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Posted: 5/24/2015 9:22:29 PM EDT
[#1]
Is the receiver extension straight, square and true on both of the new guns?
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Posted: 5/24/2015 9:35:27 PM EDT
[#2]
Headspace check ok? Chamber rough? Gas tube alignment ok with bolt carrier? Gas key screwed on to spec without leak or broken bolts?
Go over each part in a detailed inspection, you can find the issue. The faq in the build forum has good info too. |
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Posted: 5/24/2015 9:36:25 PM EDT
[#3]
When you say it is sticky feeling that tells me it might have alignment issues. The bolt should move freely by putting your pinky finger into the bolt and being able to move it in and out with very little resistance. It should be near liquid smooth but at the same time having new gas rings can cause it to be harder to move than normal. If you shot it the gas rings should allow free movement. If you cannot do this then it means there is an alignment issue. You can further test this by removing the bolt, charging handle, and simply putting the bare carrier into the upper. It should slide right out when you tilt it.
If you find it cannot slide out, then it probably means the carrier key is binding with the gas tube. You'll need to realign the gas tube. You may get away with a visual inspection and seeing if the gas tube is straight or not. It's quite alright if it wiggles a little and this should be normal. Plus did you test the gas tubes with a air can? And made sure you can feel air coming out from the gas tube when you plug the chamber? Just put cotton balls into the chamber and plug it up as best as you can and see if you can feel air coming out when you blow into the barrel from the front. I would say take it one step at a time. You already tested the bcg with another so you can narrow down your problem to something with the gas tube. From there it might be a problem with the buffer tube. Make sure when you close the upper that the bolt butt is touching the front part of the buffer. Plus on the cases that do fire, did you look at them? Make sure there isn't anything unusual with them? Like bent rims or torn out extractor marks? Blown out primers or really smashed primers like some fat person put his finger in a tub of fudge? |
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Posted: 5/24/2015 9:45:15 PM EDT
[#4]
So the bolt carrier from your working rifle made no difference, and things work relatively well when you cycle rounds manually. If you were just having problems with one new rifle you could blame it on tolerances etc. But two new rifles? That's got to be a bad batch of parts or improper assembly. Do you get good air volume when you blow through the gas tube with a straw?
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Posted: 5/24/2015 10:38:50 PM EDT
[#5]
Given the info you provided (and you're positive the gas blocks are properly aligned), it has to be either gas blocks that aren't completely machined or are obstructed or bad gas tubes. I would take the gas tubes off and make sure that air moves freely through them, then try a different gas block.
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Posted: 5/24/2015 10:40:07 PM EDT
[#6]
Don't know how to check it
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Posted: 5/24/2015 10:41:42 PM EDT
[#7]
All I could think to do to check the chamber was insert a fresh round and see if it came free easy - it did.
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Posted: 5/24/2015 10:49:52 PM EDT
[#8]
dalle0001 - The bolt carrier slide freely in the receiver, and the bolt seems to move with a resistance attributable to new gas rings. In any case, the BCG from the functioning unit did not help. As far as buffer, etc., I also swapped the whole lower - no change. I did blow thru the gas tube upon assembly and got what seemed to be expected flow. The tube seems free and straight, and when I removed the gas black to check alignment, the much larger hole in the gas block had left gas deposits around the barrel port that showed near-perfect placement.
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Posted: 5/24/2015 10:54:12 PM EDT
[#9]
wheel - having swapped the lower, my next thought was the gas system. I verified good tube/block alignment and SOME flow, but don't know how to measure it. I will try to compare it to the good unit.
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Posted: 5/24/2015 10:56:45 PM EDT
[#10]
ac130usnsr - the " I don't know how to do that" post was a reply to your question about receiver extension alignment - any suggestions? I am in the process of reviewing the build thread mentioned.
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Posted: 5/24/2015 10:57:14 PM EDT
[#11]
Quote HistoryQuoted:
Don't know how to check it Either take the gas tube and gas block off and try to blow air through them, or find a tube or small diameter straw that fits snug on the chamber end of the gas tube, plug the chamber of the barrel with a foam ear plug then blow air through the tube/straw while placing a finger in front of the barrel to feel for air flow. |
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Posted: 5/24/2015 11:00:48 PM EDT
[#12]
Quote HistoryQuoted:
ac130usnsr - the " I don't know how to do that" post was a reply to your question about receiver extension alignment - any suggestions? I am in the process of reviewing the build thread mentioned. Wasn't me, but if you can pull the charging handle all the way back with normal effort and don't feel any unusual resistance then it is fine. Given that you swapped out for your known good lower and still had the same issue, this wouldn't be the problem. Also, using your known good bolt carrier and still having the same issues means it's a gas problem. Since the gas ports on the problem uppers both gauge good, then it has to be misaligned or defective gas blocks or obstructed gas tubes. I would lean more towards misaligned or defective gas blocks. |
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Posted: 5/24/2015 11:08:19 PM EDT
[#13]
I was able to slip a short piece of hose over the end of the gas tube and blow thru it (by mouth) - both good and bad units seemed the same as far as resistance and flow.
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Posted: 5/24/2015 11:15:43 PM EDT
[#14]
I verified alignment of the gas block, and I can see both the gas block and the tube have relatively large ports (compared to the barrel) and I compared air flow thru the assembly in place with the good unit, so I don't see how that could be the problem. Still stumped.
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Posted: 5/24/2015 11:16:40 PM EDT
[#15]
Quote HistoryQuoted:
I was able to slip a short piece of hose over the end of the gas tube and blow thru it (by mouth) - both good and bad units seemed the same as far as resistance and flow. Only other things to try is to test the new bolt carrier groups in your known good setup. After that try to adjust the new gas blocks to get the most flow out of them. Other than that I would try new gas blocks/gas tubes. Still, based on everything you've provided, I would bet that the gas blocks were not perfectly aligned on the new uppers. |
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Posted: 5/24/2015 11:26:49 PM EDT
[#16]
dalle-0001 Just a clarification on the sticky BCG - the carrier slides freely in the receiver and the bolt seems to lock up freely, but sometimes it feels stuck when I try to retract it manually - I have to give a sharp tug or tap on the charging handle. I closely compared the lugs on the "good" and "bad" bolts, but can see no difference or damage. Can't easily see the mating surface on the barrel extension, but what I can see looks "normal".
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Posted: 5/24/2015 11:30:38 PM EDT
[#17]
Quote HistoryQuoted:
I verified alignment of the gas block, and I can see both the gas block and the tube have relatively large ports (compared to the barrel) and I compared air flow thru the assembly in place with the good unit, so I don't see how that could be the problem. Still stumped. Alignment comes in two parts. The alignment of the gas port then alignment into the upper into the carrier key. That can be off as well. |
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Posted: 5/24/2015 11:33:18 PM EDT
[#18]
ac130usnsr
As I mentioned elsewhere, when I removed the gas block after several malfunctions, the "donut ring" mark around the barrel port showed near-perfect concentricity and plenty of extra room for misalignment. Still think that may be the problem? |
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Posted: 5/24/2015 11:34:55 PM EDT
[#19]
Quote HistoryQuoted:
dalle0001 - The bolt carrier slide freely in the receiver, and the bolt seems to move with a resistance attributable to new gas rings. In any case, the BCG from the functioning unit did not help. As far as buffer, etc., I also swapped the whole lower - no change. I did blow thru the gas tube upon assembly and got what seemed to be expected flow. The tube seems free and straight, and when I removed the gas black to check alignment, the much larger hole in the gas block had left gas deposits around the barrel port that showed near-perfect placement. I have to ask this dumb question but did you swap it with a known working lower? Or did you swap parts between the two non working ar? If you swap known working lower and it still doesn't function we can say something is wrong with the upper. It def has to do with the gas key alignment or the front sight is loose and leaking gas. It could also be the barrel is loose in the reciever as well. Is the barrel nut torqued to spec? |
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Posted: 5/24/2015 11:36:23 PM EDT
[#20]
dalle0001
The end of the gas tube slides freely into the gas key (or visa-versa) - is that what you mean? It doesn't seem like a very tight fit though - how does it seal up? |
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Posted: 5/24/2015 11:40:01 PM EDT
[#21]
Quote HistoryQuoted:
I have to ask this dumb question but did you swap it with a known working lower? Or did you swap parts between the two non working ar? If you swap known working lower and it still doesn't function we can say something is wrong with the upper. It def has to do with the gas key alignment or the front sight is loose and leaking gas. It could also be the barrel is loose in the reciever as well. Is the barrel nut torqued to spec? Quote HistoryQuoted:
Quoted:
dalle0001 - The bolt carrier slide freely in the receiver, and the bolt seems to move with a resistance attributable to new gas rings. In any case, the BCG from the functioning unit did not help. As far as buffer, etc., I also swapped the whole lower - no change. I did blow thru the gas tube upon assembly and got what seemed to be expected flow. The tube seems free and straight, and when I removed the gas black to check alignment, the much larger hole in the gas block had left gas deposits around the barrel port that showed near-perfect placement. I have to ask this dumb question but did you swap it with a known working lower? Or did you swap parts between the two non working ar? If you swap known working lower and it still doesn't function we can say something is wrong with the upper. It def has to do with the gas key alignment or the front sight is loose and leaking gas. It could also be the barrel is loose in the reciever as well. Is the barrel nut torqued to spec? Swapped the entire lower (and BCG). Barrel is torqued to spec (almost 80 ft-lb before holes on the nut lined up). No front sight - free-float and scope. |
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Posted: 5/25/2015 12:10:08 AM EDT
[#22]
Quote HistoryQuoted:
ac130usnsr As I mentioned elsewhere, when I removed the gas block after several malfunctions, the "donut ring" mark around the barrel port showed near-perfect concentricity and plenty of extra room for misalignment. Still think that may be the problem? Alignment should be good then. Could be partially obstructed gas block or gas tube. Other possibility is gas tube is too loose in the gas block and more gas pressure is escaping around the end of the tube than through it. At this point, given everything you've explained, I would make sure your new bolt carrier groups work in your known working setup. Next, I would replace the gas blocks and gas tubes on the new builds. If that does not fix it, then I am at a loss as what you describe has to be caused be lack of enough gas pressure to fully cycle the BCG. Since this is happening on two identical builds that I can only assume were purchased at the same time and assembly errors have pretty much been ruled out, and the same failures happen when using a known good lower and BCG, then it has to be some sort of defect in the remaining parts of the gas system (gas block/gas tube). Best of luck. |
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Posted: 5/25/2015 12:36:48 AM EDT
[#23]
Quote HistoryQuoted:
Alignment should be good then. Could be partially obstructed gas block or gas tube. Other possibility is gas tube is too loose in the gas block and more gas pressure is escaping around the end of the tube than through it. At this point, given everything you've explained, I would make sure your new bolt carrier groups work in your known working setup. Next, I would replace the gas blocks and gas tubes on the new builds. If that does not fix it, then I am at a loss as what you describe has to be caused be lack of enough gas pressure to fully cycle the BCG. Since this is happening on two identical builds that I can only assume were purchased at the same time and assembly errors have pretty much been ruled out, and the same failures happen when using a known good lower and BCG, then it has to be some sort of defect in the remaining parts of the gas system (gas block/gas tube). Best of luck. Quote HistoryQuoted:
Quoted:
ac130usnsr As I mentioned elsewhere, when I removed the gas block after several malfunctions, the "donut ring" mark around the barrel port showed near-perfect concentricity and plenty of extra room for misalignment. Still think that may be the problem? Alignment should be good then. Could be partially obstructed gas block or gas tube. Other possibility is gas tube is too loose in the gas block and more gas pressure is escaping around the end of the tube than through it. At this point, given everything you've explained, I would make sure your new bolt carrier groups work in your known working setup. Next, I would replace the gas blocks and gas tubes on the new builds. If that does not fix it, then I am at a loss as what you describe has to be caused be lack of enough gas pressure to fully cycle the BCG. Since this is happening on two identical builds that I can only assume were purchased at the same time and assembly errors have pretty much been ruled out, and the same failures happen when using a known good lower and BCG, then it has to be some sort of defect in the remaining parts of the gas system (gas block/gas tube). Best of luck. I will try the new BCG in the working unit. If that works, I'll look into a new gas system. Maybe swap tube/block to good unit & see if problem follows it. Think anything could be wrong with (both) barrel's gas ports - burr obstructing inside or something? I'm grasping at straws at this point. Thanks for all your help, though. |
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Posted: 5/25/2015 1:02:17 AM EDT
[#24]
Quote HistoryQuoted:
I will try the new BCG in the working unit. If that works, I'll look into a new gas system. Maybe swap tube/block to good unit & see if problem follows it. Think anything could be wrong with (both) barrel's gas ports - burr obstructing inside or something? I'm grasping at straws at this point. Thanks for all your help, though. You can verify the gas ports on the new barrels by making sure you can see all the way through the gas port with no obstructions. Any burrs in the barrel should have been taken care of with the first round through the barrel, but you can verify by looking through the bore. Like I said before, since the new uppers paired with your good lower and good BCG exhibited the same problems, the problems have to be in the gas systems of the new uppers. |
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Posted: 5/25/2015 10:01:32 AM EDT
[#25]
Quote HistoryQuoted:
You can verify the gas ports on the new barrels by making sure you can see all the way through the gas port with no obstructions. Any burrs in the barrel should have been taken care of with the first round through the barrel, but you can verify by looking through the bore. Like I said before, since the new uppers paired with your good lower and good BCG exhibited the same problems, the problems have to be in the gas systems of the new uppers. Quote HistoryQuoted:
Quoted:
I will try the new BCG in the working unit. If that works, I'll look into a new gas system. Maybe swap tube/block to good unit & see if problem follows it. Think anything could be wrong with (both) barrel's gas ports - burr obstructing inside or something? I'm grasping at straws at this point. Thanks for all your help, though. You can verify the gas ports on the new barrels by making sure you can see all the way through the gas port with no obstructions. Any burrs in the barrel should have been taken care of with the first round through the barrel, but you can verify by looking through the bore. Like I said before, since the new uppers paired with your good lower and good BCG exhibited the same problems, the problems have to be in the gas systems of the new uppers. I think you may be on to something - I swapped the gas tube/block assemblies and noticed there seemed to signs of gas leakage between the new barrel and block - the working unit has zero signs of leakage. It almost looks like the barrel surface is not "round" around the port, but after I test fire hopefully I can tell if it is barrel shape, block shape or maybe both. I'll check my records and see where the gas block came from - I WAS pretty much going with lowest bidder on these builds (may be a lesson there!). |
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Posted: 5/25/2015 10:34:34 AM EDT
[#26]
Quote HistoryQuoted:
I think you may be on to something - I swapped the gas tube/block assemblies and noticed there seemed to signs of gas leakage between the new barrel and block - the working unit has zero signs of leakage. It almost looks like the barrel surface is not "round" around the port, but after I test fire hopefully I can tell if it is barrel shape, block shape or maybe both. I'll check my records and see where the gas block came from - I WAS pretty much going with lowest bidder on these builds (may be a lesson there!). I would say it is the gas block. Pretty hard for the barrel to be out of round since they are profiled by turning on a lathe, although, I guess the barrel journal could be out of spec (too small). I would really suspect the gas block is the culprit, especially if it was a cheap one. I'd recommend trying a Troy low profile if your barrels are dimpled for a set screw, otherwise I'd give an Vltor or Daniel Defense clamp on a try (the clamp ons are a little big on the bottom, check the inner diameter of your hand guard/rail to make sure it will fit). If you are using a railed gas block, I would recommend one of these. I've had good luck with them. |
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Posted: 5/25/2015 11:06:17 AM EDT
[#27]
OP, I'm just curious as to what buffer weights you are running on both the new builds and the working lower that you swapped out for testing purposes? You stated that these were mid-length uppers, so is it entirely possible that you may be running buffers that are too heavy and causing the short stroking? If you are running carbine buffers, and with all the information I have seen from the OP, I (like many others) believe this to be a gas issue. I would measure the roundness of the barrel at the gas block with a micrometer...then I'd shit-can the cheapo gas blocks and go from there. |
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Posted: 5/25/2015 11:39:26 AM EDT
[#28]
Yes, I was going to suggest you check the buffer and spring too. If the there is something binding in the receiver extension tube that would explain the symptoms too.
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Posted: 5/25/2015 12:25:24 PM EDT
[#29]
Quote HistoryQuoted:
OP, I'm just curious as to what buffer weights you are running on both the new builds and the working lower that you swapped out for testing purposes? You stated that these were mid-length uppers, so is it entirely possible that you may be running buffers that are too heavy and causing the short stroking? If you are running carbine buffers, and with all the information I have seen from the OP, I (like many others) believe this to be a gas issue. I would measure the roundness of the barrel at the gas block with a micrometer...then I'd shit-can the cheapo gas blocks and go from there. It sounds to me like a simple torquing issue where the gas block is coming loose. Probably not on tight enough or coming loose. Not sure what sort of low profile gas block he has but it sounds like the kind you screw in. If you can move the gas block with your hands, then it is not on tight enough. If I was the OP, I would get some loctite 246, and tighten down the screws. The loctite has a rating for up to 400 degrees and should be well enough for the gas block and to boost it is oil resistance. |
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Posted: 5/25/2015 12:35:34 PM EDT
[#30]
Quick update - fired 15 rds each (worky and no-worky), the problem did NOT follow the gas tube/block. The unit that worked before still works (although the ejection pattern seems different -more 2 oclock now than previous 4 oclock). The worst of the other two units now does at least eject most of the time, at about 4-5 oclock, but still won't chamber new round or lock bolt open on empty mag. The only things I haven't changed now are barrel and upper rec. (although not all at same time). Both of those have extended feed ramps that look to align fine. I will disassemble both units later today and check for signs of gas leaks to see if the new barrel may be causing it. Can't see how it could be the rec. fault, but now I'm into unlikely territory anyway.
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Posted: 5/25/2015 12:50:46 PM EDT
[#31]
With regard to buffers, all three are standard (carbine) m4 buffers and springs (adjustable stocks) no H on buffer face, look like 3 oz. The older working unit buffer spring IS shorter and maybe softer, but I just assumed that was because of more usage. In any case, that was actually my first thought so I swapped out the entire lowers - with no change. Block seems to fit snug, and was firmly held in place and loctited. I hope at this point it is lo-pro gas block/tube and not barrel, but the latest test does not seem to support that (see above). Jeeze!
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Posted: 5/25/2015 1:05:54 PM EDT
[#32]
I guess I could put everything back to original and swap barrels - that's about all I haven't tried. I'm going to have to make a testing muffler so I can check function at home - range trips to fire a few rounds are getting old.
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Posted: 5/25/2015 4:31:15 PM EDT
[#33]
Seems like you've tried everything, how about opening up your gas port a couple thousands?
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Posted: 5/25/2015 10:13:50 PM EDT
[#34]
Quote HistoryQuoted:
Seems like you've tried everything, how about opening up your gas port a couple thousands? If it turns out that it actually is the barrel, that is an option - but at .076", I thought it was about typical, which I am told is usually over-gassed. Maybe a chamber or bolt lug issue. Also, I read that it may help to polish the bore on new carriers. But I'll compare barrel port sizes and see if I might want to open it up. I guess I can always go to an adjustable block if it ends up over-gassed. I've got some more sleuthing to do. |
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Posted: 5/26/2015 2:41:33 PM EDT
[#35]
The problem is obviously with the gas system. Nothing else. Any possible lower or buffer/BCG alignment issue or gas key issue or any other grasp at straws has already been negated as a possible issue when the OP swapped known working good components from an old build to the new uppers and had the exact same issues.
OP, since your new gas block/gas tube combo moved to your old upper made it exhibit signs of slight over gassing (ejection change from 4-2 o'clock), they can likely be ruled out as the culprit for both an obstruction or gas leak. So, right now, by process of elimination, it's not the lowers, it's not the BCG or gas key, it's not the gas block and it's not the gas tube. Your new uppers are under gassed. Accurately measure the gas ports and make sure they measure the advertised 0.076". This should be the correct port size for 5.56 NATO ammo, however it may be under gassed for .223 Rem ammo. A gas port size of 0.078" seems to provide the best balance of not being over gassed for 5.56 ammo and reliably cycling most .223 ammo on a 16" mid length barrel. Make sure the gas port goes all the way through the barrel wall and into the bore with uniform diameter. If the gas port is not uniform or the advertised size then either contact the manufacturer or ream it out to spec, test again. If you are still short stroking, open it up a couple thousandths of an inch at a time then test. If none of this works, then I don't know what else it could be, as this will have addressed every possible issue. |
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Posted: 5/26/2015 3:03:36 PM EDT
[#36]
Quote HistoryQuoted:
The problem is obviously with the gas system. Nothing else. Any possible lower or buffer/BCG alignment issue or gas key issue or any other grasp at straws has already been negated as a possible issue when the OP swapped known working good components from an old build to the new uppers and had the exact same issues. OP, since your new gas block/gas tube combo moved to your old upper made it exhibit signs of slight over gassing (ejection change from 4-2 o'clock), they can likely be ruled out as the culprit for both an obstruction or gas leak. So, right now, by process of elimination, it's not the lowers, it's not the BCG or gas key, it's not the gas block and it's not the gas tube. Your new uppers are under gassed. Accurately measure the gas ports and make sure they measure the advertised 0.076". This should be the correct port size for 5.56 NATO ammo, however it may be under gassed for .223 Rem ammo. A gas port size of 0.078" seems to provide the best balance of not being over gassed for 5.56 ammo and reliably cycling most .223 ammo on a 16" mid length barrel. Make sure the gas port goes all the way through the barrel wall and into the bore with uniform diameter. If the gas port is not uniform or the advertised size then either contact the manufacturer or ream it out to spec, test again. If you are still short stroking, open it up a couple thousandths of an inch at a time then test. If none of this works, then I don't know what else it could be, as this will have addressed every possible issue. I totally agree. I was able to gage the new gas port - it is .076. The old (working) barrel is bigger - my .078" drill fits with room to spare. I am only shooting xm855 and xm 193, so I'm not sure why 076 isn't enough, but I went ahead and drilled out the new barrel port to .078" and will see how that works. |
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Posted: 5/26/2015 10:44:55 PM EDT
[#37]
Tried one round of xm193 - no eject. Hmmm...
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Posted: 5/26/2015 11:09:00 PM EDT
[#38]
Did it lock open?
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Posted: 5/26/2015 11:19:37 PM EDT
[#39]
How well does the bolt carrier move in the upper with the bolt removed? If it doesn't slide freely onto the gas tube and off again, that's a problem. Is the gas tube end damaged? The gas key?
I had a bolt carrier that had a little scuff on the gas key that did what you are describing. Sanded it smooth fixed it. I also had a bolt group that short stroked on mil ammo and i noticed the group didn't slide very well into the upper (new build), so i hand cycled the bolt group in the upper about 200 times with cutting oil and it smoothed up nice, no more short stroking, must of been a little tight on both tolerances. Just some thoughts. |
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Posted: 5/27/2015 1:30:26 AM EDT
[#40]
Quote HistoryQuoted:
Did it lock open? No, I had to manually eject the round. |
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Posted: 5/27/2015 1:44:42 AM EDT
[#41]
Quote HistoryQuoted:
How well does the bolt carrier move in the upper with the bolt removed? If it doesn't slide freely onto the gas tube and off again, that's a problem. Is the gas tube end damaged? The gas key? I had a bolt carrier that had a little scuff on the gas key that did what you are describing. Sanded it smooth fixed it. I also had a bolt group that short stroked on mil ammo and i noticed the group didn't slide very well into the upper (new build), so i hand cycled the bolt group in the upper about 200 times with cutting oil and it smoothed up nice, no more short stroking, must of been a little tight on both tolerances. Just some thoughts. BCG seems to cycle smooth by hand - with or without bolt. No visible damage to tube or key. Gas key actually seems a little loose (slides in very freely onto the tube) compared to the working unit (but swapping BCG did not help). I have hand cycled the BCG 50 to 100 times - the first few times did seem a little rough, but that has long since gone away. I'll try some more, though, that's easy enough. I think before I do any more drilling, I'll swap barrels to see if the issue follows the upper or the barrel. I'm an ex-mechanical engineer for Pete's sake, I'll get to the bottom of this if it's the last thing I do! |
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Posted: 5/27/2015 10:31:20 AM EDT
[#42]
You do have it properly lubed, right? I always run mine wet during break-in...
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Posted: 5/27/2015 1:04:31 PM EDT
[#43]
Quote HistoryQuoted:
You do have it properly lubed, right? I always run mine wet during break-in... Bolt to carrier to upper rec. all lubed up. |
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Posted: 5/27/2015 1:27:41 PM EDT
[#44]
Gas tube diameter undersized? That could create leakage at both ends...no?
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Posted: 5/27/2015 2:48:05 PM EDT
[#45]
Does the gas block have a set screw on the opposite side of the gas port? It sounds like the gas block isn't sealing against the barrel.
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Posted: 5/27/2015 4:17:55 PM EDT
[#46]
Quote HistoryQuoted:
Gas tube diameter undersized? That could create leakage at both ends...no? Yes, there were some signs of that - and when I swapped the tube/block to the working unit, it did seem the be somewhat less gassed - but it still worked fine. Comparing to the working unit, it seemed more that the gas key was over-sized rather than a small tube. Likely at least a part of the issue. |
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Posted: 5/27/2015 4:30:36 PM EDT
[#47]
Quote HistoryQuoted:
Does the gas block have a set screw on the opposite side of the gas port? It sounds like the gas block isn't sealing against the barrel. Yes to the screw (two-screw type). One of the two identical new units did show signs of gas leakage under the block, the other did not. Both tubes showed some leakage at each end. At one point I thought that was THE problem, but the short-stroking did not follow the tube/block assembly to the working unit in subsequent swaps. As I mentioned above, the only parts that haven't been swapped out are the barrel and upper receiver - logic says if I switch those one at a time, the problem should follow the culprit. Or, it's a combination of things, which may still continue to confound me. Or I'm an idiot and have done something bonehead you guys haven't discovered yet! The good thing is that now I can tear a gun apart and reassemble it behind my back 
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Posted: 5/27/2015 9:00:12 PM EDT
[#48]
I would go over the gas block with a light, and some twist drills to make sure that the holes are clean and bur free. The tapped hole under the gas hole, goes all the way into the gas tube hole. There could be a bur in there from machining.
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Posted: 5/27/2015 11:03:16 PM EDT
[#49]
Quote HistoryQuoted:
I would go over the gas block with a light, and some twist drills to make sure that the holes are clean and bur free. The tapped hole under the gas hole, goes all the way into the gas tube hole. There could be a bur in there from machining. I can see thru the block gas port into the tube port - they don't line up very well, but they are so much bigger than the barrel port I didn't think that would be a problem. However, in looking at the assembly from the working unit, it lines up perfectly. But putting the "perfect" block/tube onto the "bad" rifle did not make it cycle (although the "good" unit DID seem to cycle weaker with the "bad" block/tube). So let me think out loud: say that the bad block/tube diminishes pressure AND the smaller port on the barrel delivers less pressure AND the bigger bore gas key leaks some also - this might mean that good barrel can handle the two "leakers" and still cycle, but the bad barrel fails to cycle if EITHER of the two leaking parts is present - thus, swapping only one part at a time would always cause the bad barrel to fail. Am I making any sense? Now I find that I have tried so many combos with all three rifles that I'm not sure if I tried the re-drilled bad barrel with the proven carrier AND block/tube - I'm going to have to start keeping score  I was in the middle of swapping barrels/uppers, so I think I will go with:
Proven rifle with ONLY re-drilled new barrel (to evaluate the "bad" barrel) - if it works, start adding "new" parts to see if/when the problem returns. |
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Posted: 5/27/2015 11:43:19 PM EDT
[#50]
Is the gas block sitting to far back against the shoulder? Is the barrel designed to be used with a handguard cap? When you verified good gas block allignment how did you check?
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