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Posted: 7/21/2024 7:52:13 PM EST
[#1]
Is the gas port drilled?
Is the gas block over the port? Is the gas key loose? |
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Posted: 7/21/2024 8:08:49 PM EST
[#2]
Quote HistoryQuoted: Is the gas port drilled? Is the gas block over the port? Is the gas key loose? Everything is good with the GB aside from verifying it came loose as I have not checked that yet. |
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Posted: 7/21/2024 9:46:03 PM EST
[#3]
Quote HistoryQuoted: Everything is good with the GB aside from verifying it came loose as I have not checked that yet. Check to make sure you have the right length gas tube and that it has the proper bell flare on the end. Check the gas key to ensure it is tight, not leaking and has the proper internal thickness so it doesn't leak too much gas outside the gas tube. Check for gas rings on the bolt to make sure they're in place. Can you post pics of your rifle, upper, bolt carrier group, bolt and looking inside of your upper with the bolt removed (from the bottom)? |
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Posted: 7/21/2024 9:47:46 PM EST
[#4]
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Posted: 7/21/2024 11:54:08 PM EST
[#5]
Start at square one. Put your standard BCG in it. See if that works. Even if it doesn't, I'd leave it there while you troubleshoot. You can worry about fancy shit later.
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Posted: 7/22/2024 1:26:09 AM EST
[#6]
From you description sounds like your carrier isn't moving at all is that correct?
Put a standard gas tube on it. How did you select the BRT gas tube port size? Honestly this is the kind of stuff that happens when you start messing with a perfectly fine system. |
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Posted: 7/22/2024 4:57:58 AM EST
[#7]
Load one round and see if the BCG lock back.
Of OP list I’d replace the BCG, gas tube and recoil spring with standard components and see if it runs… then put back the custom parts one at the time, test fire and find the culprit. |
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Posted: 7/22/2024 6:22:32 AM EST
[#8]
If the gas block is installed correctly it can only be two things 99% of the time.
If the carrier does not move AT ALL... gas tube installed upside down. If it only moves a little. Gas port size of tube is wrong on your BRT gas tube. |
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Posted: 7/22/2024 6:43:11 AM EST
[#9]
You might want to video capture the port to see if the bolt is moving back and how much, it might just be short stroking (not even far enough to eject and closing) due to some loss of gas - and the fix is as the other suggestions. Gas block alignment, tightness, port size, rings in BCG
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Posted: 7/22/2024 7:33:24 AM EST
[#10]
All good advice, also make sure the roll pin for the gas tube is present and gas tube wont move at all. I've seen single shot issues when the roll pin is missing.
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Posted: 7/22/2024 10:40:48 AM EST
[#11]
12.5"
+ Mid-length gas + Restrictive gas tube + G42 spring + .223 ammo Seems like a recipe for unreliability. |
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Posted: 7/22/2024 11:55:42 AM EST
[#12]
Did some napkin math, using a variety of commonly used ammunition. A 12.5”-14.5” carbine gassed gun, 16” middy, or 20” rifle are all in somewhat similar neighborhoods when it comes to how long the gas port is pressurized, just considering the time from the bullet passing the port to exiting the muzzle. Around 0.2ms on average. Even if I manipulate ammo choice to attempt to make the situation less unfavorable to a 12.5” middy, the time the gas port is pressurized is less than half that common in more conventional systems; around 0.1ms. This is all simplified and rounded for clarity’s sake.
Of course, this does nothing to solve the OP’s problem, but illustrates why no one should be surprised if extreme port location to barrel length ratios (12.5” mid) are finicky or unforgiving, in comparison to conventional setups. A 12.5” carbine gas is slightly more forgiving than 14.5” mid in this math, so not a tough nut to crack at all. It’s between a 14.5” carbine and 14.5” mid in how long the gas port is pressurized. A 12.5” mid is less forgiving than a 10.3” carbine by these metrics, so not a particularly great idea. |
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Posted: 7/22/2024 12:02:01 PM EST
[#13]
12.5 mid is fine if the gas port is sized correctly.
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Posted: 7/22/2024 12:10:45 PM EST
[#14]
Quote HistoryQuoted: 12.5 mid is fine if the gas port is sized correctly. OP, I think you’ve already gotten good advice on inspecting the gas system for major leaks. I’ll add that swapping in the BCG from your other rifle, or a regular middy gas tube might help your troubleshooting. And a regular, plain-Jane action spring. |
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Posted: 7/22/2024 4:50:32 PM EST
[#15]
Quote HistoryQuoted: Did some napkin math, using a variety of commonly used ammunition. A 12.5”-14.5” carbine gassed gun, 16” middy, or 20” rifle are all in somewhat similar neighborhoods when it comes to how long the gas port is pressurized, just considering the time from the bullet passing the port to exiting the muzzle. Around 0.2ms on average. Even if I manipulate ammo choice to attempt to make the situation less unfavorable to a 12.5” middy, the time the gas port is pressurized is less than half that common in more conventional systems; around 0.1ms. This is all simplified and rounded for clarity’s sake. Of course, this does nothing to solve the OP’s problem, but illustrates why no one should be surprised if extreme port location to barrel length ratios (12.5” mid) are finicky or unforgiving, in comparison to conventional setups. A 12.5” carbine gas is slightly more forgiving than 14.5” mid in this math, so not a tough nut to crack at all. It’s between a 14.5” carbine and 14.5” mid in how long the gas port is pressurized. A 12.5” mid is less forgiving than a 10.3” carbine by these metrics, so not a particularly great idea. OP this is good info ^ I think some 12.5 mid barrels can be good to go; I would trust an LMT or Sionics, but would stray away from questionable brands. I'd also add that apart from the 12.5 middy (which can be closer to the edge of reliability vs a carbine gas 12.5) your low mass BCG probably isn't helping. Is there a reason you're using a low mass BCG for this SBR? If this is really a HD rifle, I would stick to a more conventional/boring setup. |
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Posted: 7/22/2024 4:52:41 PM EST
[#16]
Quote HistoryQuoted: OP this is good info ^ I think some 12.5 mid barrels can be good to go; I would trust an LMT or Sionics, but would stray away from questionable brands. I'd also add that apart from the 12.5 middy (which can be closer to the edge of reliability vs a carbine gas 12.5) your low mass BCG probably isn't helping. Is there a reason you're using a low mass BCG for this SBR? If this is really a HD rifle, I would stick to a more conventional/boring setup. ETA: I know your original post said "without ditching the low mass BCG...". I think the advice you got so far is good. I am genuinely curious in your reasoning for the low mass BCG for this role though. |
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Posted: 7/22/2024 5:01:19 PM EST
[#17]
Quote HistoryQuoted: From you description sounds like your carrier isn't moving at all is that correct? Put a standard gas tube on it. How did you select the BRT gas tube port size? Honestly this is the kind of stuff that happens when you start messing with a perfectly fine system. Kind of my thoughts... In years of doing classes, by far the most problems I see are from rifles with non-standard parts. |
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Posted: 7/22/2024 7:23:19 PM EST
[#18]
In a silly question but did you make sure the adjustable gas block is in the open position?
I would first mess with the gas block and tube. Also is there carbon in the bolt and carrier? If not, it would mean no gas is going back there at all. You can usually tell if at least gas is flowing back there because of the build up. Sometimes you can tell if something is off with the carrier depending on how much carbon is built up. |
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Posted: 7/22/2024 8:43:31 PM EST
[#19]
Quote HistoryQuoted: In a silly question but did you make sure the adjustable gas block is in the open position? . 2 seperate coworkers have brought ARs to me to diagnose because the carrier would barely open. Saw that they were adjustable gas blocks. Both were set to the closed position. I opened them to full open and handed them back and told them to try them. The week after each had brought me their rifles, both said they worked great. Imagine that. My personal opinion about adjustable gas blocks is that if you don't plan on using a suppressor, an adjustable block is a waste of money. 2 of my rifles have cans. Both have adjustable blocks. The other 5 or 6 ARs have plain Jane low profile blocks or front sight post gas blocks. |
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Posted: 7/22/2024 9:15:40 PM EST
[#20]
OP doesn’t have an adjustable gas block…
OP, what size gas tube did BRT set you up with? I have an 11.5” mid, (Noveske) dedicated suppressor set up (YHM K2), they sent me an 0.067 gas tube and it works perfectly. Just curious what size they sent you. |
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Posted: 7/22/2024 9:37:04 PM EST
[#21]
You have too much going on with aftermarket parts to nail it down. Any or all could be the problem. Easiest first step is to put a std BCG and spring in it. See what happens. If that doesn't do it, swap in a std tube. (Fyi) If you want to run a light weight carrier, a stiff spring is going the wrong direction. You want a lighter spring.
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Posted: 7/23/2024 12:22:05 AM EST
[#22]
Quote HistoryQuoted: OP doesn’t have an adjustable gas block… OP, what size gas tube did BRT set you up with? I have an 11.5” mid, (Noveske) dedicated suppressor set up (YHM K2), they sent me an 0.067 gas tube and it works perfectly. Just curious what size they sent you. Oops. Thought there was an adjustable gas block listed. Never mind. |
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Posted: 7/23/2024 8:05:58 AM EST
[#23]
Quote HistoryQuoted: You have too much going on with aftermarket parts to nail it down. Any or all could be the problem. Easiest first step is to put a std BCG and spring in it. See what happens. If that doesn't do it, swap in a std tube. (Fyi) If you want to run a light weight carrier, a stiff spring is going the wrong direction. You want a lighter spring. I run Super 42 in everything. I have a Strike flatwire spring I can try. |
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Posted: 7/23/2024 8:07:42 AM EST
[#24]
I checked the GB and while it didn't move and wouldn't mive by hand, it mived by tapping it with a mallet. I reinstalled the set screws with new vibratite.
Maybe that was it. |
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Posted: 7/23/2024 8:12:45 AM EST
[#25]
Quote HistoryQuoted: I checked the GB and while it didn't move and wouldn't mive by hand, it mived by tapping it with a mallet. I reinstalled the set screws with new vibratite. Maybe that was it. Was there a carbon ring around the port? As in properly aligned? If the carrier moves freely when you pull the charging handle but does not move at all when firing then it isn't getting any gas. |
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Posted: 7/23/2024 8:26:50 AM EST
[#26]
Quote HistoryQuoted: OP doesn’t have an adjustable gas block… OP, what size gas tube did BRT set you up with? I have an 11.5” mid, (Noveske) dedicated suppressor set up (YHM K2), they sent me an 0.067 gas tube and it works perfectly. Just curious what size they sent you. They sent me .067 as well |
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Posted: 7/23/2024 8:27:18 AM EST
[#27]
Quote HistoryQuoted: Was there a carbon ring around the port? As in properly aligned? If the carrier moves freely when you pull the charging handle but does not move at all when firing then it isn't getting any gas. |
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Posted: 7/23/2024 8:27:33 AM EST
[#28]
Quote HistoryQuoted: Was there a carbon ring around the port? As in properly aligned? If the carrier moves freely when you pull the charging handle but does not move at all when firing then it isn't getting any gas. GB is properly aligned and tube is properly installed. I didn't see any carbon, but I only fired 3 or 4 rounds |
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Posted: 7/23/2024 8:57:18 AM EST
[#29]
Quote HistoryQuoted: From you description sounds like your carrier isn't moving at all is that correct? Put a standard gas tube on it. How did you select the BRT gas tube port size? Honestly this is the kind of stuff that happens when you start messing with a perfectly fine system. This. 12.5" mid-length is going to be short on gas already. The fancy gas tube is the likely culprit. Put in a standard gas tube, a standard spring and a standard carrier and it should run. After that, if you want to tune it down and run the light carrier, get one of the many good adjustable gas block options. |
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Posted: 7/23/2024 8:59:38 AM EST
[#30]
Quote HistoryQuoted: GB is properly aligned and tube is properly installed. I didn't see any carbon, but I only fired 3 or 4 rounds I'm assuming you're basing that off the dimples. I prefer to go off carbon because while rare it is possible the dimples are drilled off center. Again if you can hand cycle the carrier freely with the charging handle and gun assembled, but the carrier doesn't move AT ALL when firing, then the issue is in the gas system. Gas port. Gas block. Gas tube. Gas key. Though I find it very unlikely it's the key with no movement at all. |
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Posted: 7/23/2024 9:03:01 AM EST
[#31]
Clearly a gas issue if the carrier isn't moving. Start with the port/gas block/ gas tube. It's got to be one of those, or a combination.
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Posted: 7/23/2024 9:07:37 AM EST
[#32]
FYI, when John Thomas cuts SOCOM barrels down to 12.5 for me I ask him for a .066 port. They run flawlessly, albeit with a carbine gas system. Hope this helps.
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Posted: 7/23/2024 9:08:31 AM EST
[#33]
Quote HistoryQuoted: Clearly a gas issue if the carrier isn't moving. Start with the port/gas block/ gas tube. It's got to be one of those, or a combination. And what exactly am I supposed to do? Everything is installed properly. This isn't my first time building a rifle. Maybe the tube itself is the problem |
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Posted: 7/23/2024 9:11:22 AM EST
[#34]
Quote HistoryQuoted: And what exactly am I supposed to do? Everything is installed properly. This isn't my first time building a rifle. Maybe the tube itself is the problem Pull the non-standard parts and put them in a box in the closet. You're undergassed for one reason or another. What do you think might cause that?..... 12.5 mid-length should have a ~0.084-0.086" gas port. With a 0.067" orifice insert you're cutting the gas port area by ~60% |
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Posted: 7/23/2024 9:11:34 AM EST
[#35]
Quote HistoryQuoted: And what exactly am I supposed to do? Everything is installed properly. This isn't my first time building a rifle. Maybe the tube itself is the problem Use the process of elimination. Start by measuring the port size, block alignment, replacing the tube, then the block--keeping all other variables constant--until you get it running. |
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Posted: 7/23/2024 9:13:21 AM EST
[#36]
I've never bought a Faxon barrel, I'd want to confirm that port size to begin with. Pin gauges or a drill bit can give you an idea.
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Posted: 7/23/2024 9:30:21 AM EST
[#37]
Quote HistoryQuoted: I've never bought a Faxon barrel, I'd want to confirm that port size to begin with. Pin gauges or a drill bit can give you an idea. Port diameter in the BRT tube trumps the barrel GP diameter. OP, swap the gas tube. 10 minutes time could save you much headache. |
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Posted: 7/23/2024 9:42:01 AM EST
[#38]
Quote HistoryQuoted: Pull the non-standard parts and put them in a box in the closet. You're undergassed for one reason or another. What do you think might cause that?..... 12.5 mid-length should have a ~0.084-0.086" gas port. With a 0.067" orifice insert you're cutting the gas port area by ~60% |
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Posted: 7/23/2024 11:24:27 AM EST
[#39]
Quote HistoryQuoted: 12.5 mid-length should have a ~0.084-0.086" gas port. To run lightly loaded ammo unsuppressed, perhaps. |
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Posted: 7/23/2024 11:34:36 AM EST
[#40]
I'll start with swapping to a standard gas tube and see what happens
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Posted: 7/23/2024 12:03:39 PM EST
[#41]
Gas block hole is misaligned with gas port. I will put money on it. Even an extremely reduced gas port size through a BRT gas tube will still cycle a suppressed SBR.
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Posted: 7/23/2024 1:11:35 PM EST
[#42]
Quote HistoryQuoted: Gas block hole is misaligned with gas port. I will put money on it. Even an extremely reduced gas port size through a BRT gas block will still cycle a suppressed SBR. I agree with this, something isn't right. I also agree with returning everything to standard parts and changing one thing at a time to figure it out. Not dogging OP’s build skills just attempting to help diagnose this. The G 42 spring needs to go, the last thing you want in a setup of this kind is an extra power spring or heavy buffer as it defeats the purpose. I would ditch the spring, use a standard spring, carbine buffer and really take a look at that gas block. Once you feel like it is good to go, I would put an earplug in the chamber and run air through the muzzle to test the alignment and make sure the system works as in air is coming out of the gas tube. The BRT gas tube should be gtg especially suppressed. The fact that it doesn’t even cycle lends its self to something being wrong or out of spec. The BRT tube at .067 is a 40% reduction in gas flow from a .086 gas port. |
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Posted: 7/23/2024 2:07:21 PM EST
[#43]
Quote HistoryQuoted: I agree with this, something isn't right. I also agree with returning everything to standard parts and changing one thing at a time to figure it out. Not dogging OP’s build skills just attempting to help diagnose this. The G 42 spring needs to go, the last thing you want in a setup of this kind is an extra power spring or heavy buffer as it defeats the purpose. I would ditch the spring, use a standard spring, carbine buffer and really take a look at that gas block. Once you feel like it is good to go, I would put an earplug in the chamber and run air through the muzzle to test the alignment and make sure the system works as in air is coming out of the gas tube. The BRT gas tube should be gtg especially suppressed. The fact that it doesn’t even cycle lends its self to something being wrong or out of spec. The BRT tube at .067 is a 40% reduction in gas flow from a .086 gas port. From what he explained, the BCG isn’t moving at all. That is gas issue. Gas block not aligned, gas block walked loose, gas tube installed wrong (not sure how), blockage in the gas tube. It has to be one of those things. No gas is getting to the gas key on BCG to cycle. |
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Posted: 7/23/2024 2:12:27 PM EST
[#44]
Quote HistoryQuoted: I checked the GB and while it didn't move and wouldn't mive by hand, it mived by tapping it with a mallet. I reinstalled the set screws with new vibratite. Maybe that was it. It shouldn’t move with a mallet or a ball peen hammer. There is your problem. How are you verifying the gas block is aligned to TDC? If you used any kind of thread locker just assuming your gas block is TDC, you might have added some extra work. |
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Posted: 7/23/2024 3:45:44 PM EST
[#45]
I swapped the BRT tube for an off the shelf mid-length tube. I'll also swap the 42 spring with a flatwire I have collecting dust.
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Posted: 7/23/2024 4:09:27 PM EST
[#46]
Agree that if the carrier is not moving at all, it isn't a question of tuning port sizes or springs or whatnot... I would say you have a total blockage. Either something is completely misaligned, or one of the gas system parts has a manufacturing defect/isn't ported all the way through.
You could replace one part at at time, and/or try the string trimmer line through the gas block, tube, carrier key, etc. |
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Posted: 7/25/2024 10:23:42 AM EST
[#47]
If you specified that you are running suppressed and unsuppressed with a 12.5" barrel, and they sent you a .067, you're likely undergassed in the first place. That size is appropriate of a carbine length gas system.
Vibratite is not an appropriate thread locker for your purpose. If you are using screws that are black, red loctite would be more appropriate. If using stainless set screws, you might consider rocksett. Red loctite could work, but it doesn't hold on to stainless very well. I really don't know what all the rage is with the BRT gas tube's. You would have spent less money in the long run just getting a quality adjustable gas block. I'd properly affix the gas block and replace the gas tube with a milspec tube. Get rid of that lightweight carrier. It's counterproductive when running a suppressed rifle. You want weight and spring tension to insure proper cycling of a dirty rifle. With a quality barrel and anything even close to a properly sized gas port, the most you should need to modify is going with an H3 or A5H4 buffer to get proper operation. |
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Posted: 7/25/2024 11:06:33 AM EST
[#48]
Quote HistoryQuoted: I really don't know what all the rage is with the BRT gas tube's. You would have spent less money in the long run just getting a quality adjustable gas block. Link to a quality adjustable GB that rings in at ~$50? |
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Posted: 7/25/2024 11:20:14 AM EST
[#49]
Quote HistoryQuoted: Link to a quality adjustable GB that rings in at ~$50? If you don't need levers and knobs, just set and forget, there are plenty of options... Several options here |
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Posted: 7/25/2024 11:54:00 AM EST
[#50]
Quote HistoryQuoted: If you don't need levers and knobs, just set and forget, there are plenty of options... Several options here Quote HistoryQuoted: Quoted: Link to a quality adjustable GB that rings in at ~$50? If you don't need levers and knobs, just set and forget, there are plenty of options... Several options here Thanks. I have an Aero that I'm trying out but no significant round count on it yet. BRT tubes on other guns. Adjustable blocks and "set it and forget it" mentality vs preset gas tubes is a strange theory in my mind, especially when the majority of adjustable blocks run near twice the cost of a tube. To each their own though. Good to have options. |
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