AR9 troubleshooting

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A few months ago was asking questions about an AR9, an outstanding NES'r let me try a couple of his, started picking up parts and finally got to trying mine out today.

Is a Colt version, Spikes BCG, recievers, and 9mm buffer (the long one they make); BA 8 inch Barrel; Aero CH, rail, tube; JP polished spring; ALG ACT trigger; 4 inch KAW linear comp; and I stuck an SB brace on there. Running it on metalform 32 rnd mags.

In putting it together I ran into a problem where the ejector, not the tip just the top edge of it back near the bend, was hanging up the BCG. I got in touch w/ spikes and they indicated this is something that occurs and I should remove a little material - I did and insant joy.

I gave it a sanity headspace check, basically verified a no go gauge holds the bolt a little open and a go gauge isn't sloppy. Cleaned and lubed it up like any other AR and off I went..

It ran about 110 rounds today on federal FMJ 124 grain without failure (then kinda went bezerk and will get into that momentarily). My initial impression was I feel like the buffer is bottoming out in the tube, like maybe it wants a stiffer spring or a regular AR buffer to allow it more travel.

After about 110 rounds I got a stovepipe, followed a few shots later by a double feed, blamed it on a bad mag maybe (started with 4 loaded and was on the 4th at the time).. Loaded up another mag and got all types of malfunctions, stuff I don't have a name for including a sideways (vertical way) feed...

Obviously a cleaning and re-test is in order but I see nothing wrong mechanically here, is just how it started with a little residue mixed in. I do have a heavy spring here to try too.

Is there a special way to load colt AR9 mags? They do seem goofy to me, almost want to kinda spray rounds out or let the top one pop up, which could be totally negligent loading.

Any ideas of what else I ought to be chasing? Thx in advance!

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Not an AR guru by any means, but until they get up here's my two cents. Mags are usually the first thing most of us would suspect, but one that functioned earlier did not change the issue. Ammo worked, so no issue, unless some different rounds got mixed in. Something may have loosened up in test firing. It's your rifle, you assembled it, so you've got the best feel for what went into it, and probably already have the answer. If you suspect an issue with the buffer or recoil spring, check them. Look at your spent brass for marks/damage you wouldn't ordinarily see. Anything unusual about the distance it flew, or anything to indicate weak/strong functioning? Parts from different manufacturers don't always mesh well, and a part can go bad. Disassemble and check. Sometimes I just forget to tighten things, but that's only me. Good luck.
 
Which JP polished spring is that? I think you want the 308 power spring for 9mm blowback, as well as the matching length of your buffer tube. You most likely already figured that out, but something to mention just in case.
 
Which JP polished spring is that? I think you want the 308 power spring for 9mm blowback, as well as the matching length of your buffer tube. You most likely already figured that out, but something to mention just in case.

Its the carbine AR15 spring, picked it trying to match the Spikes spring they normally use that wasn't available at the time I was thinking about springs, basically from what I can tell Spikes just uses a quality standard power carbine spring so I did the same.

The pistol tube is an Aero really chosen because I had one hanging around, but they are the same as a carbine tube as far as I know and standard for 9mm AR's.

Will go back here and see about getting a Spikes spring at least on order. I do have a Wolf heavy AR15 carbine and a couple types of AR10/DPMS carbine springs here I could also try (an Aero & Sprinco orange).

I do suspect something isn't right there, system sanity checks as far as BCG allowable travel but the short stroking is ending abruptly with the bumper hitting the end of the tube I think. I am not totally clear on why we want the short stroking either, makes the whole spring combo very critical as the travel is reduced.
 
Its the carbine AR15 spring, picked it trying to match the Spikes spring they normally use that wasn't available at the time I was thinking about springs, basically from what I can tell Spikes just uses a quality standard power carbine spring so I did the same.

The pistol tube is an Aero really chosen because I had one hanging around, but they are the same as a carbine tube as far as I know and standard for 9mm AR's.

Will go back here and see about getting a Spikes spring at least on order. I do have a Wolf heavy AR15 carbine and a couple types of AR10/DPMS carbine springs here I could also try (an Aero & Sprinco orange).

I do suspect something isn't right there, system sanity checks as far as BCG allowable travel but the short stroking is ending abruptly with the bumper hitting the end of the tube I think. I am not totally clear on why we want the short stroking either, makes the whole spring combo very critical as the travel is reduced.

Because there's no gas system, AR9 direct blowback is actually a lot more bolt force than an AR15 and often requires a heavier spring for proper timing (depending on bolt/buffer weights of set up and loads shot). You might actually have some better results with an AR10 spring if you think you're currently bottoming out. If it's smashing against the end of the buffer tube, then it's bouncing back faster than normal and could be causing your stovepipes and feeding issues.
 
Because there's no gas system, AR9 direct blowback is actually a lot more bolt force than an AR15 and often requires a heavier spring for proper timing (depending on bolt/buffer weights of set up and loads shot). You might actually have some better results with an AR10 spring if you think you're currently bottoming out. If it's smashing against the end of the buffer tube, then it's bouncing back faster than normal and could be causing your stovepipes and feeding issues.

Thanks, I had the thought that maybe after 100 rounds of break in things were running smoother and made that problem worse...

What is odd though to me though with short stroking and blowback is it seems like you'd want a nice long controlled sweep with room to take up error, ie slightly hotter round and the BCG goes a little further, underpowered round and it doesn't go as far but is still able to eject and pickup a new round, spring smoothing the system out versus a short throw that provides less room for error.

Obviously I don't quite get it but does seem to be something wrong spring wise and that is the only piece of the formula I didn't get from Spikes (unless their pistol tubes are longer, which just doesn't make sense if so as that is AR15 spec stuff).
 
Thanks, I had the thought that maybe after 100 rounds of break in things were running smoother and made that problem worse...

What is odd though to me though with short stroking and blowback is it seems like you'd want a nice long controlled sweep with room to take up error, ie slightly hotter round and the BCG goes a little further, underpowered round and it doesn't go as far but is still able to eject and pickup a new round, spring smoothing the system out versus a short throw that provides less room for error.

Obviously I don't quite get it but does seem to be something wrong spring wise and that is the only piece of the formula I didn't get from Spikes (unless their pistol tubes are longer, which just doesn't make sense if so as that is AR15 spec stuff).
Definitely a heavier spring. The ones you will buy will often say 9mm/308 on them. Do not use the standard AR15 carbine spring. I also assume you have a spacer or a longer buffer. Also the buffer weight should be up in the 5.5-10oz range. Angstadt has a buffer kit that is a stiff spring, spacer and 5.7 or 5.8oz buffer. Others make similar setups. I like the longer buffer so you do not need a spacer
 
Thanks, I had the thought that maybe after 100 rounds of break in things were running smoother and made that problem worse...

What is odd though to me though with short stroking and blowback is it seems like you'd want a nice long controlled sweep with room to take up error, ie slightly hotter round and the BCG goes a little further, underpowered round and it doesn't go as far but is still able to eject and pickup a new round, spring smoothing the system out versus a short throw that provides less room for error.

Obviously I don't quite get it but does seem to be something wrong spring wise and that is the only piece of the formula I didn't get from Spikes (unless their pistol tubes are longer, which just doesn't make sense if so as that is AR15 spec stuff).

In theory, the AR10 spring will still get the majority of travel, even though it is stiffer. That's just how violent direct blowback is. Using a standard strength AR15 spring on a AR9 blowback system could provide no effective deceleration if it is bouncing. AR10 spring will give the proper deceleration and return the bolt before the bounce (again, theoretically). So it's less about total traveled distance and more about proper deceleration of the bolt. The only catch (literally) with the heavier spring is that you need to ensure proper bolt catch clearance if you want LRBHO to still work.
 
I use a JP extra power AR15 buffer spring in my AR9 SBR. I found the AR10 spring was too heavy for my 147 gr loads. Had lots of FTE's. Once I switched to the extra power AR15 spring, the FTE's disappeared...for the most part.

I get an occasional FTE which I think is an issue with the Stern Defense ejector (using an adapter in AR15 lower).

Anyway, I'd also look at the ejector and/or the extractor.
 
Definitely a heavier spring. The ones you will buy will often say 9mm/308 on them. Do not use the standard AR15 carbine spring. I also assume you have a spacer or a longer buffer. Also the buffer weight should be up in the 5.5-10oz range. Angstadt has a buffer kit that is a stiff spring, spacer and 5.7 or 5.8oz buffer. Others make similar setups. I like the longer buffer so you do not need a spacer

I'm using the Spikes long buffer that is for 9mm and is a 7.7 ounce.


Also have a spacer hanging around I could use w/ a standard buffer.
 
Although the spring sounds like a candidate for examination, I would think that would make itself known immediately, not after almost 4 error-free magazines. I mean, what changed with the spring after 4 mags?

If you think the buffer is bottoming out, you might try pulling the buffer and looking over the polymer end. Is it mangled? If it's bottoming out, you should see some impact indications.

Colt mags are "standard" double-stack magazines, and load by pressing straight down, just like an AR mag.

When in the cycle are your malfunctions occurring? I ask because it's possible you developed an extractor or possibly an ejector issue. I'd pull the bolt and give it a good eyeball, and look at the ejector, especially since you did some work on it.

Keep in mind these errors didn't start until after 100+ rounds. A spring issue would have made itself known immediately.
 
I use a JP extra power AR15 buffer spring in my AR9 SBR. I found the AR10 spring was too heavy for my 147 gr loads. Had lots of FTE's. Once I switched to the extra power AR15 spring, the FTE's disappeared...for the most part.

I get an occasional FTE which I think is an issue with the Stern Defense ejector (using an adapter in AR15 lower).

Anyway, I'd also look at the ejector and/or the extractor.

Ejector and extractor look like they did originally, seem ok, the JP spring I'm using might be that exact spring but I know it as something that works well in any standard AR15 carbine tube, and better with an H2 even, nice quiet springs.
 
Ejector and extractor look like they did originally, seem ok, the JP spring I'm using might be that exact spring but I know it as something that works well in any standard AR15 carbine tube, and better with an H2 even, nice quiet springs.
Do you have another bolt you can swap in to check? If not, come get one from me if you want to do some more trouble-shooting.
 
Although the spring sounds like a candidate for examination, I would think that would make itself known immediately, not after almost 4 error-free magazines. I mean, what changed with the spring after 4 mags?

If you think the buffer is bottoming out, you might try pulling the buffer and looking over the polymer end. Is it mangled? If it's bottoming out, you should see some impact indications.

Colt mags are "standard" double-stack magazines, and load by pressing straight down, just like an AR mag.

When in the cycle are your malfunctions occurring? I ask because it's possible you developed an extractor or possibly an ejector issue. I'd pull the bolt and give it a good eyeball, and look at the ejector, especially since you did some work on it.

Keep in mind these errors didn't start until after 100+ rounds. A spring issue would have made itself known immediately.

Was hoping the buffer would be mangled or the spring would be in pieces - "aha!" :).. no such joy :(..

Extractor, ejector, everything looks tip top, nothing wierd in the upper or BCG for marks, will re-examine extractor as the look is a little subjective.

I believe the malfunctions occur about when the bolt is back to eject - like the ejector isn't quite right or the extractor won't let go, but that doesn't explain the double feed, sideways feed, or 100 rounds then failures starting unless I can identify something broke. Almost wonder if hammering from the wrong spring makes the mag expel rounds on its own and gums up the works?
 
Do you have another bolt you can swap in to check? If not, come get one from me if you want to do some more trouble-shooting.

Ya that would be sweet, being my first I don't have a cache of parts, yet :)..

Also not familiar with what looks right and doesn't but mine doesn't run as smooth recoil wise as yours, very distinct hard wallop I believe is that buffer bottoming out.

Will get you on IM thanks!
 
Definitely get yourself an AR10 / 308 carbine spring from a reputable manufacturer.

You can experiment with lighter buffer, but what you have is pretty much ideal: a bolt and buffer that total about 18-20oz.

The only real reason to NOT short stroke is if your magazine springs are weak, but your new metalform mags should be GTG.

Stovepipe malfunction can be caused by a weak extractor. Check yours by removing the bolt, hooking a round under the extractor on the bolt face. It should hold the round wile you lightly shake around of the bolt. If the round falls away easily contact the bolt manufacturer
 
I still haven't heard anyone clamoring for a new/stronger recoil spring explain why the gun ran flawlessly for 100+ rounds before it started burping.

I'm running standard AR15 carbine springs in both my 9mm ARs behind Spike's ST-9X buffers and they run like sewing machines.

I'll be interested in the results when he gets a chance to swap bolts. A factory 9mm AR (his is practically a factory Spike's gun) shouldn't be this finicky.
 
I still haven't heard anyone clamoring for a new/stronger recoil spring explain why the gun ran flawlessly for 100+ rounds before it started burping.

I'm running standard AR15 carbine springs in both my 9mm ARs behind Spike's ST-9X buffers and they run like sewing machines.

I'll be interested in the results when he gets a chance to swap bolts. A factory 9mm AR (his is practically a factory Spike's gun) shouldn't be this finicky.

It's possible that a brand new AR15 spring would allow for temporary use until it is broken in, then didn't provide enough force reduction to cycle properly from there.

AR15 springs can potentially work depending on your set up (reciprocating mass being a key factor), but most will not recommend it for blowback, particularly because OP notes bottoming out.
 
It's possible that a brand new AR15 spring would allow for temporary use until it is broken in, then didn't provide enough force reduction to cycle properly from there.

AR15 springs can potentially work depending on your set up (reciprocating mass being a key factor), but most will not recommend it for blowback, particularly because OP notes bottoming out.
I'd be awful surprised if a new AR spring would "break in" in just 100 rounds, tho. When he pulled it out, it was "regular" size, no breaks, etc. And, to be honest, OP thinks it might be bottoming out. He's not sure.

One thing I didn't do when he was here yesterday was measure his pistol receiver extension (buffer tube) . I assume they're the standard carbine length, but I've never measured one (I run "carbine" receiver extensions , as my ARs are SBRs).

BTW, I have literally thousands of rounds through my 9mm ARs, suppressed and unsuppresed. The AR15 springs "potentially" seem to work just fine.
 
I'd be awful surprised if a new AR spring would "break in" in just 100 rounds, tho. When he pulled it out, it was "regular" size, no breaks, etc. And, to be honest, OP thinks it might be bottoming out. He's not sure.

One thing I didn't do when he was here yesterday was measure his pistol receiver extension (buffer tube) . I assume they're the standard carbine length, but I've never measured one (I run "carbine" receiver extensions , as my ARs are SBRs).

BTW, I have literally thousands of rounds through my 9mm ARs, suppressed and unsuppresed. The AR15 springs "potentially" seem to work just fine.

Under direct impingement or piston, I would be surprised too. Under 9mm blowback compression slamming off the end of a buffer tube? Possible.
 
I measured the tube and came up with 7.25, so all indications are its a carbine tube.

Just played with the extractor, you really can't shake a round out without a real hard shock. Round pops right out with correct pressure applied but it can support the weight of the BCG easily as pictured.

I believe the stovepipe may have been speed, round bouncing back in (based on totally unrelated maybe but AR10 over gassed "features")..? or maybe that extractor isn't losing its grip because it works too well ?..

I will go out back a little later and try a hand cycle of a mag, not sure what to expect from an AR9 for ejection since it lacks a spring loaded ejector but might show something?

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I pulled the firing pin and cycled a few mags by hand (just can't get to shooting until the weekend where I will re-test)..

First go at it, ejector/extractor was working tip top but the slow way I was manipulating the bolt resulted in a double feed.

After that I let the bolt slam shut every time and there was consistent ejection and pattern.

Playing around with my mags, a few of them, after the fact - they are loading easier now, getting broken in a little, but I notice something very similar to my Sig 20 round 9mm models: if I manually eject a round by hand, you can cause a chain reaction and trick them into spraying a bunch of rounds out. This is the situation I ran into in my first manual test that caused a double feed and something I believe I saw some in the live testing. Normally the bolt is there and everything happens so fast only 1 round can pop up and that spraying (puking if you will) chain reaction cant get going but if the bolt returns slowly somehow such can happen w/ a double feed.

I will always be sure to let the bolt slam shut initially now in testing. I think I may have occasionally been watching it chamber and using the charging handle to slow it down when initially chambering rounds in testing.

If my mags are wonky they all work the same, so I think this artifact I am uncovering with puking is not an actual problem.
 
Thinking about this a little more, a double feed may point to spring as well, ie not closing the bolt with the speed and force to prevent mag puke.
 
I got it out today for real testing, with 2 spare BCG's.

With the spring change the bottoming out feeling is gone.

All 3 BCG's, 5 mags, both a Wolf heavy made for colt 9mm AR's and a stock Spikes spring (the one they ship w/ their AR9) all were consistently having frequent failure to eject (extract OK). What happens usually is the empty round ends up above the new one and it jams that way, with occasional stove pipes or the empty round gets vertical in there somehow..

One odd detail is usually this seems to prevent me from putting the safety on (ie when I go to clear it), initially was thinking maybe short stroking, but that might just be a function of the BCG position putting pressure on the parts - will play with it later to see how that works.

Pictures - empty round and a new one involved in each failure.


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