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Posted: 1/28/2013 12:40:22 PM EDT
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I didn't want to be the noob coming on asking the same question that's been asked 100 times, but after a couple hours of research I can't find anything that sounds to match my problem exactly.
I just finished my first build which is also my first AR. I built the lower, but chose to buy a complete upper. Before I test fired it, I took the bolt apart to examine, clean and oil everything. I got about 10 rounds through it and had a failure to eject. New round and spent cartridge are jammed in one on top of the other. Dropped the mag and they both fell out, popped the mag back in, pulled the charging handle to chamber a new round and it cycled fine for about 6-8 rounds and the problem repeated and continues to repeat every 6-8 rounds. I tried 3 different ammos, some brass Prvi, some brass Remington, and some steel Wolf(I know, I know). Both of the brass had the same problem, however the steel ejects fine yet fails to feed a new round at all. I have tried 4 different mags. They are all the same, but they are also all I have. Can't exactly go my local gun shop and pick up a pmag to try right now. I'd tinker with it and fire away until I get to the bottom of it, but I can't exactly replenish my ammo supply right now either. Need some help before I'm stuck with no ammo AND a gun that don't work. |
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Sounds like short recoil due to a combination of a new gun that needs break-in and underpowered ammo.
The milspec finish of most ARs causes a lot of friction until it wears down/breaks in, and you can't tell if you have a hardware problem until you get it broken in. Clean the gun and remove all of the lubricant, then dry cycle the gun using the charging handle 100-200 times, then clean to remove wear particles, and lubricate normally. Take it out and shoot the gun 300-500 rounds with full power ammo like Lake City/Federal M193 or M855. After that, if you still have a function problem, then, there's a problem. |
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At face value of the info it sounds like it is short stroking, meaning that the round fires, the bolt unlocks and extracts the empty case, but doesn't go back enough to eject the empty case, then the bolt carrier assembly goes forward and pushes a live round off of the magazine while an empty case is still present, causing a jamb. Start with a thorough cleaning on the chamber, and make sure you remove any solvent or oils so it doesn't cause casings to stock. Next lubricate the 7-bolt lugs and the entire bolt carrier so it is glissening wet like a glazed donut. If the bolt rotates very stiffly in and out of the bolt carrier, try adding a drop or two of lube to the gas rings, and make sure the gas key is fastened tight to the bolt carrier and properly staked. Then try to shoot it again and see what happens.
If you could help with a little more info on the complete build, it might help provide some more insight as to what other things to look at. On the upper, who built it, length of barrel and gas tube length, does it have a gas block or pinned front sight base, type of bolt carrier (semi or auto)? On the lower, which stock, buffer, and buffer spring are being used? When you disassembled the bolt carrier assembly, did you remove the extractor, and if so then did you notice what color of extractor spring & extractor spring insert that it has (along with any O-ring or D-ring present)? CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
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I'm no expert but....... It sounds like it may be short stroking. A fairly easy way to check for this is to load only one round in the mag, charge the gun and fire the round. If the gun is short stroking the bolt will not lock open. If your gun fails every 8 rounds or so, you may have to repeat this test several times to catch it doing it. If the bolt fails to lock open on an empty mag, it is likely short stroking. Short stroking is often caused by low pressure which could be caused by light loads, loose gas key on the carrier, crimped gas tube, improperly installed gas tube, rifle length gas system on a short barrel, or possible a combination of any of these. I could be wrong but it is something to consider. Also, low pressure is not the only cause of short stroking. Like I said, I'm no expert and this is just my guess/opinion. |
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Quoted:
The milspec finish of most ARs causes a lot of friction until it wears down/breaks in, and you can't tell if you have a hardware problem until you get it broken in. Clean the gun and remove all of the lubricant, then dry cycle the gun using the charging handle 100-200 times, then clean to remove wear particles, and lubricate normally. It's always the simplest stuff you don't think about when you are inexperienced. I wouldn't have thought to do that. I've lubed the piss out of it since day 1. |
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Quoted:
At face value of the info it sounds like it is short stroking, meaning that the round fires, the bolt unlocks and extracts the empty case, but doesn't go back enough to eject the empty case, then the bolt carrier assembly goes forward and pushes a live round off of the magazine while an empty case is still present, causing a jamb. Start with a thorough cleaning on the chamber, and make sure you remove any solvent or oils so it doesn't cause casings to stock. Next lubricate the 7-bolt lugs and the entire bolt carrier so it is glissening wet like a glazed donut. If the bolt rotates very stiffly in and out of the bolt carrier, try adding a drop or two of lube to the gas rings, and make sure the gas key is fastened tight to the bolt carrier and properly staked. Then try to shoot it again and see what happens. If you could help with a little more info on the complete build, it might help provide some more insight as to what other things to look at. On the upper, who built it, length of barrel and gas tube length, does it have a gas block or pinned front sight base, type of bolt carrier (semi or auto)? On the lower, which stock, buffer, and buffer spring are being used? When you disassembled the bolt carrier assembly, did you remove the extractor, and if so then did you notice what color of extractor spring & extractor spring insert that it has (along with any O-ring or D-ring present)? CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 Surplus Arms lower with DPMS parts kit. SOTA carbine upper with 16" barrel and quad rail gas block. Semi BCG, not chrome. ATI stock with hybrid buffer. http://www.atigunstocks.com/stocks/140-ar-15-stikeforce-stock-with-aluminum-hybrid-buffer-tube.html Extractor has a black insert, no donut. I ordered some heavier springs with donuts from Larue, then realized I don't have an extraction problem. At least I'll have spares. |
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Quoted:
I'm no expert but....... It sounds like it may be short stroking. A fairly easy way to check for this is to load only one round in the mag, charge the gun and fire the round. If the gun is short stroking the bolt will not lock open. It has not failed to lock open, but I may not have repeated the test enough to completely eliminate the possibility. Quoted:If your gun fails every 8 rounds or so, you may have to repeat this test several times to catch it doing it. If the bolt fails to lock open on an empty mag, it is likely short stroking. Short stroking is often caused by low pressure which could be caused by light loads, loose gas key on the carrier, crimped gas tube, improperly installed gas tube, rifle length gas system on a short barrel, or possible a combination of any of these.
I have thoroughly checked and double checked the gas system. There is no visible damage to the tube, block appears to be properly aligned and the key is tight like a tiger. Quoted:I could be wrong but it is something to consider. Also, low pressure is not the only cause of short stroking.
Like I said, I'm no expert and this is just my guess/opinion. Expert is a relative term. People like me make people like you appear to be experts. |
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It was a fairly low budget build. I didn't buy the cheapest junk I could get my hands on. I might be a little bias, but I think it's fairly well put together. It was supposed to be a learning experience and the first of many to come, but due to the political climate I guess we will see about that.
I really appreciate all of the input, apparently I've come to the right place for AR knowledge. I hope that some of the simpler solutions here will remedy the problem. I probably won't get a chance to shoot again until this weekend, In the mean time, any other suggestions are welcomed. Even if it;s not my problem, I'm loving all the info I'm getting. It may prove very valuable in the future. |
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What magazines, what buffer? Did it do this with more than one different magazine? I have several magazines, but they are all the same. AR Stoner (the only thing I could get at the time). I tried 3 or 4 of them to see if maybe I had a bad one. My brother grabbed a few P mags, so I'm going to see if I can throw one of those in there next time I try it. I was wrapping up my build right about the time the panic went full pop, I grabbed the only mags I could get my hands on. |
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So I got it back to the range today. Got about 20 rounds through it without a problem, then failed to feed again. After 20 rounds, it would only fire 1 at a time for the rest of the trip. I can load a mag, pull the charging handle, fire, extract & eject flawlessly. It just won't pick up a new round. No jams, just like the bolt never even touches the next round in the mag. Pull the charging handle and it feeds the next round fine. I played around with some loaded mags, empty mags and spent cartridges to see if it could be a short stroke problem. At the point where the spent casing is ejected, the bolt is not back far enough to pick up a new round. If pull the handle far enough even to eject an unfired round, it's still not back far enough to pick up the next round, but it is far enough to lock the bolt open on an empty mag. Before, I didn't think it was a short stroke because the bolt would lock open on an empty mag. Now I know that the bolt can open far enough to lock but fall just shy of grabbing that next round. I do have some carbon around the gas tube where it enters the gas block, I don't know if this is normal, because I've never had another AR to compare it to.
I've now fired 5 different brands of ammo, and 3 different mags. All yield the same result. My brother was having trouble wit his bolt not going all the way forward, so we put my bolt in his gun and it worked flawlessly, so I know that my BCG is fine. Unfortunately his Spike's BCG is jacked up, but at least he knows what's wrong with his now. Also put my upper on his lower to see if the different buffer setup made any difference, it did not. If anyone has any other suggestions, I would greatly appreciate it. I really don't want to send this thing back, the way things are right now it would likely be a good long while before I see it again. |
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Quoted:
Did you remove the lube and dry cycle the upper like I suggested? Yes. Quoted:
Did you shoot the gun with full power US made M193 or M855 like I suggested? I haven't been able to get my hands on any. I have M193 Prvi Partizan which is what I started with. Other than that, I've just been picking up what I can find when I can find it. Couple boxes of Remington Express rifle and some Walmart Winchester. Tried some Tul, but I should have know better. If ammo's the problem, I may have to wait until the panic subsides a bit before I can properly break it in. |
| Lube it until it bleeds, then every evening when you come in for a couple of weeks (since you'll be waiting on ammo anyway) pull the charging handle all the way back and let it go, don't ride it down. Do it 20-30 times. Clean it every few days. Just what was suggested above. This can really help on breaking in a new rifle when you're short on ammo. |
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Quoted:
Lube it until it bleeds, then every evening when you come in for a couple of weeks (since you'll be waiting on ammo anyway) pull the charging handle all the way back and let it go, don't ride it down. Do it 20-30 times. Clean it every few days. Just what was suggested above. This can really help on breaking in a new rifle when you're short on ammo. I'll do that. I'm not really short on ammo. Just apparently short on ammo that's good enough for my gun. My only question is, if this was strictly a break in issue, wouldn't the problem less frequent the more I cycle it, fire it, clean it and oil it? I had a couple of extraction problems the first time out, took care of that with new springs and inserts from Larue. The feed problem just seems to get worse rather than better. |
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20 rounds, then starts to have problems short stroking,
You have a gas leak somewhere that is happening when the steel parts heat up, Best guess, either a carrier key problem with a leak between it and the carrier, or you forget to loctite the gas block allen bolts, and the leak coming from there. Or you just using the wrong cleaning solvent and lube, and the chamber is fouling out quickly, and the problem at hand. Here, Hoppes solvent is not the right choice for the bore since it leaves behind a residue that quickly collets fouling. Instead, something like Sweets copper solvent works better since it removes copper a lot faster, and does not leave behind a residue. As for the rest of the rifle, CLP to both clean and lube it, including cleaning the chamber with a chamber brush and CLP by hand. If you need a source for CLP, then BreakfreeCLP in the large 16oz spray can is under $10 at wal-mart. |
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20 rounds, then starts to have problems short stroking, You have a gas leak somewhere that is happening when the steel parts heat up, Best guess, either a carrier key problem with a leak between it and the carrier, or you forget to loctite the gas block allen bolts, and the leak coming from there. Or you just using the wrong cleaning solvent and lube, and the chamber is fouling out quickly, and the problem at hand. Here, Hoppes solvent is not the right choice for the bore since it leaves behind a residue that quickly collets fouling. Instead, something like Sweets copper solvent works better since it removes copper a lot faster, and does not leave behind a residue. As for the rest of the rifle, CLP to both clean and lube it, including cleaning the chamber with a chamber brush and CLP by hand. If you need a source for CLP, then BreakfreeCLP in the large 16oz spray can is under $10 at wal-mart. I'll use the other cleaner as you suggested. I didn't assemble the bolt, SOTA did. The gas key is factory staked, I'd hate to go pulling it apart to see if that may be the problem and find out I did so for no reason. Especially since the bolt works just fine in another upper. Is there another way to check it without removing the key? Could I put compressed air to it and check for leaks that way? I loosened the gas block and slid it out of the way so that I could see the residue pattern around the gas port. It looks to be aligned properly and free of leaks. The only place I see anything I'm not sure about is on the gas tube at the rear of the gas block there is residue. I assumed this was normal, but again I don't really have the experience or other guns to compare it to. It's all cleaned up right now, but I'll go fire a few rounds and take some pictures to put up here as soon as I can. My word picture may not be as clear as an actual picture. |
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Just FYI, here are the parts I used.
complete upper: http://sotaarms.com/component/jshopping/product/view/2/3?Itemid=0 Stock, buffer and spring: http://www.atigunstocks.com/stocks/140-ar-15-stikeforce-stock-with-aluminum-hybrid-buffer-tube.html lower: http://www.surplusammo.com/saa-sa-15-grim-reaper-ar15-stripped-lower-receiver/ LPK: http://www.midwayusa.com/product/333717/del-ton-lower-receiver-parts-kit-ar-15 |
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ijasond,
Yes on using compressed air on the B/C to see if the carrier key is leaking against the carrier. Just hold the bolt in the inwards position, then pressure the key channel. Gas block allen screws have to be red loctited in place. If you need to remove the gas block later, then drop in a trash allen wrench into the allen bolts, the light up the allen bolt with a torch to transfer heat to the allen bolts to break the loctite bond to back out the allen bolts. Gas block to gas tube, should have light fouling, but if you have a major leak here, could be the problem at hand. Here, just use a cleaning jig with patch to semi close off the gas port within the barrel, the via piece of tubing, pressurize the gas tube from inside the receiver to check for leaks between the tube to gas block, and even gas block to the barrel. soap water works great to check for leaks, and if you have light leaks, your going to get bubbles. |
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ijasond, Yes on using compressed air on the B/C to see if the carrier key is leaking against the carrier. Just hold the bolt in the inwards position, then pressure the key channel. soap water works great to check for leaks, and if you have light leaks, your going to get bubbles. So, do you remember those bubble blowing lawn mowers they used to sell for little kids? Well, I have the AR15 equivalent, just apply soapy water and you have a bubble blowing gas key. This key is staked in, is staking these things a one time deal, do I need to just get a new one? |
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I removed the key. It was pretty snug, but not really tight and had no threadlocker on the bolts. Seemed to me like the bolts came out way too easy. I cleaned it and torqued it down real good, still leaked. It just didn't look like the surfaces were machined well enough to mate without leaking. I laid some 1000 grit sandpaper on a flat, smooth surface and worked the surface of the key flat(didn't take much), then again with 2000. Then I used a square key with a piece of 1000 grit paper on it (after also block sanding the key itself to make sure it was perfectly flat) to block the carrier surface. Then I cleaned it and torqued it all down again. Leak free! Pulled the bolts and threadlocked them in place. Looks like I might be good to go now. I really, really appreciate all the help. I never would have figured this out on my own.
I think I'll be reporting back with good news after the test fire. (knock on wood) |
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Not sure that I would have used the old key bolts since they may snap and make a mess of things, but you need to stake the key metal into the side spines of the bolt so they don't back out. The loctite is only used as a gasket between the key to carrier, and not to lock the bolts in place.
http://www.ar15.com/content/page.html?id=122 |
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Not sure that I would have used the old key bolts since they may snap and make a mess of things, but you need to stake the key metal into the side spines of the bolt so they don't back out. The loctite is only used as a gasket between the key to carrier, and not to lock the bolts in place. http://www.ar15.com/content/page.html?id=122 Thanks for the link, and all the advice. I got new bolts for the key and changed them out. Took it to the range and she ran flawlessly. Ate every ammo I had, including the Tul. Looks like you got it figured out for me. I'm really loving all the knowledge and people's willingness to help on this site. Hopefully before too long I'll be able to contribute myself. Thanks to everyone who provided information on this thread. I learned other things unrelated to this particular issue that I'm sure will prove invaluable in the future. |
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