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Thread: ARs didn't really need to have 1-7" Twist and how it was determined that they would.

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    ARs didn't really need to have 1-7" Twist and how it was determined that they would.

    The M16A2 began life as the M16A1E1 meaning M16 Amendment 1 Experimental Mod 1 and it was the USMC Firepower Division, Quantico, Virginia that got the program rolling The Marines detailed a Maj Dave Lutz to the Joint Services Small Arms Section (JSSAP) at Pictinny Arsenal, NJ who got it rolling and Maj Bruce Wincentsen was named Project Manager for the Corps and they wrote up specifications they wanted the improved M16A1 to meet which exceeded the ability of the M16A1 to meet.


    This consisted of several variations, heavier barrel, longer range capability, better Fire Control ( which is military terminology for Sights), improved forward handguards, longer butt stock, modification of the ejection system to preclude left hand shooters from being struck by hot brass, the plastic was changed to allow the launch of M31 Rifle Grenade and there was a large stockpile of grenade launching cartridges fabricated for the M16A1 but could not be used as firing the rifle grenades caused stock failure on the first shot 98% of the time, heavier bullet, longer barrel life (12,000 rds), flash suppressor re-design to keep dust from being disturbed by muzzle blast giving the shooters position away and a 3 shot burst system.

    I was told by Wincentsen that the Firepower Division wanted to do away with full auto capability all together and the 3 shot burst was a trade off as a couple of Generals thought it was needed. Had they queried the Army Material Systems Analysis Activity and obtained guidance from them chances are they would have gone with semi auto only as full auto fire at human size targets at 25 yards in 3 shot segments will give you a center hit on shot 1, a grazing it or miss at the top of the shoulder and another miss about two feet higher. Thus there was massive data that confirmed this compiled by AMSAA over the years.


    We had a definition of "Firepower" at the Army Small Cal Lab which was "Firepower=More Misses Per Minute."

    In early 82 I was directed to go to the Conference Room at Test & Evaluation Command HQ at Aberdeen for a meeting about a new M16 inbound for testing and I went over to TECOM HQ and walked into the conference room and Wincentsen was standing there. We looked at each other and we broke out in big friendly grins as we had been shooting competition together from local matches at Quantico to the National Championships at Camp Perry. I forgot to add that Wincentsen had been a firing member of the Marine Corps Rifle Team for years and he was quite good.


    Wincentsen asked me what I was doing there and I told him I was going to be the Test Director for a new M16 system and I asked him what he was doing there and he said he was the Project Manager and that I had just made his day. He went on to explain that he had told TECOM he wanted to interview who was going to run his test and know their qualifications as he wanted nothing less than a NRA Highpower Competitor running his test and when he saw me he knew I exceeded his expectations as I held NRA Master Class ratings in Highpower Rifle and Smallbore Rifle. Thus he only asked me one question, "what is your home phone number--- here's mine". The TECOM Liaison Rep walked in and Wincentsen told him we had been shooting together for at least 8 years and that I "would be fine."


    The rifles came in from Colt with the above Mods and equal number of M16A1s new condition came in and I started the "Test Operation Procedure" TOP. Wincentsen called me and asked if I could come down to Quantico and to observe the testing he was conducingt with a Marine Squad and a Army Squad and if I was going to be free for a few days to come down. I told the section chief and I went down and spent about four days at Quantico and Wincentsen and I were together from 0700 till we got through then I followed him home to Stafford and had dinner with him and children and their children every evening.


    The testing was to consist of a vast multitude of sub tests and some did not include firing. The firing consisted of initial targeting, at 100 to 800 Meters, then we fired more rounds till we had 1200 rounds on each M16A1E1 and M16A1. At 1200 rounds the rifles were measured for throat erosion etc and the whole series happened again stopping at 2400 rounds per weapon, then at the 3600 round point, and 4800 round point.

    I noted very little change in dispersion at 1200 and a minimal increase at 2400 rounds and a noticeable increase at 3600 and a massive increase at 4800 rounds which was right at rejection was 7.2" at 100 yards. I had fired another 1200 rounds which made 6000 rounds and we were going to fire the 100-800 Meter Dispersion the next morning (Saturday) and I was in the office and Wincentsen called me to let me know he had a meeting with Commandant USMC 0900 Monday and he was going to recommend a buy on the system.


    That presented a problem as I was not allowed to discuss with anyone outside my section how they were doing unless I was asked a direct question and I tried to warn Wincentsen by asking how many rounds he had on his rifles and he said 2400 and I told him I had 6000 and we were going to target them the next morning hoping he would ask me a direct question I had to answer but he didn't catch my question.

    Well the next morning the barrels were so bad that a Marine Master Class shooter nor I could keep them on the 8ft X 12 Target at 800 and 700 meters and at 600 we covered the entire board and I stopped the test and released the Marine shooter to go back to his motel with a six pack and watch the ballgame the rest of the day.


    I tried calling my Supervisor all Saturday and all Sunday as well as the TECOM Liaison Officer and neither were home and I knew it was not going to look good for Wincentsen if he went to the meeting Monday AM and right after lunch message traffic arrived that all the barrels were shot out. I knew that was not going to make Wincentsen look good thus I called Wincentsen at 2200 Sunday evening and he was very appreciative that I had called to warn him and thus he changed his presentation.


    In the interim we defouled the barrels, air gaged the barrels, borescoped them, took flash X rays of bullets in bore, cut one down the middle from muzzle to chamber and determined the lead edge of the rifling was worn down even with groove thus we had rifling that looked like ratchets.

    I called Wincentsen at work and he was out and talked to his Gunny assistant and asked him if he knew why the barrels were 1-7" twist and he told me that Wincentsen have given him the specs for the new FN 5.56 MG and he was told to go through it and copy the MG barrel specs which called for 1-7" thus were copied. Had the M16 engineer in charge at Rock Island been asked it would probably have been 1-9". Bottom line was 1-7" was put in because that was in a flier Wincentsen handed the Gunny and that was all there was to it.


    The new FN 5.56 MG was undergoing testing as well and was not giving troubles and I knew it had 1-7" because that was the twist rate required to stabilize the SS110 FN Tracer round that was loaded with a much longer tracer projectile. Since tracer is not issued to infantry there was no need for 1-7" but that is how it was arrived at and involved no slide rules or anything exotic.


    A conference was called and the M16 Engineer in charge (from Rock Island) came, a rep from JSSAP, another Test Director from my office, Wincentsen and there was about five others I never saw before or since and don't know who they were. Everyone examined the targets and the M16 Engineer informed the group 1-7" was too fast for the SS109 and 1-9" would have been better but there were no 1-9" barrels to be had.

    Subsequently the decision was made to retest exactly as before, retest with M193 55 gr. ammo, the M16A1 and 100,000 rounds of MG (SS109/SS110) ammo arrived from Canada that was loaded with 62 gr ball and tracer ammo in belts and first we had to hand delink 100,000 rounds and thusly 10,000 rounds per day were expended for 14 days. The funny part is the Canadians gave us the ammo but wanted their ammo cans back. I don't believe they got them all back as our guys really liked them.


    Note: FN made 62 grain bullets were loaded by Lake City using WC846 (same as M193) powder thus the only difference between the US and FN loaded ammo was the powder which took out barrels at a faster rate but the M16 Spec only required a 6000 round barrel life. Bottom line was it was proved the FN loaded ammo was amazingly good quality and it being originally loaded for machineguns in Canada meant it was not a select lot thus if you ever run up on green tip 5.56 that has FNB headstamp get every last round your budget will allow as it is as good as our M118 Match ammo in 7.62.


    This gave us some very interesting results which we retested and the Lake City loaded ammo took out barrels exactly as before, the M193 took about barrels but not as bad and the SS109 ammo was the best ball ammo I had ever seen and the barrels were right on rejection at 12,000 rounds where they were right at rejection at 4800 rounds with US loaded ammo by LC using FN made 62 grain bullets and our WC846 ball powder.

    Thus the only thing left was to write the report. There were several more problems that surfaced in testing that were identified. One was the indent delivered by the hammer to the striker that went forward and ignited the primer was slightly below spec. The requirement was .022" indent on copper cylinders and rifles tested exhibited energy that gave .020-.021" range and we had like five failures to fire in 244,000 rounds. The misfire rate on normal ball ammo is expected not to exceed one misfire in one million rounds

    .
    One rifle broke in half in the drop test which broke off the ring at the back of the lower receiver that the buffer tube screws into thus if you compare the new lower receivers to the M16A1 or the Colt Commercial ARs of the day you will note they are much thicker now with obvious reinforcement.
    All systems undergoing testing are evaluated against two DoD standards at Aberdeen Proving Ground and the first is the Military Standardization Handbook of Human Engineering which calls for hot case ejection to eject cases between 1:00 and 2:00 in the first quadrant (right of bore line). Obviously everyone knows M16s/M16A1s directed expended cases from 2:00 to 5:00 which is a 90 degree fan and a large number of left hand shooters were struck in their right cheek by hot cases from adoption to that time as was I many times as I shoot from left shoulder and have had nicks cut out of my cheek and no one has ever explained to me why it was accepted in the 1960s being in violation of the above standard and when it was upgraded to M16A1 it was not fixed. I don't know the time frame the M16A1 was phased in.


    I know the M1 rifle case ejection had to be addressed to meet the standard in the 1950s. As well the M14 had to be changed as I knew the Engineer In Charge (Al Cole) and the chief draftsman (Julio Savioli) of the M14 project worked ten feet away from me when we were both in the Special Projects Group at Picatinny and he told me a lot of interesting things about the M14. One of them was they had to add metal to change the shape of the op rod specifically to change the ejection from 3:00 to deliver cases between 1:00 and 2:00 to meet the above requirement. Al Cole had left the Small Cal Lab and went to Ruger about three years before I arrived and I met him when I went to Ruger Armorer's School and I talked to him up till about 91.


    The M16A1E1 had the "bump" behind the ejection port which changed the brass ejection from 2:00-5:00 (90 degree fan) and it became 2:00-4:00 o'clock (60 degree fan). On my trip to Quantico I saw them being fired by troops on Lloyd Range and hot brass rained down on personnel to the right thus I identified it in my report.


    When my Section Chief read that in my draft he became concerned and directed me to call the Army Safety Center, Ft. Rucker and ask them if there had been any hot brass injuries and I did so and I will remember that call the rest of my days. I told the individual that answered the phone I was testing a new M16 variation and that there was a change in brass ejection to protect left hand shooters that caused 1/3rd more hot brass ejections to fall in the reduced 60 degree fan..


    He told me he would go pull the M16 file and go through it and call me back and he did and a half hour later and he told me that two troops had been killed and one wounded (as of December 82) and I was shocked. I asked him what happened and he said all three reports had adjacent shooters to the right received hot brass impacts that went into clothing and the recipients went into gyrations to stop the burning and they pulled the triggers while pointed at adjacent personnel on the line and they were shot.


    I immediately went to Supervisor's desk and told him and he was shocked as well and he directed me to fill out a MEMO OF TELCON form and document who I talked to, what was said, describe the shootings etc as it was going into the report.
    Neither of us could understand why this information had not come forward prior as that is exactly what Product Engineering is for to evaluate problems and recommend changes and that is the area I worked when I first went to the Army Small Arms Lab. I was in charge of the M1, M14 and other rifles and the M16 engineer was about twelve feet from me. I have called him and he confirmed he was never informed of such and he was there from 77 up until mid 90s.

    My Supervisor had started writing as I wrote up the MEMO and when I got through he read it and said it is going in the report and he showed me what he had written and I got introduced to MIL STD 882a which I had never seen which was:
    MIL-STD-882, DEPARTMENT OF DEFENSE STANDARD PRACTICE: SYSTEM SAFETY
    This is a very interesting document that developers are required to adhere to and lays out how systems are graded as to severity and injury and such evaluation is required by test personnel if they suspect something might go wrong when the system was fielded. Thus in this instant there had already been deaths and shootings in the M16, M16A1 and the ejection pattern of the rifle designated to be the M16A2 (if adopted) was going to present even more hot brass towards adjacent personnel to the right.

    https://drive.google.com/open?id=0B3...ZTT19YckY4d2ow

    The above is the grading criteria of MIL STD 882a in use at that time and it put in and highlighted in RED so you can see how problems are graded. In the latest revision the same criteria is presented but this form is not used for some reason but the grade 1C has not changed.
    We both signed the transmittal document and it went to printing and I left the Proving Ground for a position at the Federal Law Enforcement Training Center which put me much closer to my home in SC as my Dad was 73 and I wanted to be closer to him and I did not receive a copy of the report before I left.

    I saw my first A2 in 1985 at the National Rifle Championships and noted the same bump was in place and hot brass was raining down on adjacent shooters to the right and I have seen all the variations since and they all exhibit the same design flaw and is yet to be corrected. I have subsequently talked to others who have seen folks shot/killed as a result.

    To give a better understanding check below picture out. It shows a M16A4 firing a 3 shot burst and the camera operator has moveed just far enough to the rear to miss the 4:00 ejection pattern. As you can see the first case has ejected and the second has just ejected but the bolt hasn't gone forward to pick up the third round yet.

    https://drive.google.com/open?id=0B3...A2NHVFcjRaRHNv
    So that is the good, the bad and the ugly so to speak of the A2 and beyond.
    Last edited by Humpy70; 02-22-20 at 15:16.

  2. #2
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    Will the M856 tracer stabilize with less than 1/7?


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    It might do it in warm weather but unlikely at 60 below zero. Then again they don't necessarily group with the M855 at the longer ranges and not likely to go in a 55 gal drum at 600 yards. They would be ideal home defense round in either a A1 or later as the terminal effects would be awesome with it tumbling.
    Last edited by Humpy70; 01-02-20 at 12:46.

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    That is really interesting about the brass ejection pattern being considered a lethal liability considering the modern cultural obsession with obtaining a "proper" 4 o'clock pattern by fixing overgassing issues on modern commercial carbines with oversized gas ports. Also found the requirement of a longer stock interesting now that collapsible stocked carbines are the standard for body armor wearing troops and the small statured.

    I trained on A2's back in 1995 OSUT so this history is a fascinating trip back in time for me.

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    I have an article from a magazine H had from 1962 about how the 1 in 10 barrel wouldn't stabilize the mil spec bullet at below freezing temps or some thing like that so the spec was changed to a 1 in 12. The article was from a May 1962 The American Rifleman Yes I am that old.
    Last edited by SteveS; 01-02-20 at 13:16.

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    I assume there was a change in forearm material with A2 development, but the cylindrical/ribbed forearm showed up in the 1960's. Thread has several M16 magazine article jpegs in it.

    http://www.usmilitariaforum.com/foru...-rifle-manual/

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    I joined the Marines in 1979, of course that was while the M16A1 was our rifle.

    I liked the A2, but over time I got the feeling some of the 'improvements' had more to do with better rifle range scores, than better ergo's as a fighting weapon.

    It seems that as time progressed, we now have the M4, and similar, that have evolved very well into the role of fighting weapon.

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    Quote Originally Posted by SteveS View Post
    I have an article from a magazine H had from 1962 about how the 1 in 10 barrel wouldn't stabilize the mil spec bullet at below freezing temps or some thing like that so the spec was changed to a 1 in 12. The article was from a May 1962 The American Rifleman Yes I am that old.
    I think you mean the change was from 12" to 10" twist.

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    Quote Originally Posted by Mysteryman View Post
    I think you mean the change was from 12" to 10" twist.
    1-14 to 1-12....

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    Humpy70,

    Your experience is absolutely unique and very humbling for most members here. Thank you for the interesting insights and sharing your experience.

    It's always interesting to read your posts and what went (and probably still goes) into the small arms development. Thank you!

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