. I can't tell you how many bent M16A1 barrels I saw changed and then the rifle could be zeroed. The troop couldn't Zero the weapon and then a Drill Sergeant would try to Zero it. If he couldn't, off to the van, get it gauged and then most likely changed. A lot were bent during use, but venture to say that most were bent prying the wire banding off of "C" ration cases.
I have never heard the specs you posted. Not even close.
On my initial qualification I went through two M16A1 rifles attempting to zero at 25m. The first had a faulty extractor and would not extract consistently.
The second would not come on target even with full windage. As a two time loser on the range, they sent me off to the “Weaponeer” to diagnose my marksmanship problem.
That was an hour standing in line watching candidates who could not shoot scatter a laser all over the screen with equally large groups while a sergeant tried to coach them enough to get a acceptable 25m group.
When it was my turn, I established my position and aimed at the target and proceeded to shoot a one dot group. The specialist running the machine started administering percussive maintence on it as the dot wasn’t moving. A major observing the proceedings started laughing. He asked me how I came to be in this line, and I told him the rifle related issues. He then further asked my prior shooting experience. I related shooting prairie dogs since age six, shooting small bore and service rifle in college and during three years in the USMC reserve. He ordered a sergeant to “get him one of the good ones and send him back to the range because he can shoot”.
Again, as noted before, I don’t doubt bent barrels happened and I clearly was given an M16A1 with a bent barrel. However my point was the rates of bent barrels was not as high as gauging with an armorers drop gauge would suggest due to the potential for a burr on the gas port to collect gilding metal from the bullet jackets and cause the gauge to hang up in the bore, resulting in a false positive indication of a bent barrel.
