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

  1. #61
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    Lysander you forgot one requirement. A politician had to benefit from it being bought.

  2. #62
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    Awesome thread. Thanks Humpy70
    “I prefer dangerous freedom over peaceful slavery.” – Thomas Jefferson.

  3. #63
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    Thank you. Glad you enjoyed it.

  4. #64
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    Just remembered another incident. M1911A1 replacement slides were required to be proof fired and marked and we got one in certified proof fired and marked but it has never had the hole drilled for the striker.

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    Humpy70, a statement you made earlier, about ball powder burning out barrels faster than stick powder, do you have a source? I was always under the impression than ball powder was easier on barrels because it burned cooler. I look forward to your reply.

  6. #66
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    Yes, it is a known fact in the small arms test field. Every new variant of ball propellant is loaded with the candidate and it is sent to Aberdeen where it is tested for initial dispersion with a MG in a hard mount. When I was there it was M60 LMG. I suspect now it is the M240. Groups are fired and measured.

    Then the weapons go to the cold room and it is heated I believe 140F but I have a recollection it might have been changed to 160F. They fire 50 rd bursts for 10,000 rounds per weapon and they go back and check them for dispersion again. If the groups increase to 150% it is rejected. If the yaw cards reveal 15 degrees or more at 1000" it is rejected of if velocity drops 200 fps it is rejected. Normally the yaw is the rejecting factor or dispersion. I don't remember velocity deterioration ever failing when I was there. It was determined many years ago that high temp testing is the worst thing we could do and rather than go through all the other testing, doing the worst first was done to save money.

    As I left they had just failed a new ball propellant and 330,000 rounds was being sent to the burning ground, dumped out of cans, piled up and soaked with diesel fuel and lit off.

    I remember there was a symposium at Camp Perry about 25 years back and a rep from Sierra was speaking and someone brought up they had heard that ball propellant was marvelous and the Sierra rep asked a general question to the audience of how many top shooters used ball propellant and no one could name one.

    I have some WC852 slow I load and the pressure curve is so slow on it that it makes velocity well before it maxes out on pressure. SLOW was restricted to 30.06 ball/tracer designated for Cal 30 BMGs as they are not gas operated.

    In the M16A1E1 Test (adopted as M16A2) the barrels were right at rejection at 4800 rounds and well beyond rejection at 6000. In the re-test the same results were duplicated but the guns that ran the SS109 ammo were still in spec at 12,000 rounds but right at rejection point which is what the USMC speced they wanted.

    Any manufacturer of ball propellant you question just drop them a line and ask they what numbers they make have been certified by Aberdeen Proving Ground for acceptance for US spec ammo and what ammo is loaded with their product. WC844 was in but I now understand WC846 has replaced it. I am not aware of WC846 availability over the counter for commercial sales but have seen some surplus sales of small amounts.
    Last edited by Humpy70; 02-07-20 at 23:55.

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    ^Sorry, but I am going to have to disagree with some of this.^

    According to Frankford Asenal, Ball propellants average lower flame temperatures and prolong barrel life.

    In Frankford's "History of the Development of Ball Propellant for Small Arms" by M.E. Levy the following data was presented:

    In .30 Caliber: (all averaged over 5 weapons)
    Plain barrels - (300 round bursts at 2 minute intervals)
    Ball - 1322 rounds
    IMR - 937 rounds

    Chrome plated barrels - (300 round burst at 2 minute intervals)
    Ball - 1853 rounds
    IMR - 1321 rounds

    In 20mm:
    Chrome - (50 round burst at 2 minute intervals, complete cooling after 600 rounds)
    Ball - after 2400 rounds the velocity drop was 90 fps
    IMR - after 500 rounds the velocity drop was 200 fps

    This report also gives other calibers from experimental Cal. 60 through 30mm, and all of these show that ball propellants always show a longer useful barrel life. Further, this report recommends that all US military ammunition be loaded with ball propellants, where practical, DUE THE THE FACT THAT BALL PROPELLANTS SHOW IMPROVED BARREL LIFE.

    A recommendation that the Army seems to have taken, as ball propellant loading are far more common than any other propellant type, at least in small arms (through 30mm).

    In Frankford's "7.62mm Barrel Life as Affected by Certain Inorganic Constituents and Bullet Design" the following was published:

    Ball propellants: 18,325 to 17,300 (variation due to anti-wear additives)
    IMR propellants: 14,500 to 8,000 (variation due to anti-wear additives)

    And, last for now, is from Frankford's "Thermochemical and Burning Rate Properties of Deterred US Small Arms Propellants"

    Adiabatic flame temperatures of the deterred propellants:

    WC846 - 2193 to 2244 degrees K
    WC870 - 1978 to 2081 degrees K
    IMR 4227 - 2537 to 2550 degrees K
    IMR 4350 - 2605 to 2622 degrees K
    IMR 8138M - 2358 to 2406 degrees K
    IMR 4895 - 2287 to 2310 degrees K
    IMR 5010 - 2580 to 2593 degrees K
    CMR 160 - 2338 to 2373 degrees K

    As you can see all of the extruded propellants show higher flame temperatures (an average of 340 degrees hotter) than the ball propellants.

    There are a few other reports specifically on the 5.56mm barrel life with ball WC846 and WC844 and IMR8208 propellants that also show that ball propellants consistently provide longer barrel life. And, a bunch more from the 1950s and 1960s that show that ball propellants are generally better at reducing wear, but sorry. I don't feel like rooting through my library to find them, I think the point has been made. There might be some new ball propellants that don't make the grade, but of the ones that do, and did, they all show reduced wear compared to their stick competitors.

    The limits for a "worn-out barrel" are a velocity drop in excess of 200 fps or a yaw angle of more than 15 degrees in 25%, or more, of the rounds for all of the above tests regarding barrel wear.

    EDIT: The original loading for 5.56mm was WC846, same as 7.62mm. When calcium carbonate deposits were found to accumulate in the gas tubes in hot, humid conditions with certain lots of propellant with high CaCO3 content, a reduced CaCO3 blend of WC846 was made just for 5.56mm production under a different dash number. Later this was split off as WC844
    Last edited by lysander; 02-05-20 at 21:25.

  8. #68
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    First, let me say that myself and all of the readers really appreciate you sharing this information with us.

    Quote Originally Posted by Humpy70 View Post
    They fire 50 rd bursts for 10,000 rounds per weapon and they go back and check them for dispersion again. If the groups increase to 150% it is rejected. If the yaw cards reveal 15 degrees or more at 1000" it is rejected of if velocity drops 200 fps it is rejected. Normally the yaw is the rejecting factor or dispersion. I don't remember velocity deterioration ever failing when I was there.
    This is great info. I am curious, were they firing the gun in the three round burst mode and if so for how many magazines before it was allowed to cool?

  9. #69
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    I am not familiar with M E Levy work, what year was that published?



    What I am referring to is what was done at Aberdeen as of 1983 when I left. There was a Test Operation Procedure in place at that time to test as I indicated above. Frankford Arsenal had closed in the mid 70s and the personnel that did not retire immediately transferred to Picatinny. The Chief of the Army Small Cal Lab was formerly a ammo engineer at FA and he told me a lot of interesting facts as he was also assigned to the M16 when it was first adopted.

    On the M16A1E1 two mags were fired in 3 shot bursts and two mags fired in semi auto which totaled 120 rounds and the barrels were forced air cooled before the next 120 round string was reconducted. There was a firing schedule and I believe the 3 shot bursts were spaced every three to five seconds.

    The hottest temp the M16A1E1 attained was in the cook off test which was single shot 500 rounds in 500 seconds and 501st round was chambered and a stop watch started. Barrel temp was in the 400°F range. Cook offs were attained in 8-10 seconds as I remember.


    Startng at zero rounds and then every 1200 rounds the weapons went to Metrology Lab and a complete series of measurement were made and it was very quickly determined the barrel throats were wearing much faster with the XM855 ammo. The wear was so fast the erosion gage measurements went past the rejection point much quicker with the ammo loaded by Lake City. As well the yaw data confirmed what we were getting in our firing out to 800 Meters.

    With the XM855 at the 6000 round point we could not hit the target paper much less the entire target board 8ft wide and 12 ft high at 800 or 700 meters and at 600 meters the dispersion was recorded on the target board. With the SS109 loaded by FN with the same projectiles the dispersion was in spec to 12,000 rounds.
    Last edited by Humpy70; 02-06-20 at 05:02.

  10. #70
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    Quote Originally Posted by Humpy70 View Post
    I am not familiar with M E Levy work, what year was that published?
    The date was in the late 1950s, when the Caliber .60 was going to be the next aircraft gun....

    Quote Originally Posted by Humpy70 View Post
    What I am referring to is what was done at Aberdeen as of 1983 when I left. There was a Test Operation Procedure in place at that time to test as I indicated above. Frankford Arsenal had closed in the mid 70s and the personnel that did not retire immediately transferred to Picatinny. The Chief of the Army Small Cal Lab was formerly a ammo engineer at FA and he told me a lot of interesting facts as he was also assigned to the M16 when it was first adopted.
    The fact that people moved to New Jersey does not change the flame temperature of a given propellant. I provided the flame temps, and they are what they are. It is well established that higher flame temps equal faster throat erosion.

    Quote Originally Posted by Humpy70 View Post
    On the M16A1E1 two mags were fired in 3 shot bursts and two mags fired in semi auto which totaled 120 rounds and the barrels were forced air cooled before the next 120 round string was reconducted. There was a firing schedule and I believe the 3 shot bursts were spaced every three to five seconds.
    That is the standard test firing protocol for burst equipped M16/M4s. For full-auto equipped M16/M4s the only change is the full auto magazine is a 30 round mag-dump. That firing schedule is used for acceptance tests, any barrel wear tests, and reliability test.

    Quote Originally Posted by Humpy70 View Post
    The hottest temp the M16A1E1 attained was in the cook off test which was single shot 500 rounds in 500 seconds and 501st round was chambered and a stop watch started. Barrel temp was in the 400°F range. Cook offs were attained in 8-10 seconds as I remember.


    Startng at zero rounds and then every 1200 rounds the weapons went to Metrology Lab and a complete series of measurement were made and it was very quickly determined the barrel throats were wearing much faster with the XM855 ammo. The wear was so fast the erosion gage measurements went past the rejection point much quicker with the ammo loaded by Lake City. As well the yaw data confirmed what we were getting in our firing out to 800 Meters.

    With the XM855 at the 6000 round point we could not hit the target paper much less the entire target board 8ft wide and 12 ft high at 800 or 700 meters and at 600 meters the dispersion was recorded on the target board. With the SS109 loaded by FN with the same projectiles the dispersion was in spec to 12,000 rounds.
    I have read the report on the M16A1E1 tests done in 1983, "Technical Test of M16A1E1", (Humphreville, Newhouse, Feb 1983). It details most everything.

    However, in this report, the authors state that it is the FN produced XM855 that showed about 25% worse dispersion than the control M16A1s shooting standard M193 (ball propellant). Also it notes:
    ...the XM855 ammunition as loaded by LCAAP showed poor quality . . . not only was outward appearance of the ammunition poor, but the performance was poor...several occasions rounds failing to reach the target...
    So, perhaps this is the reason for other failures.

    I do also, have a report on a test of a proposed alternate propellants for M855/SS109 that weren't approved also from that approximate time frame.

    But, in general, ball propellant is so loved by the Army because it reduces barrel wear, even if it doesn't always show the best accuracy, or is pretty dirty. There are many report dating as far back as 1950 to just a few years ago (2010), that show ball propellants are much easier on barrels.
    Last edited by lysander; 02-07-20 at 10:36.

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