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Posted: 4/28/2005 9:39:44 PM EDT
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My rifle (RRA everything with an Armalite midlegnth barrel) has been short stroking and i've isolated the problem to the gas system. I've ruled out gas key problems and i think it may be an issue with either the gas block or the gas port on the barrel. Realligning the gas block has no effect. The rifle just isn't chucking the spent casings like it should. It's lazily dropping them out on my arm and getting a stovepipe every 5 rounds or so. Suggestions? |
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As i said, i ruled out any other problems. It is a problem with the gas system. I've put other uppers on the gun and they work fine. The problem isn't the system moving to fast, the problem is the system moving too slow. It's not throwing the shells clear. Every other AR i've used throws the shells a good distance, this one is dropping them on my arm when it's not stovepiping. |
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1. Shoot with one round in the magazine and note if the bolt locks back properly. If it does, then you are getting enough gas. 2. If #1 indicates not enough gas, check the gas system for clogs and the gas tube and carrier key for proper fit. Hand cycle the bolt and make sure nothing is hanging up. If you are using an H buffer or anything wierd, go back to all stock. 3. If #1 indicates enough gas (bolt locks back), rebuild the ejector in your bolt. |
It's possible for it to be too fast, but doubtful in this case. When it cycles too fast, the pressure is still too high in the chamber and most of the energy is being used to yank the spent brass out. A heavy buffer is used to slow the action down and allow chamber pressures to drop. But if this were happening in your case, you'd probably have torn case rims from the extractor have to pull extra hard. Like Zak-Smith mentioned above, if it locks back on an empty mag after firing a single round, then your gas system is fine. Have you checked the ejector tension? Some people cut a few coils off the ejector spring to get their empty brass to land right next to them. A weak ejector spring would mimic this, and more so (like the situation you're experiencing.) |
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I put someone elses upper on my gun and all was functioning properly. I put my bolt in someone elses gun and it functioned properly. I even too the bolt out of a properly functioning gun and put it in mine and mine was still messing up. The bolt will lock back on the last round, |
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Check that chamber again. Should be smooth. Sometimes if the chamber reamer is worn it will make for a rough chamber or have concentric rings. If that ain't it, and your bolt flings the brass good in another upper, try the whole Bolt Carrier Group in that other upper. How did you index the gas port/gas tube/gas block? I take a paper clip and bend up about 1/8" and measure the distance from the back of the gas port to the back of the gas block/front site base. Check that against the distance from the shoulder on the barrel to the gas port. Edited to add: Is that the barrel you got from me? |
+1 |
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There's nothing magical. It's a fairly simple mechanical device, and you can narrow down the problem areas, like you've started to do with trying the bolt in another gun. Things to check: buffer, op spring, entire bolt carrier operation, any hang-ups when cycle gun manually, etc. |
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I have shot the gun in these configurations with these results. -All my parts: occasional stovepiping, not throwing rounds clear -my gun with someone elses bolt: occasional stovepiping, not throwing rounds clear -my lower with someone elses upper: Works fine. -My bolt carrier in someone elses gun: Works fine. Everything fits correctly and operates smoothly. From this information i hypothesize that it is not the lower not any parts in the lower, including the buffer and buffer spring causing the problem. As for the bolt/carrier, i don't see how it could be that either. |
| I had the same problem in a new build i had this past weekend. I didn't know what to think but i dropped a few drops of CLP on the walls of the upper and it ran fine. When i returned home i took the gun apart and found out the inside walls up the upper were a little rough and i took some fine steel wool and smoothed it down a bit. And a little more CLP it runs fine now. |
| Take a close look at the belled portion of the gas tube where it enters the gas key; if it's worn you will get major gas leaks and poor function. The bell should have the same OD as the main part of the gas tube and be even all the way around. A worn tube will cause exactly the problems you're seeing. The other possibility is that the gas port is too small and/or is restricted by an internal burr. I had a barrel from a major maker that wasn't drilled completely through; once dirlled out it worked well. |
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I tell you this sounds like a over fuction. Check your brass for heavy extraction marks, if you have real heavy marks then the system is over fuctioning/moving to fast and the lock up is waiting to long to release after the pressure drops to unlock. This will throw your brass just outside the upper. I had the same problem a few weeks back. The gas hole on the barrel was to large. I changed barrels and no more problems. |
Already checked.
Ugh, that would suck, too big is a lot worse than too small. Too small can me widened. How do i check that? |
Check your brass. Look for signs of stress on the fired rims. You can slow it down by using a heavier buffer and you can also use a FA carrier which has more mass. Mine was so bad nothing worked. So I ended up replacing the barrel. If you want to check the barrel, take the tower off and mike the gas hole. |
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You shouldn't have to go through all this bull shit to get it to run. Did you check that chamber yet? That was a brand new barrel from ArmaLite. I bought it like last fall just before Giffman started his group purchase. Let me know if you want me to start the process. IM incoming. |
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That would be a start. Blow some air down the gas tube and see if you have good flow through the tube and out the gas block. Check the gas port in the barrel while you have it off. Also check the port in the gas block. If you can, try and check to make sure the hole in the gas tube lines up with the hole in the gas block. Kind of eye ball how far up the gas tube is from the inside top of the gas block. Bend up an end of a paper clip and see if you can fit it up through the port in the gas block up into the gas tube. If it won't go drive the roll pin out and check the indexing of the tube to the block. Edited to add: You probably already know this but the hole in the barrel, the hole in the gas block and the hole in the gas tube all have to line up. If that is happening everything should be good to go. Also use that paper clip to measure the distance from the back of the block to the gas port in the block. That should be the same distance from the shoulder on the barrel that locates the block to the port in the barrel. |
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You mentioned that you had the Wolff spring in there... is there any chance that it's too tight on the buffer and hanging up on it? When I put the heavy 9mm buffer in my Bushmaster it was causing me all kinds of grief until I opened the diameter of the spring up a bit by twisting it. When I hand-cycled the rifle it seemed fine... maybe a little more force to pull it back, but not much. However, when I was shooting it sometimes the buffer would hang up on the spring and not push the bolt carrier forward all the way. It would strip the round off the mag and it would be sitting loose in the chamber, but the bolt would be at least an inch or so from closing. Hitting the forward assist did absolutely nothing to move the BC, either... I had to pull the charging handle back to get it to move... Maybe yours is binding up on the way back and not allowing it to toss the brass out forcefully? You mentioned earlier that the bolt was locking back on the last round, so it's getting enough gas to cycle it (perhaps barely), but I'm just wondering if the spring is binding up on the buffer similarly to what mine was doing. Do you have the standard spring still so that you can change it out? Did you change the spring at the same time you put on the new barrel? If so, maybe it's not the barrel... |
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I did this at the range when it first started happening as i suspected the gas block. i sprayed some gun scrubber down the gas tube and it seemed to flow well. came right out the barrel. I'm not using the front handguard cap, i installed a FF railed forearm. I eyeballed it to line up the gas block. there's no finish where it was seated from the factory so i lined it up with that. We adjusted it a couple times at the range with no success. As far as the wolf spring goes, the gun worked flawlessly with someone elses upper, but, just incase, i'll bring the original spring with me to the range next time. I built the gun from scratch so there's no way of telling what part i put on that is causing the problem. I don't think the spring is binding because i've hand cycled the bolt hundreds of times and it's smooth as can be. |
| okay, I took a look at the gas ports and everything seems fine. I reinstalled it taking extra precautions to make sure everything was lined up perfectly. If that turns out to be it i'm NEVER buying a barrel without a pinned FSB ever again. I'm going to head out to the range next week with it, a spare completely stock lower, and a spare bolt/carrier. |
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one other thing not mentioned but has happened to me befor i had a oly m4 barrel it would lock up not eject sometimes it it would try to shove another round into the stuck case. turned out it has misalligned locking lugs i sent it to oly they had back to me in less than a week and it funtioned 100% from then on. |
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