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Posted: 7/8/2010 7:47:09 AM EDT
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Hello all,
In my reading here and on other AR forums I've come to understand that a properly gassed AR ejects its brass to the 4 o'clock position. My Smith & Wesson M&P15T (16" barrel w/ carbine length gas system) ejects its brass to between 2 o'clock and 2:30, an indication that the weapon is over-gassed if I understand correctly. When new the ejection pattern was between 1:30 and 2 o'clock, it cycled smoothly, and recoil impulse was a touch sharper than I remember from the A2 rifle I used to own (though not overly so). After installing a Spike's Tactical ST-T2 buffer cycling became smoother still, recoil impulse is a touch softer, and brass ejection pattern moved back to the aforementioned 2-2:30 position. I've also come to understand that the carbine length gas system was designed for a 14.5" barrel and that the 16" minimum barrel length requirement for civilian weapons is not optimal for a carbine length gas system (thogh it seems that the vast majority of civilian AR carbines are 16" barrel / carbine gas system). Due to weight alone I may in the future swap the barrel out for a DD or BCM pencil barrel and swap the Troy free-floating MRF rail for something lighter in weight as well. I can give the mid-length gas system consideration at that time if I act on this thought. My question: Is an ejection pattern to the 2 o'clock position anything to be concerned about (indicative of an underlying issue with some negative impact, short or long term)? I'm perfectly happy with the perceived function of my AR - smooth cycling, soft recoil impulse, very accurate, 100% reliable after ~2,000 rounds and a variety of ammo. I know this isn't a big deal and I'm not looking to fix what isn't broken. I'm just interested to know what, if any, this ejection pattern says about how my AR is functioning. Thanks! 
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| The "undergassed" or "overgassed" thing is closely related to the particular load you're firing. A high velocity, high pressure load will inherently produce more gas pressure than a mild load. So you have to settle on what you'd call a "standard" load for your gun to determine whether gun has the right amount of gas pressure. Otherwise, you can expect the higher velocity loads to bounce brass off the deflector right smartly, while softer shooting loads should pop 'em off the deflector much more gently. When you get to the brass "sliding" along the deflector and still heading back, you're looking at a marginal load for your gas-operated gun. |
Thanks for the responses. I should have included ammo type used in observing this ejection pattern. The ammo used is Federal 55gr .223 FMJ. I'm really just curious what the ejection pattern might indicate, not worried in the least that there's any problem with the weapon. It runs like a top regardless of what I feed it! 
Thanks again! |
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Quoted:
Doesn't mean anything. There are other factors, buffer, spring, BCG weight(semi, F/A) wear. All effects it. As stated if the rifle is functioning fine just leave it be. There is no "problem" to fix. I was sure that nothing needed fixing - mostly just curious as to what the pattern might indicate. Thanks for mentioning the additional factors. I'm mostly looking to learn here. Further detail: * There's no unusual wear on the rim of any ejected case from the extractor or from hitting the deflector. * There are no permanent markings on the brass deflector, only occasional subtle traces of brass in the center of the deflector face that can be finger rubbed clean easily. * The recoil impulse is soft and cycling is very smooth - runs like the well oiled machine that it is. The varying answers make for interesting reading but, considering all of the variables, I'd say my AR is running just fine. Thanks again all! :) |
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