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

  1. #21
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    Just a side note, hot brass in cleavage or similar is one of the main causes of shot bullet proof Glass Lane dividers in indoor ranges.

    Instructor friend of mine has seen it happen at one large local indoor range he worked at. It's also why they ban open toe shoes.

  2. #22
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    Quote Originally Posted by pinzgauer View Post
    Just a side note, hot brass in cleavage or similar is one of the main causes of shot bullet proof Glass Lane dividers in indoor ranges.

    Instructor friend of mine has seen it happen at one large local indoor range he worked at. It's also why they ban open toe shoes.
    Ive been swept with fingers on triggers by the hot brass down a bra many many times, itll put you on the ground for sure. Ive had it down my sleeves whilst in prone, and down my shirts myself but thankfully my first thought is to get my finger off the trigger & not sweep the area. It does really hurt.
    The obedient always think of themselves as virtuous rather than the cowards they really are.

  3. #23
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    Only helmet testing I am aware of is penetration at 1000 yards. We had a rack about six feet square and the steel pots were put on it and you shot and shot till a round went through the magic window on the side.

    Had not noticed there is pages missing in report.

    As a interesting side note we use US Helmets and the Brits test using German WW2 helmets.
    Last edited by Humpy70; 01-03-20 at 14:58.

  4. #24
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    Humpy70-

    Can you speak a little more on the extreme spread in barrel life? You said that most of the barrels where losing practice accuracy around the 4k mark, but with the FN made ammo they where lasting to 12k? If something as simple as switching powders can triple the barrel life, why isn't that being looked into more?
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  5. #25
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    Quote Originally Posted by lysander View Post
    1-14 to 1-12....
    Thank you guys I messed up doing 3 things at once.

  6. #26
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    Quote Originally Posted by Humpy70 View Post
    Only helmet testing I am aware of is penetration at 1000 yards. We had a rack about six feet square and the steel pots were put on it and you shot and shot till a round went through the magic window on the side.

    Had not noticed there is pages missing in report.
    I'll have to check and see if I have any of the old articles. 1000 yards makes more sense as it was a silly test not relevant to modern warfare.

    I would think that just about any of the five five six rounds would penetrate the steel pot at 200 m, so your memory is probably right.

  7. #27
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    Turnburglar, You are absolutely correct. There used to be a bumper sticker that said, "Crime wouldn't pay if the gov't ran it." Insofar as ammo its not that easy to change propellants on a high speed loading line.

    The US uses SCAMP lines at Lake City that manufactures bullets, cases, seats primers, inserts propellant and laser gages at the rate of 4 rounds per second and they can put out 77 Million rounds per day on 386 which is the term for war production, 3 eight hour shifts a day, six days a week and the tooling is replaced on Sunday. The lines are tuned so to speak for WC846 as it meters good and falls quickly. IMR 8208 stick propellant used to be used on the manual lines that are much slower and I suspect it would hold up better.

    Testing is fired in 120 rd segments per rifle, two mags 3 shot bursts, two mags semi auto at a specific firing rate and then subjected to forced air cooling.

    Competition AR shooters told me they replaced barrels at 2000 rounds and I saw a segment on the Army MTU that said they replaced barrels every 700 rounds and they are using all handload for custom load ammo and those rifles shoot exceptionally well.

    On 7.62 and 30.06 bolt gun rifles guys tended to change barrels between 4000 and 5000 rounds but they see a rough life.

    I saw a ammo test rifle at Benning that had been shot so much that there was no visible rifling 3" forward of the chamber. They cut barrel off 3". Rechambered and it still shot same groups. IIRC that barrel from a hard mount would print under 1.5" at 300 yards.

    As we both know ARs are not the easiest nor fastest weapons to clean where theoretically you can clean a bolt gun after every yard line.

    Read the attached test report above and it will give you more details. Start on page 25 and read through 42 and you will get a idea of intensiveness of the testing at Aberdeen and how meticulous the TOPs TEST OPERATION PROCEDURES. To be sure you will see dispersion measured in centimeters and the intensity of that is phenominal.

    As a general rule ball propellant is known to be more erosive on barrels. The 12,000 round life ammo was loaded by FN and I don't know what it had loaded therein but our ammo was loaded with WC846,.

  8. #28
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    Was there a switch to WC846 at some point? The 1994 print of TM 43-0001-27 lists WC844(H335) as the main or only powder for most 5.56 loads and WC846(BL-C(2)) as the main powder for several 7.62 loads.

  9. #29
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    Small Arms Ammo Pamphlet Frankford Arsenal printed 1967 calls for IMR 8208M 25.5 gr. WC846 28.5 gr. for Ball M193. Maybe they finally changed as the ammo side of our branch badmouthed 846 so maybe they went to WC844 in later production.

    7.62 Ball calls for WC846 46 gr. and IMR 4475 at 41 grains for M59 Ball in same pamphlet. Remember conversation with chief of ammo there was this one guy in the chain that was ape for 846, maybe he retired and it was changed over.

    Both of these are nominal charges and are adjusted up/down depending on the burn characteristics of the different lots.

    I wish I had a 100 lb drum of IMR 8208 though. I will email the retired Chief of ammo who is retired in Florida and see if I can pin the dates down as to change. He retired about 8 years ago.

  10. #30
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    This thread is amazing. I like to learn the reasoning and the history behind different machines. Just like the finger grove on the pistol grip on the A2 which I read on TOS.

    Dan
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