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Thread: Terminal ballistics-wise: Mk318 or M855A1?

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    Terminal ballistics-wise: Mk318 or M855A1?

    In keeping with the theme of this forum, I ask that question. When it hits a two-legged critter, which performs better and more consistently? Let's say for a military force, not Joe Civvie.

    Sure, M855A1 has some pressure issues which could make one default to Mk318, but if by some miracle increased wear on the weapon wasn't an issue, which one? Not talking barrier penetration, but I guess that should be included in the discussion.
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    Quote Originally Posted by ABNAK View Post
    In keeping with the theme of this forum, I ask that question. When it hits a two-legged critter, which performs better and more consistently? Let's say for a military force, not Joe Civvie.

    Sure, M855A1 has some pressure issues which could make one default to Mk318, but if by some miracle increased wear on the weapon wasn't an issue, which one? Not talking barrier penetration, but I guess that should be included in the discussion.
    1st of all M855A1 doesnt have increased wear anymore since they dropped the pressures. Both anecdotally and looking at ballistics gel, M855A1 seems to be the superior bullet. They are very close in performance but when the distances increase and velocity falls off, M855A1 looks to have a lower velocity threshold for fragmentation.

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    Quote Originally Posted by vicious_cb View Post
    1st of all M855A1 doesnt have increased wear anymore since they dropped the pressures. Both anecdotally and looking at ballistics gel, M855A1 seems to be the superior bullet. They are very close in performance but when the distances increase and velocity falls off, M855A1 looks to have a lower velocity threshold for fragmentation.
    I didn’t know that they did drop the pressure. I assume 855A1 is better at penetrating armor, I know it performed well there but I don’t know about 318 in that regard.


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    A1 is running functionally the same as legacy 855 pressure wise.
    A1 has a lower threshold of fragmentation
    A1 penetrates hard homogeneous targets much better
    I have personally found mk318 to be much more accurate. YMMV by lot number and barrel.

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    Quote Originally Posted by WS6 View Post
    A1 is running functionally the same as legacy 855 pressure wise.
    A1 has a lower threshold of fragmentation
    A1 penetrates hard homogeneous targets much better
    I have personally found mk318 to be much more accurate. YMMV by lot number and barrel.
    Any idea when this pressure reduction from the original loading took place? I have heard about it but never saw something specific like "After 20XX M855A1 underwent a change where the pressure was decreased slightly".
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    I know nothing about the pressure, but I have noted A1 to have higher velocities than greentip, along with slightly more recoil. Maybe I’ve only used older lots?
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    Quote Originally Posted by 1168 View Post
    I know nothing about the pressure, but I have noted A1 to have higher velocities than greentip, along with slightly more recoil. Maybe I’ve only used older lots?
    While I am far from an expert on ammunition development and procurement, I believe one of the goals of M855A1 was rifle ballistics from a carbine barrel. Of course, given current powder technology, the only way to achieve that goal is to crank up the pressure.
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    Quote Originally Posted by ABNAK View Post
    Any idea when this pressure reduction from the original loading took place? I have heard about it but never saw something specific like "After 20XX M855A1 underwent a change where the pressure was decreased slightly".
    M855A1 was getting tweaked so often it's hard to say, but at least 2 years ago.

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    Quote Originally Posted by WS6 View Post
    M855A1 was getting tweaked so often it's hard to say, but at least 2 years ago.
    Do you happen to have a link I can read on the subject? I'd be interested to see changes and timeframes.

    I don't recall where I read it but supposedly the pressures weren't dropped all the way back to "regular" 5.56 NATO, but nonetheless lower than the original recipe.
    Last edited by ABNAK; 05-02-19 at 18:14.
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    Pretty sure the pressure reduction wasn't long after it was introduced after all the reports of breaking bolts and wearing out barrels quickly. All the lots we've been shooting are older (2014ish) and don't seem noticeably hotter than M855.

    M855A1 fragments much further out than green tip, I haven't seen any hard data but from unofficial experiments people have been making with gel I wouldn't be surprised if it was past 300m. It's a huge improvement.
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