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Posted: 9/18/2014 10:37:33 PM EDT
| OK, let me start off by saying I've seen these threads before and I know the knee jerk response is "It's fine just shoot it." I realize that it's fine and I am shooting it. - I recently put together my first build. It's has a BCM barreled upper and BCM BCG. It fires and ejects reliably. Spent casings are landing at about 4 o'clock. With xm193 and xm855 the cases look fine but, I then bought a 100 round box of federal .223 and not only is it denting them low on the case but, the finish is chipped on my receiver where they are hitting. While I'm not thrilled by this, it's not a big deal. Aluminum doesn't rust. It does allow me to see right where the cases are hitting, though. They are hitting the sharp edge on the front of the brass deflector. So the question is - Why is this a problem with the (presumably) lower powered .223s and not the 5.56s? Is it possible that they are all hitting that spot and the federals have thinner cases and the 5.56s just take the abuse better? Maybe the federals have a thicker rim and the BCM BCG holds them longer causing them to impact the leading edge of the deflector instead of actually hitting the deflector where it's supposed to? Just curious if anyone knows what might be causing this. I don't care about the dented cases or really even the chip in the finish. It has worked flawlessly so far and I'm more than content to just keep using it but, I can't help but wonder what's going on. |
I would say the cartridge is underpowered or the rifle is undergassed, and that's why it's ejecting the way it is. Since it's federal .223 and not NATO-spec 5.56, I wouldn't worry about it too much, especially if you only plan on using that ammo for punching paper. If you plan on using it for a self-defense/home-defense application, I'd probably reconsider the ammo choice...I also wouldn't use it for hunting. But, that's just me. Hopefully that helps some. Ideally, with the round and all rifle parts functioning to spec and in harmony, the brass will pop out in such a way that it doesn't really make contact with the upper unless there's a tolerance issue somewhere. However, trying to tune it for that can lead you down ammo/spring/buffer/extractor ratholes that eat lots of time and money and don't really improve function in an appreciable manner... |
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Mine did basically the same thing between two different ammos and then it went away
I chocked it up to Slightly differing pressures = changing the ejection angle slightly Or the gun being new = things need to loosen up Or it wanted some lubricant Disclaimer Newbie’s assessment of his own issue …. Probability of  high
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| Under gassed for the .223 could very well be the issue. I have a st-t2 buffer in it , which seems to work well with the 5.56 but, is probably a bit heavy for the .223s. I've also got a "H" buffer. I guess next time I shoot it I'll throw that in and see if anything changes. I've fired a handful of tula through it, just trying different types of rounds testing for function and those locked the bolt back on the last round, cycled and ejected clear so, it can't be too horribly under gassed for the set up but, maybe just enough to cause this issue with the federals. Like I said before, not really concerned with it. Just curious what's going on. Thanks for the ideas. |
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Well, I guess I should have asked since it doesn't mention it anywhere - what barrel length? And rifle or carbine? I'm assuming carbine, since you mentioned H buffer.
If it's 14.5 to 16" or greater, you probably won't need more than a standard carbine buffer. If it's 14.5" and shorter, or exhibiting signs of overgassing (enlarged gas port, etc), H buffer. Shorter than 11.5" you'll definitely need an H buffer and you might want to investigate an H2 buffer, but only if you're showing significant signs of overgassing. You're definitely not overgassing..you're undergassing. Go back to an H buffer, or swap for a regular carbine buffer. Honestly, unless you're shooting thousands upon thousands of rounds and are going to be shooting the rifle well past the point where an armoror would swap out the barrel due to gas port erosion...don't get caught up in the aftermarket hype. Stick to a carbine, or an H buffer. If the carbine buffer makes the rifle seem overgassed, go to the H. You probably shouldn't ever need to swap in a heavier buffer than that. |
| AS already stated different ammo will eject differently, the greater the difference, the more you will notice it. I wouldn't let what you are seeing bother me one bit. As for the receiver finish wearing, if this bothers you, take a piece of 3M velcro, and stick a piece on the deflector. I have used both sides of the velcro with equal results. Just make sure you clean the surface real well to keep the oils and such from preventing good adhesion. Problem solved. |
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I didn't mean for that to sound as rude as it evidently did. I appreciate that you are trying to help. While I'm not real thrilled that it chipped the finish off the edge, it's going to end up getting a whole lot more beat up so, really it's not a big deal. Sorry I came across as being an ass. That wasn't my intention.
I came home and put the H buffer back in which, I hadn't tried with the .223s yet and no dents in the brass so, it was an under gassed/too heavy buffer issue. I'm sure a standard buffer would probably work even better with the .223s but, I don't have one to try out so, this is it for now. Thanks for everyone's help. |
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I hate to be a hard ass here, but there is one word in your OP that stands out. That word? PROBLEM You have no PROBLEM If your rifle fires, ejects the case, chambers a fresh round and does this repeatedly, regardless if the case is dented or where the case lands, you have no PROBLEM!! So much nitpicking, so much wringing of hands over nothing It is getting old |
| If it's so inconvenient for you to have this post listed in the ar basics (read, new and don't know very much) forum then maybe you shouldn't bother spending time reading and responding to it. The st-t2 buffer was too heavy and slowing down the cyclic rate to the point that the ejected cases weren't leaving the chamber with sufficient force to be thrown clear and instead were smacking the leading edge of the brass deflector (not the part intended to deflect brass) and bouncing off. While it did function, it wasn't functioning properly and had the potential to have actual cycling problems if a lower powered round was introduced. A switch to a lighter buffer resolved this. Question was asked, advice was given and situation was resolved. Pretty sure that's how this was supposed to go so, if that bothers you, maybe go start your own thread about how choosing to spend your time complaining is a waste of your time. |
OP, No worries, it's all good. Hard to tell sometimes when reading what someone is really saying. Don't worry about the others, some times folks forget what section they are in on this huge forum. If you don't like it, don't read it and certainly don't contribute to it, 
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Quoted:
http://i43.tinypic.com/271mx.jpg I would say the cartridge is underpowered or the rifle is undergassed, and that's why it's ejecting the way it is. Since it's federal .223 and not NATO-spec 5.56, I wouldn't worry about it too much, especially if you only plan on using that ammo for punching paper. If you plan on using it for a self-defense/home-defense application, I'd probably reconsider the ammo choice...I also wouldn't use it for hunting. But, that's just me. Hopefully that helps some. Ideally, with the round and all rifle parts functioning to spec and in harmony, the brass will pop out in such a way that it doesn't really make contact with the upper unless there's a tolerance issue somewhere. However, trying to tune it for that can lead you down ammo/spring/buffer/extractor ratholes that eat lots of time and money and don't really improve function in an appreciable manner... My rifle ejects between 3 and 2 o'clock according to the above chart. Is there any reason to try and correct the over gassing issue? Is it doing any type of damage that will eventually cause a problem with the functioning of the rifle in general? |
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Quoted:
My rifle ejects between 3 and 2 o'clock according to the above chart. Is there any reason to try and correct the over gassing issue? Is it doing any type of damage that will eventually cause a problem with the functioning of the rifle in general? What kind of ammo? Barrel length? Honestly, no, there's no real reason to try to "Correct" it...some rifles just shoot that way, even if everything's in spec. If the brass is shooting directly forward of me on anything 14.5" or longer I'd probably be a little concerned, and if the brass were coming out at 4:30-5:00 on an AR that didn't have a case deflector I'd probably be a little concerned I had oversprung it or had too heavy a buffer in it...but anything between 2 and 4, I wouldn't be concerned about. |
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IGNORE "THE CHART." It's only use (and minimal at that) is to help diagnose a FAILURE, not a rifle that consistently ejects and consistently ejects different rounds in different piles.
Here's how the ejection process works: as the BCG moves backward and the case clears the receiver, the ejector forces it to pivot on the extractor and leave the gun. When the carrier is moving fast, the brass moves backward fast enough to bounce off of the deflector and go forward. If the carrier is moving slower, the cases will slide across the deflector and continue to go backward. So lower powered rounds eject farther backward because they don't bounce off the deflector, while higher powered rounds bounce forward off of the deflector. Does that answer your questions? |
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Umm...I have an overgassed build that very definitely ejects forward, 1:30 or so. The brass does not touch the bump or the upper anywhere else. If it did, there'd be visible brass smears all over the thing...and there isn't.
I also had an undergassed carbine (16" barrel, cut down to 11.5 for an XM177E2 build, before anyone really made 11.5" pencil-profile barrels with the correct gas block area size on the barrel...even today, most are .750, not the correct .625). Undergassed to the point where it would barely lock back on an empty mag, but that's it. This was built on an A1 upper, no bump. I had brass smears all over the forward assist extrusion in the receiver. It was bouncing off of that. Shooting Wolf helped diagnose the issue, because it wouldn't even lock back on an empty mag it was so undergassed. Drilled out the port and viola...it now runs better. So, yeah, in my experience, that chart is pretty spot-on. |
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Quoted:
So, yeah, in my experience, that chart is pretty spot-on. Again, only if there's a problem. Your situations are a good case in point. Your "overgassed" gun probably was bouncing the brass off the rear of the ejection port, but without knowing how far out at 1:30 the cases were going, or where the bumps and dents in the cases were, it would be hard to figure exactly where. Since the carrier is moving backward the ONLY way for brass to go forward is to bounce off of something. |
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Quoted:
Again, only if there's a problem. Your situations are a good case in point. Your "overgassed" gun probably was bouncing the brass off the rear of the ejection port, but without knowing how far out at 1:30 the cases were going, or where the bumps and dents in the cases were, it would be hard to figure exactly where. Since the carrier is moving backward the ONLY way for brass to go forward is to bounce off of something. Quoted:
Quoted:
So, yeah, in my experience, that chart is pretty spot-on. Again, only if there's a problem. Your situations are a good case in point. Your "overgassed" gun probably was bouncing the brass off the rear of the ejection port, but without knowing how far out at 1:30 the cases were going, or where the bumps and dents in the cases were, it would be hard to figure exactly where. Since the carrier is moving backward the ONLY way for brass to go forward is to bounce off of something. Again - no brass markings on the upper, _anywhere_. Basically the case is getting shoved forward by the returning bolt/carrier before it actually clears the receiver. The cases didn't/don't have any dents in them, so if they are making contact on the way out, it's doing it in such a way that a) it's not leaving any brass behind, and b) it's not showing up on the case. This is not the first AR that I've had do that; hell, it's not even the first autoloader I've had do this. Fortunately, this one is timing out so that it actually works. With Wolf, it actually works a bit better; with M855, I'm sure it's only a few thousandths from getting jammed head first into the receiver. I'm sure as the spring gets weaker I'll see dents on the taper/shoulder of the case, where it starts to make contact with the front of the ejection port on the way out. Since in this particular setup it's not really tunable, it is what it is, and I shoot it regardless. (7.5" barrel, NEA PDW stock). |
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Quoted: IGNORE "THE CHART." It's only use (and minimal at that) is to help diagnose a FAILURE, not a rifle that consistently ejects and consistently ejects different rounds in different piles. Here's how the ejection process works: as the BCG moves backward and the case clears the receiver, the ejector forces it to pivot on the extractor and leave the gun. When the carrier is moving fast, the brass moves backward fast enough to bounce off of the deflector and go forward. If the carrier is moving slower, the cases will slide across the deflector and continue to go backward. So lower powered rounds eject farther backward because they don't bounce off the deflector, while higher powered rounds bounce forward off of the deflector. Does that answer your questions? |
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