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Posted: 3/29/2017 10:41:43 PM EDT
[#1]
Back to the range with a new gas tube--no more globs of carbon and grease all over the bolt after 20 rounds and....the gas key no longer strikes the tube.
Unfortunately, however, the single round lock-back test consistently failed with factory ammo and ejection was weak. Running a milspec carbine buffer tube and Aero spring/buffer. Tested a Sprinco orange and, well, it was worse. All signs point to under-gassing. Just to be sure, I removed the gas block (damned red loc-tite......and side pin....seemed like a good idea at the time!) and checked its alignment. Seemed dead on, but at least now I have double checked. I did confirm the Criterion gas port to be .096 exactly. Do these things require a break in? I've got maybe 80 rounds through it. Never needed this with any other rifle. If this does not work then the gas port may need enlarging. Never did this, but I'm sure people here have. Not something I want to do. Seems a last resort kind of thing. |
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Posted: 3/29/2017 10:55:36 PM EDT
[#2]
It was unfortunate, I was hoping you can solve your problem by replacing the gas tube and buffer. Did you try the Sprinco red spring? It may be easier just contact Criterion to open up the gas port. For a barrel >$300, they should take care of the customer.
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Posted: 3/29/2017 11:24:03 PM EDT
[#3]
Quote HistoryQuoted:
It was unfortunate, I was hoping you can solve your problem by replacing the gas tube and buffer. Did you try the Sprinco red spring? It may be easier just contact Criterion to open up the gas port. For a barrel >$300, they should take care of the customer. I've read some here say they enlarged the port to good effect with a simple hand drill and the right size bit. I suppose if all else fails...... I just looked up drill bit sizes: .096 is a #41. The next two larger are a #40 at .098 and 39 at .0995. Pretty sure I saw someone go even bigger. |
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Posted: 3/30/2017 8:54:25 AM EDT
[#4]
Quote HistoryQuoted:
Yes, thanks, I tried a red spring I brought. No appreciable difference. The new tube fit much better. No more contact with the BCG and normal carbon build up, so its a start. I have a call into Criterion. From what I've read the .096 port side may already be on the larger side. I'll see what they say before doing anything. I did double check my gas port when I got home. Seems fine to me. Centered and backed off the shoulder just the right amount. Verified the .096 myself. I've read some here say they enlarged the port to good effect with a simple hand drill and the right size bit. I suppose if all else fails...... I just looked up drill bit sizes: .096 is a #41. The next two larger are a #40 at .098 and 39 at .0995. Pretty sure I saw someone go even bigger. Go one bit at a time and then try the lock back test. Once it locks back then try shooting a full magazine. If you Google enough you will find there are plenty of reported gas ports larger than .096". In any event you can spend you life on here getting all kinds of opinions. You really have two choices: 1. - Keep trying different ammo until you find something that works. 2. - Drill the port one step at a time until you get your gun working on your ammo. There really is no rocket science here. You need more gas. More gas comes from a bigger hole, period. |
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Posted: 3/30/2017 9:10:51 AM EDT
[#5]
Quote HistoryQuoted:
Buy yourself the numbered drills #40, #39 and #38. Fractional bits are not good for this procedure. You can use a hand drill. The drill will follow the original hole just make sure you don't go too deep and hit the barrel opposite the hole. Put a peice of hose or wrap the bit with tape so you know when to stop. If using a drill press or a mill you can set a depth stop. Go one bit at a time and then try the lock back test. Once it locks back then try shooting a full magazine. If you Google enough you will find there are plenty of reported gas ports larger than .096". In any event you can spend you life on here getting all kinds of opinions. You really have two choices: 1. - Keep trying different ammo until you find something that works. 2. - Drill the port one step at a time until you get your gun working on your ammo. There really is no rocket science here. You need more gas. More gas comes from a bigger hole, period.  Attached File |
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Posted: 3/30/2017 9:41:53 AM EDT
[#6]
UPDATE:
I spoke to the VERY helpful "Mike" at Criterion and shared my pictures, experiences and attempts to date. His take: Its a timing issue, not necessarily a gas port issue. Enlarging the port is a way to brute force supply more gas, when was might be better are different buffers and springs. To that end we decided to try an AR10 style slightly longer buffer tube assembly, which allows one to use standard AR15 buffers. More customizable. Found some decent options on Palmetto State Armory. Just ordered it and will test upon arrival. |
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Posted: 3/30/2017 10:28:15 AM EDT
[#7]
Quote HistoryQuoted:
UPDATE: I spoke to the VERY helpful "Mike" at Criterion and shared my pictures, experiences and attempts to date. His take: Its a timing issue, not necessarily a gas port issue. Enlarging the port is a way to brute force supply more gas, when was might be better are different buffers and springs. To that end we decided to try an AR10 style slightly longer buffer tube assembly, which allows one to use standard AR15 buffers. More customizable. Found some decent options on Palmetto State Armory. Just ordered it and will test upon arrival. So you ordered just the tube (SKU: 506797) or the buffer assembly? From my reading, PSA's PA-10 set up is different than Armalite AR10 for the buffer system. The buffer tube is the same length which is the same as A5, but PA-10 spring is different than Armalite (1095). I cannot find exactly what spring PSA uses in their PA-10, but from the length and coils (11.25" and 27 coils), it is similar to DPMS 308 carbine spring. If you can get PA-10 buffer system to work with your gun, it may be due to the weaker spring (carbine spring will not get fully compressed in the tube, compared to Armalite 1095 spring). |
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Posted: 3/30/2017 10:40:11 AM EDT
[#8]
By the way, I have A5 tube with AR15 buffer and Armalite 1095 spring, I got short stroke (feeding and extracting fine, but bolt not lock back on empty magazine). I was suggested to try the DPMS carbine spring. DPMS rifle spring is too long. I have DMPS pattern rifle spring from Aero and tried it, the bolt face may be only 1/8" behind the bolt catch when spring is fully compressed. Unfortunate I do not have carbine spring, so will see your results first.
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Posted: 3/30/2017 10:52:54 AM EDT
[#9]
Quote HistoryQuoted:
Did he address the ding and scratch issue on the spent case? Is it possible there's burr in the chamber? I think it is less like the timing issue; they probably want you do more testing before they will take back the barrel. In this way it is all on your dime if you can get is resolved. So you ordered just the tube (SKU: 506797) or the buffer assembly? From my reading, PSA's PA-10 set up is different than Armalite AR10 for the buffer system. The buffer tube is the same length which is the same as A5, but PA-10 spring is different than Armalite (1095). I cannot find exactly what spring PSA uses in their PA-10, but from the length and coils (11.25" and 27 coils), it is similar to DPMS 308 carbine spring. If you can get PA-10 buffer system to work with your gun, it may be due to the weaker spring (carbine spring will not get fully compressed in the tube, compared to Armalite 1095 spring). The AR10 tube, which is about 5/8 or so longer, allows standard AR buffers: H, H2 and H3, etc and AR springs. I will re-test with the new buffer tube and an assortment of buffers and springs. I ordered the 506798 assembly consisting of tube, buffer and spring, etc. http://palmettostatearmory.com/psa-pa10-buffer-tube-assembly.html |
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Posted: 3/30/2017 11:19:21 AM EDT
[#10]
Quote HistoryQuoted:
He did specifically address it and thinks its a lock time issue, i.e. bolt coming back before pressure is down. His explanation made sense. Said he is doing the AR10 work and spends much of his day addressing these issues. Got the impression f an enthusiast really trying to help. I in no way think he is delaying. Just the opposite. Their port size is a bit bigger on average. His think people enlarge too quickly when there are other, less permanent and more effective solutions. The AR10 tube, which is about 5/8 or so longer, allows standard AR buffers: H, H2 and H3, etc and AR springs. I will re-test with the new buffer tube and an assortment of buffers and springs. I ordered the 506798 assembly consisting of tube, buffer and spring, etc. http://palmettostatearmory.com/psa-pa10-buffer-tube-assembly.html But I am not convinced that it's lock time issue, or because of this causing the dent. If bolt coming back too early before pressure is down, a stronger spring should be used so it can hold the bolt close a little bit longer. But your experiment with Orange spring proved that stronger spring make the thing worse. Your barrel is a little bit unusual for a 16" with rifle length gas, it is more sensitive to other factors due to very short dwell time. 0.096" may be fine for 18" or 20", but may be small for 16". |
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Posted: 3/30/2017 11:28:34 AM EDT
[#11]
Quote HistoryQuoted:
Then you have more springs and buffers to test out. Please do update with the results. I am also curious to see the comparison of PA-10 spring with Aero DMPS pattern carbine spring. But I am not convinced that it's lock time issue, or because of this causing the dent. If bolt coming back too early before pressure is down, a stronger spring should be used so it can hold the bolt close a little bit longer. But your experiment with Orange spring proved that stronger spring make the thing worse. Your barrel is a little bit unusual for a 16" with rifle length gas, it is more sensitive to other factors due to very short dwell time. I figure I'll try the simpler fixes, and like the idea of using standard AR buffers anyway, which allows for more flexibility. |
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Posted: 3/30/2017 2:22:33 PM EDT
[#12]
I went to the range today during lunch break to test out, and wanted to report back. I got the 308 to run with no issue, and bolt can lock back on empty magazine. I used the same 147gr ammo, same magazine and spring. I did two things after last test: 1) clean the chamber one more time with copper brush; 2) lubricate more the BCG, and use white lithium grease on the outside rails on BCG. I did hand cycle the BCG maybe 20-30 times.
I started with carbine buffer with one rd in the magazine and it locked back fine, then one step a time from H1 to H3 buffer without issue. I today actually brought DPMS 308 rifle spring and pliers with me and ready to cut the coils if it still did not work. Seemed like the gun is ok for the moment. Above may be helpful to your case, and very interested to see your final findings and solution. |
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Posted: 3/30/2017 6:59:53 PM EDT
[#13]
Quote HistoryQuoted:
I went to the range today during lunch break to test out, and wanted to report back. I got the 308 to run with no issue, and bolt can lock back on empty magazine. I used the same 147gr ammo, same magazine and spring. I did two things after last test: 1) clean the chamber one more time with copper brush; 2) lubricate more the BCG, and use white lithium grease on the outside rails on BCG. I did hand cycle the BCG maybe 20-30 times. I started with carbine buffer with one rd in the magazine and it locked back fine, then one step a time from H1 to H3 buffer without issue. I today actually brought DPMS 308 rifle spring and pliers with me and ready to cut the coils if it still did not work. Seemed like the gun is ok for the moment. Above may be helpful to your case, and very interested to see your final findings and solution. Thank you for this picture. You really can make some good observations when reading a piece of brass. What I see from the picture is some minor marring on the rim of the brass caused by the extractor as it pulls the brass out of the chamber (though the picture didn’t come through in high resolution). I do believe that you are having some issues with lock time (spring and buffer weight) as there is minor scuffing about 2/3 up the body of the brass where the shoulder and neck area of the brass had expanded and was then pulled out of the chamber before it had a chance to shrink back down. I also see the scratches you were referring to on the neck of the brass, this is common in gas guns because of the method of feeding, though it is also a common issue when the bolt carrier is moving back more slowly than what would be ideal and the brass is dragged out of the chamber and directed into the feed ramps/barrel extension which can cause marring. Overall, I think that any lock time issues appear to be fairly minor and that slight tweaking will get your rifle running smoothly. I look forward to hearing about your results. We will be in touch. |
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Posted: 3/30/2017 7:07:24 PM EDT
[#14]
Interesting usage of the "lock time" terminology.
That's generally limited to mean the time between the release of the hammer and the ignition of the primer. 
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Posted: 3/30/2017 7:32:55 PM EDT
[#15]
Quote HistoryQuoted:
Interesting usage of the "lock time" terminology. That's generally limited to mean the time between the release of the hammer and the ignition of the primer. Gun Digest: https://books.google.com/books?id=MQw5AwAAQBAJ&pg=PA98&lpg=PA98&dq=ar15+lock+time+definition&source=bl&ots=dpiW52cdBd&sig=lk-MIGuGQFfGn53Efp6CMklRr2c&hl=en&sa=X&ved=0ahUKEwi-3vrUsP_SAhXm3YMKHcS3DNYQ6AEINDAE#v=onepage&q=ar15%20lock%20time%20definition&f=false |
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Posted: 3/30/2017 8:45:01 PM EDT
[#16]
I had a similar problem with my LR308 build. Except it would not load 2nd round nor lock back on the last round.
I have an adjustable gas block, I opened it all the way with same result. Check gas port alignment over and over again that was not problem My barrel is Rainier Arm Ultra Match 20 inch. At the end, what fixed the problem was gas port on the barrel was undersized. I believed I open up to 0.100" (I could be wrong, this was 3-4 years ago). If you can lock the bolt back by hand it is not bottom out on the buffer tube. It could be your rifle is slightly under-gassed. PS. I also found the POF roller cam pin smooth out bolt carrier movement, it was very tight and rough on the regular one, not that you must have it. |
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Posted: 3/30/2017 8:53:03 PM EDT
[#17]
Quote HistoryQuoted:
I had a similar problem with my LR308 build. Except it would not load 2nd round nor lock back on the last round. I have an adjustable gas block, I opened it all the way with same result. Check gas port alignment over and over again that was not problem My barrel is Rainier Arm Ultra Match 20 inch. At the end, what fixed the problem was gas port on the barrel was undersized. I believed I open up to 0.100" (I could be wrong, this was 3-4 years ago). If you can lock the bolt back by hand it is not bottom out on the buffer tube. It could be your rifle is slightly under-gassed. PS. I also found the POF roller cam pin smooth out bolt carrier movement, it was very tight and rough on the regular one, not that you must have it. Figure I'll try the longer AR10 buffer tube & standard H, H2 &H3 buffers before drilling, which I cannot undo. If such does not work, then I will likely join you in incrementally opening up the port. If so, I'll install a JP adjustable gas block. Curious- what was your barrel at when you started? Criterion, who I am getting to like quite a bit for their service, starts at .096. Did you work up to 0.100 and test or just start there? |
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Posted: 4/4/2017 5:31:02 PM EDT
[#18]
Well, it was a few years back, so I don't remember the original port size. I believe it was around .094-.096.
You definitely would not want to go too big. As I remember my gas block mating port was much bigger. If you go a bit too large, you could get a adjustable gas block, so you are wasting a good barrel. Just be very careful not to hit the inside of the barrel when you drill. |
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Posted: 4/5/2017 12:00:41 AM EDT
[#19]
Quote HistoryQuoted:
Well, it was a few years back, so I don't remember the original port size. I believe it was around .094-.096. You definitely would not want to go too big. As I remember my gas block mating port was much bigger. If you go a bit too large, you could get a adjustable gas block, so you are wasting a good barrel. Just be very careful not to hit the inside of the barrel when you drill. Going to try the buffer/spring mods first at the suggestion of Criterion and Lantec. If this does not work....well, maybe its time to get out the drill. Go from 0.096 up one size. From what I read, 0.096 is a #40. The next up is a #41 at 0.098. After that we have #39 at 0.0995 and so on. |
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Posted: 4/5/2017 3:10:55 AM EDT
[#20]
Quote HistoryQuoted:
Sound advice!! Put a dowel or something in the barrel. Make for an interesting accuracy goal, however. Going to try the buffer/spring mods first at the suggestion of Criterion and Lantec. If this does not work....well, maybe its time to get out the drill. Go from 0.096 up one size. From what I read, 0.096 is a #40. The next up is a #41 at 0.098 which also happens to be 17/64". After that we have #39 at 0.0995 and so on. 7/64" isn't the same as a #41. This should help. #41 - 0.0960" #40 - 0.0980" #39 - 0.0995" #38 - 0.1015" #37 - 0.1040" #36 - 0.1065" 7/64" - 0.1094" |
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Posted: 4/5/2017 9:49:39 AM EDT
[#21]
Quote HistoryQuoted:
I hope you meant 7/64" instead of 17/64". That would be one gigantic gas port. Lol. 7/64" isn't the same as a #41. This should help. #41 - 0.0960" #40 - 0.0980" #39 - 0.0995" #38 - 0.1015" #37 - 0.1040" #36 - 0.1065" 7/64" - 0.1094" Site used: http://www.engineersedge.com/drill_sizes.htm |
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Posted: 4/5/2017 2:21:15 PM EDT
[#22]
Once you get ready to drill make sure to not hit the barrel opposite the port. Clean the barrel and then go test. Go one drill size at a time until you get it functioning.
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Posted: 4/5/2017 2:24:55 PM EDT
[#23]
REVISED TESTING RESULTS:
Had a modest range session today to experiment with different springs and buffer, etc. after swapping the buffer tube for the 3/4" longer AR10 tube. Used a variety of ammo (Federal 150g, Prvi 147g and old Federal Gold 168g) Best success with mostly 4 o'clock ejection and multiple 1 round lock open tests was this: Red "Sprinco" brand spring and standard H2 buffer. Orange spring failed to lock back regularly. Approximately 40 rounds- No failures, lock back every time and successfully chambering new rounds. Fingers crossed. Next tests will be for repeatable accuracy. |
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Posted: 4/5/2017 3:19:07 PM EDT
[#24]
Quote HistoryQuoted:
REVISED TESTING RESULTS: Had a modest range session today to experiment with different springs and buffer, etc. after swapping the buffer tube for the 3/4" longer AR10 tube. Used a variety of ammo (Federal 150g, Prvi 147g and old Federal Gold 168g) Best success with mostly 4 o'clock ejection and multiple 1 round lock open tests was this: Red "Sprinco" brand spring and standard H2 buffer. Orange spring failed to lock back regularly. Approximately 40 rounds- No failures, lock back every time and successfully chambering new rounds. Fingers crossed. Next tests will be for repeatable accuracy. All the other springs are not able to reliably lock open the bolt, including the short Aero 308 carbine spring? |
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Posted: 4/5/2017 5:27:06 PM EDT
[#25]
Quote HistoryQuoted:
Congratulations! Ar least your can leave drilling the gas port out for the moment, and enjoy your rifle. All the other springs are not able to reliably lock open the bolt, including the short Aero 308 carbine spring? |
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