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Thread: Ejection angle?

  1. #1
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    Ejection angle?

    I've seen the "pie chart" about AR ejection patterns and consider a useful guide to what *might* be the reason behind the way a particular rifle throws brass.
    However I keep in mind something else I read in here that the chart is not gospel, and while ejection angle *can* be indicative of how your rifle is gassed, it is not necessarily in and of itself diagnostic, and there are other factors that can determine ejection pattern.

    So aside from a straight-up overgassed or undergassed gun, or really hot or really weak ammo, what other factors contribute to ejection angle and why, and how do they manifest? For example, I've heard extractor tension mentioned as a factor in ejection angle but not an explanation of *how*?

    My question stems from a gun of mine that has started chucking XM193 brass fairly far forward, at about 1:00/1:30.
    However I'm skeptical the gun is overgassed. It's a BCM 16" midlength with a rifle RE/buffer/spring. This type of ejection when shooting M193 spec ammo is a fairly recent development, although I suppose with the round count (approx maybe 4k rounds at this point) perhaps I'm getting some gas port erosion now?

    The rifle has been and continues to be reliable, so I'm not trying to fix a failing gun, but the change in ejection pattern is puzzling to me and got me wondering about what other things besides gassing can dictate the way an AR throws brass.

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    That XM stuff is ridiculously hot and will tend to bounce off the deflector even on a correctly set up gun like yours. 4k is nothing for port erosion. I shot a bushmaster 14.5 carbine to 20-30k with the throat erosion being the only concern... and it still could have gone thousands more.

    I don't buy the throat erosion concern in that the top of the port still keeps the same inner diameter... so the gas is still choked down +/- a thousandth or two.
    "What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v

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    I figured it was probably pretty early in the game for port erosion but wasn't sure.

    I was actually under the impression that IMI M193 was even hotter than federal but I might be misremembering something that was specific to some lots of that Independence stuff and attributing it to IMI as a whole.
    I occasionally get popped primers with their 77gr as well.

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    Perhaps two years ago a "down the road" neighbor asked if I'd "sight-in" a new AR for him and teach him how to use it. Had a coyote he needed to get. He knew zero about it. "Sure". Though a wealthy man, he was / is a fantastic human being. Self-made and gtg. But I couldn't imagine him with an AR.

    He'd had this new AR for perhaps 2 years or so prior to. Purchased it at a lgs. Variable scope, S&W flat top. He gave it to me and a large box of Federal I think. Perhaps a loose box of 300 count (I think). The store had sighted it in for him. I first tore it down, cleaned and lubed it.

    Not even on paper (big paper) at 50 meters or 100 meters. I fairly quickly get it zeroed at 50. Bench shooting. The damn brass is tossing as close to 12:00 as possible. Not knowing much, I assumed it was a bit over-gassed and didn't give it much thought. The table was perhaps 30" from back (where I was seated) to front (toward the target). Sometimes the brass would just roll off the front of the table and other times it would land maybe 2-3 feet (at most) in front of the table. It functioned well, had good, consistent accuracy, etc. Had never experienced that before. I then taught him how to use and field strip the weapon in an AR 101 kind of way. Several months later, he reported to me he got that lone coyote. I see him frequently. he hasn't fired it since. Can't remember how much he told me he'd paid for his new rig but I do remember that he didn't even get a kiss in the process.

    Pretty sure it was Federal .223.

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    Quote Originally Posted by Circle_10 View Post
    I figured it was probably pretty early in the game for port erosion but wasn't sure.

    I was actually under the impression that IMI M193 was even hotter than federal but I might be misremembering something that was specific to some lots of that Independence stuff and attributing it to IMI as a whole.
    I occasionally get popped primers with their 77gr as well.
    IMI is notoriously HOT, so if its just with that ammo, try some other mild ammo and see how it likes some PMC for example.

    PB
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    Quote Originally Posted by Pappabear View Post
    IMI is notoriously HOT, so if its just with that ammo, try some other mild ammo and see how it likes some PMC for example.

    PB
    I shot a fair bit of PMC Bronze through it back when I first assembled it but I don't recall how it ejected. The gun was a pretty consistent 4 o'clock-ish ejector, including with M193, for a long time so it was just surprising to suddenly see it start throwing brass so far forward.


    Luckily the gun is working fine, the 1 o'clock ejection just made me wonder what other factors can contribute to determining ejection angle.

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    Quote Originally Posted by Circle_10 View Post
    I shot a fair bit of PMC Bronze through it back when I first assembled it but I don't recall how it ejected. The gun was a pretty consistent 4 o'clock-ish ejector, including with M193, for a long time so it was just surprising to suddenly see it start throwing brass so far forward.


    Luckily the gun is working fine, the 1 o'clock ejection just made me wonder what other factors can contribute to determining ejection angle.
    I just don’t know how the gun suddenly starts to run hotter. It usually starts to bog down if it’s mechanicly altered. But God only knows sometimes. I’m guessing it’s super hot IMI, keep us posted.

    PB

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    Quote Originally Posted by Pappabear View Post
    I just don’t know how the gun suddenly starts to run hotter. It usually starts to bog down if it’s mechanicly altered. But God only knows sometimes. I’m guessing it’s super hot IMI, keep us posted.

    PB
    The forward-ejecting stuff in this particular case is Federal XM193, but that's also pretty hot stuff so maybe it's just a particularly scorching batch. Although I have a couple of carbine gas guns that were throwing it about 3-4o'clock not too long ago.
    Again, not causing a problem at the moment, just had me curious.

  9. #9
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    Ejector and Extractor spring tension are the other main factors.

    Examine the bolt to see if anything seems different.

    Swapping the bolt or BCG can help isolate this to an issue with those springs.
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  10. #10
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    Quote Originally Posted by Clint View Post
    Ejector and Extractor spring tension are the other main factors.

    Examine the bolt to see if anything seems different.

    Swapping the bolt or BCG can help isolate this to an issue with those springs.
    So in those cases, is ejecting forward generally caused by strong or weak tension?
    I'm just speculating here because I'm no gunsmith and certainly no engineer, but is it something like a weak extractor spring allows the claw to slip off the fired case sooner after extraction, thus ejecting it sooner into the bolt's cycle, and the case goes forward as a result?
    Even if this doesn't apply to my gun I like to amass knowledge on things to look out for in future situations.

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