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Discussion Starter #1 (Edited)
I need an Iowegan, or substantially identical expert.

Here's the situation. I built an M4ish carbine last fall, I finally got it out to the range over the weekend and it shoots great, accuracy is fantastic too, but there is one tiny tiny thing that my OCD cannot overcome. The brass is landing at between 1 o'clock and 2 o'clock, but mostly closer to 1 o'clock. I say landing instead of ejecting because now I'm not entirely sure what the cause is.

My first thought was that the system is overgassed and is ejecting forward. AT least that is what the brass ejection pie chart suggests.



After referencing the above chart for the possible "fixes" , I determined that a heavier buffer would solve the problem. The rifle is already fitted with a FA M-16 BCG. After I asked the experts at another forum how much more weight I should use, well, that's when the cause of the effect became less clear.

At this point I should probably give some specs on the rifle. The barrel is a Radical Firearms 16" CPQ melonite, 5.56 M4 profile with a 1:9 twist, carbine gas system, barrel diameter at gas port .750", and a PSA FA NiB BCG. Carb extension tube with standard 3oz. buffer (note, the 3oz buffer actually weighs 2.85oz). The gas block is a two piece YHM flip up front sight. Technically, the combination should produce a perfect ejection pattern assuming everything is in spec.

Well, as it just so happens, the gas port on the barrel may be out of spec. I contacted Radical to get the port spec and was told they drill it to .089". Then I referenced that with yet another chart I found on the interwebs, (I love charts) and found out that the port is .003" larger than the maximum recommended. In spec would be between .070" and .086". So, yeah, it must be over gassed, right?.....

Even if it was slightly overgassed, wouldn't the extra mass of the FA BCG mitigate that? Then there is this. The spent brass has tiny little dings in the center. Just where you would expect it to be if it hit the brass deflector. So, if the system is over gassed, how the heck is the brass hitting the deflector and putting the brass way out in front of me? I'm so confused.

With all that said, here are some of the solutions that have been suggested.

1) Get an adjustable gas block.
2) Stop shooting M855 and use M193 instead 'cause M855 is just too hot.
3) Get an adjustable gas key.
4) Get a longer buffer spring and start snipping away until brass lands at 3 o'clock.
5) Get a heavier buffer, but it wont fix the problem, it will only damage the rifle in the long run.
6) if it ain't broke, don't fix it.

Though there are varying degrees of work and expense associated with the suggested solutions, save for #6, I came up with my own extremely simple low cost solution. Just crimp the gas tube close to the gas block until the brass lands where it should. It is not likely to be dangerous and if I mess it up, it is easily reset with a new $10.00 gas tube.

The only problem I see with my solution, or the others, is that nagging question about brass hitting the deflector. Could it be that the system is under gassed and brass is bouncing forward off the deflector.? I would not think so but the dings consistent with brass bouncing off the deflector are there.

It just don't add up and my OCD is in overdrive. What I know for sure is this. The gas port is out of max spec by +.003", the spent brass has tiny dings, brass is landing at 1 o'clock, and I need help.
 

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Scorpio, Not being an AR-15 expert, I think #6 from your list would be the most appropriate ... if it ain't broke, don't fix it. Because all parts are related to the total timing sequence of events, if you change one to accommodate a different result, you could end up reducing reliability.

In a DI AR-15 system, gas pressure impinges on the bolt and drives it back to cycle the action. Increasing gas pressure just drives the bolt faster and makes spent cases eject farther. I hadn't considered the direction of ejection because it just doesn't matter ... unless spent cases are smacking you in the face.

Try the 10 buck gas tube experiment ... it will definitely affect gas pressure. If it doesn't work, you're not out much. If it does, you will have "braggin' rights" for a premature ejection fix.
 

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In all seriousness, OP, I understand where you're coming from. A semi auto pistol I owned used to deposit a nice little pile of brass right at about 3:00, and I always thought that was the the coolest thing. Trying to make a gun do that, though? Can drive you to the crazy house.
 

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Discussion Starter #5
Darn. Does someone have a teensy bit too much spare time on his hands? :)
Well, yeah, I guess. In about a month I'll be back to having no spare time at all again when I go back to working two jobs after landscaping season begins. Did I mention I have a touch of OCD? :D You don't want to see how I detail a car. :eek:

Iowegan,

Thanks for the input. I think the simplest solution will be to crimp the tube. If that does not work I may try the adjustable gas key just because it's something I've never messed with before.
 

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Evening Scorpio;

It does sound like you are slightly over-gassed OR not quite enough buffer spring tension.

It sounds like your spent brass is bouncing off the brass deflector with vigor so your bolt speed is up there pretty good.

Have you tried slightly lower power rounds yet? (like M-193 or over the counter .223)-- If that helps the ejection then you are definitely over-gassed.

My usual first thing to try is a slightly stronger buffer spring. I probably have 15 buffer springs hanging on my shop wall from different manufactures & they all have slightly different loads & rates.

If you have a different AR (or AR's) then maybe try the buffer spring from those guns in your problem gun.

I have a homemade spring tester but on the AR buffer springs I usually just slide the buffer spring on a tube or piece of pipe, then a washer, then the new (different spring). When I slide (compress) the springs together on the pipe the strongest spring will obviously compress less.

It is difficult to tell what a buffer spring will do (compress like) as sometimes the longer ones will have more coils therefore being a lower load & rate. Short & thicker wire will usually be stronger. Some springs that look almost identical will compress differently (so try some different springs)

Anyhow, my suggestion is to see how good you can get it with the ammo you intend to shoot the most by playing with buffer springs first. If that can't get you what you want then an adjustable gas block is a real nice tuning tool but those things can be a pain in the a$$.

Or, if you think your barrel gas hole is too large you can remove your gas block, then drill & tap the gas port hole, then install a set screw in that tapped hole, then drill a new gas passage hole to any size you want in that set screw.
 

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Discussion Starter #8
Evening Scorpio;

It does sound like you are slightly over-gassed OR not quite enough buffer spring tension.
With the gas port over sized by +.003 out of max spec, I'm going to go with over gassed. I think before I start crimping the gas tube, I'll put a couple boxes of 55gr .223 through it just to prove the theory before I start making mods.

I really want this rifle to work well with M855 since that's the ammo I use in my SPR as range fodder.
 

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I have a 16" mid length and I prefer heavier buffers. I use a 6.5 oz. buffer in mine. In my 18" with a rifle length gas system, I use an M16 BCG and a 5.6 oz. buffer. The M16 BCG is .4 oz. heavier than a typical AR BCG. Ejection with mine is in the 4:00 area.
 

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Interested to hear how it does with the M-193 ammo. I don't know anything & have nothing to offer but my curiosity is up lol.
 

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Discussion Starter #12
I have a 16" mid length and I prefer heavier buffers. I use a 6.5 oz. buffer in mine. In my 18" with a rifle length gas system, I use an M16 BCG and a 5.6 oz. buffer. The M16 BCG is .4 oz. heavier than a typical AR BCG. Ejection with mine is in the 4:00 area.
I think in the circumstance with the carbine gas system and the over sized gas port, any benefit I get from the M-16 BCG is negated. My first reaction was to go with a heavier buffer but was told the it may put more stress on my rifle. I also have an SPR with a middy gas system that I run with a FA M-16 BCG and it ejects at 3 o'clock. the barrel is a Rainier match so the tolerances are probably stricter. That was my first build, if only they were all that easy.

Stuff like this..........is why I love bolt action rifles and single action revolvers more and more:)
I am a big fan of simplicity. When I worked for Bell Labs I was told by a real engineer that the less moving parts a system has, the more reliable it will be. But I'm also kind of a nerdy engineer wannabe. Problems like the ejection pattern issue are just another fun puzzle to solve.
 

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I'm about to just get a .223 Handi Rifle for range shooting, it's basically a stocked zip gun:)

In all seriousness I know what you mean, I used to get obsessive about my wheelguns, if the carryup was 1/16" more "sluggish" on one chamber of one of my GP100's it would keep me up at night......I also would obsessively change springs or shim them to try to get them "just right" and I have several that are as close to "just right"as a Ruger DA can get without expensive action jobs......now I just shoot them, as long as they work I don't worry about it.

If you want to get into amateur engineering, get into some of the German made guns, Germans live to over-engineer things and use 10 parts to do the job of 2, really fun to work on stuff like Mauser G43's, etc.
 
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