View Full Version : SME Help needed; Gas Port Size
Sparky5019
10-14-23, 14:06
Situation:
I built a customer a perfect 10.3” Geissele upper group that was perfect (parts listed below).
Geissele upper
Geissele 10.3 barrel (0.069” port)
SLR sentry 7 AGB taper pinned
Geissele BCG w/ JP gas ring
Geissele MK8 handguard
Geissele ABCH
Surefire SOCOM Closed tine MD
Surefire SOCOM556-RC2
He does use a JP SCS in the lower. More on that later.
Upper runs flawlessly suppressed/unsupressed with any ammo (pending slight adjustment to the AGB). It runs flawlessly for 1000s of rounds. He wants the shoulder on the barrel set back to move the can closer to the rail and make the gun slightly more compact. He takes the gun to a LGS hack (without calling me to ask an opinion or to help him), and the guy proceeds to f*ck up not just my work but make the upper not lock back with any ammo under any conditions. This guy even punched my taper pin all the way through from the WRONG side (put in just like FSB pins). Can ya tell I’m a little pissed? lol It’s a damn miracle the new shoulder was in the right place and actually straight but somehow it was. The muzzle crown and threads were jacked up and I had ADCO fix that (since I don’t have a lathe).
It looks like he cut 3/8” or less from the barrel’s OAL. I wouldn’t think that little would put us in this position but here we are…
The customer calls me up and says hey my gun stopped running. He brings it by and then I find out what happened. Long story short, this guy is a friend so I’m “stuck” fixing this mess.
So gun was ejecting way over gassed with the JP SCS and still not locking back so I dropped the upper on one of my lowers with Geissele Super 42 spring and H2 buffer and it worked better. It locked back occasionally and the ejection was about 4:00 so the bolt carrier speed definitely was slowed.
So customer wants to stay with the S42H2. Now we have to give the system more gas to lock back and be reliable. The question is how far we need to go.
I have gone up to 0.78” incrementally and still occasionally not locking back but ejection is moving forward to around 3:00 so the BCG is picking up some speed. All of this has been tested with the AGB fully “open” and unrestricted.
Is there a max for a barrel this short?
I had an old DD 10.3 barrel that had an 0.080” port so I didn’t want to go too much past that but…
SME help is greatly appreciated! Thanks in advance.
Carbine or Midlength gas system? I don't want to just assume Carbine. Also, final length of the barrel is 10"?
I'm not an SME, but this sheet may provide some ideas, until an SME can pop in.....
Documented Gas Port sizes (https://docs.google.com/spreadsheets/d/1tXunBDX5Gaz87BqxwNxDUlWNK9nEv-cZEQoLq2JXXrk/edit#gid=766121382)
Sparky5019
10-14-23, 14:26
Carbine gas system. I’ll check out that link. Thanks.
Looks like the shorter the gas system goes relative to barrel length the ports get significantly larger so that helps.
Anyone with experience. Please chime in here!
10.3" is on the razors edge of reliability in the first place. An adjustable gas block with never be as efficient as a fixed block as any adjustable mechanism can only ever hope to create a seal as good at something without an adjustable valve on it.
Sounds like he learned a valuable lesson to not alter a gun on the edge of reliability for the cosmetics of "less rail gap".
10.3"/10.5" dwell time is minimal in the first place, trying to chase reliability below that in barrel length is a waste of time if you ask me.
Go back to a .070"+/- a hair port size on a 10.3/10.5" barrel, a good sealing fixed gas block, and let the gun do what we know they can with known dimensions/ values. If the dude wants to argue about it, let him take it back to the guy who agreed to chop it down in the first place and let him deal with that mess.
Sparky5019
10-15-23, 07:50
10.3" is on the razors edge of reliability in the first place. An adjustable gas block with never be as efficient as a fixed block as any adjustable mechanism can only ever hope to create a seal as good at something without an adjustable valve on it.
Sounds like he learned a valuable lesson to not alter a gun on the edge of reliability for the cosmetics of "less rail gap".
10.3"/10.5" dwell time is minimal in the first place, trying to chase reliability below that in barrel length is a waste of time if you ask me.
Go back to a .070"+/- a hair port size on a 10.3/10.5" barrel, a good sealing fixed gas block, and let the gun do what we know they can with known dimensions/ values. If the dude wants to argue about it, let him take it back to the guy who agreed to chop it down in the first place and let him deal with that mess.
While I don’t disagree with you, I’m telling a friend to basically f*ck off and that type advice is not what I’m here to illicit. I do understand what optimal specs are…we are beyond that in this situation. Thank you for your opinion.
This thread is here so I can gain some insight on our SME’s EXPERIENCE and KNOWLEDGE of what is possible outside the optimal specs. I would appreciate as objective information as possible.
This is a shitty situation but not nearly as bad as a lot of the dumb shit I see guys post about they want to do to their own guns; cosmetic or not.
Thanks in advance for the help.
While I don’t disagree with you, I’m telling a friend to basically f*ck off and that type advice is not what I’m here to illicit. I do understand what optimal specs are…we are beyond that in this situation. Thank you for your opinion.
This thread is here so I can gain some insight on our SME’s EXPERIENCE and KNOWLEDGE of what is possible outside the optimal specs. I would appreciate as objective information as possible.
This is a shitty situation but not nearly as bad as a lot of the dumb shit I see guys post about they want to do to their own guns; cosmetic or not.
Thanks in advance for the help.
What do you think makes someone an SME on this topic?
Sparky5019
10-16-23, 04:53
What do you think makes someone an SME on this topic?
The admins have given them a profile title in yellow of “Subject Matter Expert”.
I respect that you have extensive knowledge given what you do for a living but I’m sorry, I will not be telling a friend to f*ck off buy a new upper because you did not ask questions. He learned from this experience and fixing his issue will solidify him as a future customer. I’m sure y’all have done the same thing.
Defaultmp3
10-16-23, 09:00
It looks like he cut 3/8” or less from the barrel’s OAL. I wouldn’t think that little would put us in this position but here we are…Perhaps the Geissele barrel had a swage, like some CHF barrels, and this was contributing to the gas drive, and with the chop, it was reduced, beyond just the issue of the further reduced dwell time.
So gun was ejecting way over gassed with the JP SCS and still not locking back so I dropped the upper on one of my lowers with Geissele Super 42 spring and H2 buffer and it worked better. It locked back occasionally and the ejection was about 4:00 so the bolt carrier speed definitely was slowed.Did you mean undergassed?
Is there a max for a barrel this short?
I had an old DD 10.3 barrel that had an 0.080” port so I didn’t want to go too much past that but…I don't see why you wouldn't. Gas port size is just one of many issues at play, there is also the size of the bore itself (I recall Amphibian over on ARFCOM doing some testing back in the day show differences in gas port sizing between two different barrels from the same manufacturer in order to get optimized performance with the exact same suppressor), ammunition, lubrication, etc.
The admins have given them a profile title in yellow of “Subject Matter Expert”.
I respect that you have extensive knowledge given what you do for a living but I’m sorry, I will not be telling a friend to f*ck off buy a new upper because you did not ask questions. He learned from this experience and fixing his issue will solidify him as a future customer. I’m sure y’all have done the same thing.Someone with the title Subject Matter Expert title here doesn't mean they're a SME on ARs. Pretty sure it really just means that they are/were verified SOF.
Sparky5019
10-16-23, 09:09
No it was over gassed. BCG moving super fast and brass going forward but would still not lock back with the JP SCS.
Point about SMEs. I just want solid objective info that doesn’t involve telling a friend to f*ck off and judge the guy for making a mistake. I’m here to fix the problem for him and help him learn from it.
Thanks!!
Defaultmp3
10-16-23, 09:28
No it was over gassed. BCG moving super fast and brass going forward but would still not lock back with the JP SCS.I'm confused, what combination exactly is overgassed, then? The structure of you post implies that the rifle was overgassed with the JP SCS prior to you opening up the gas port; what was the gas port size when you decided that it was overgassed with the JP SCS?
Sparky5019
10-16-23, 09:38
It was over gassed with the JP SCS when suppressed especially. At that point the port had not been altered. The barrel had been shortened at that point.
Once I got the S42H2 in it, then it began to act more “normal” and be under gassed (unsuppressed) which would be consistent with shortening the swell time by cutting the barrel.
We know it needs more gas, the million dollar question is how much more. Lol
No it was over gassed. BCG moving super fast and brass going forward but would still not lock back with the JP SCS.
Point about SMEs. I just want solid objective info that doesn’t involve telling a friend to f*ck off and judge the guy for making a mistake. I’m here to fix the problem for him and help him learn from it.
Thanks!!
Well, I literally just spent the last two weekends teaching our Armorers Course to students, and wrote most of the slides we use on dwell time and port sizing…
I don’t know why you seem to think that telling someone that they’ve made a mistake that can not be reliably corrected is telling them to piss off. Part of being trusted in your field is knowing when to tell people no to a bad idea.
It’s highly unlikely that you’ll find a way to make this reduced length barrel reliable now, and simply replacing the barrel and gas block with known quantity items is likely the most cost effective, time effective, and reliable resolution to your “friends” woes. If 5.56mm NATO carbine gas length barrels were viable below 10.3”, I think you’d be seeing at least a couple of them floating around. That you don’t is a clue. You’ll be in experimental territory trying to force this thing to run, with what will likely be an extremely narrow window of circumstances under which it’ll actually work.
Alternatively you could fix this problem tomorrow and give this dude a highly reliable upper again… with a 10.3” barrel setup that’s already been proven to work in every corner of the world.
Sparky5019
10-16-23, 10:16
Well, I literally just spent the last two weekends teaching our Armorers Course to students, and wrote most of the slides we use on dwell time and port sizing…
I don’t know why you seem to think that telling someone that they’ve made a mistake that can not be reliably corrected is telling them to piss off. Part of being trusted in your field is knowing when to tell people no to a bad idea.
It’s highly unlikely that you’ll find a way to make this reduced length barrel reliable now, and simply replacing the barrel and gas block with known quantity items is likely the most cost effective, time effective, and reliable resolution to your “friends” woes. If 5.56mm NATO carbine gas length barrels were viable below 10.3”, I think you’d be seeing at least a couple of them floating around. That you don’t is a clue. You’ll be in experimental territory trying to force this thing to run, with what will likely be an extremely narrow window of circumstances under which it’ll actually work.
Alternatively you could fix this problem tomorrow and give this dude a highly reliable upper again… with a 10.3” barrel setup that’s already been proven to work in every corner of the world.
Dude. He was told he made a mistake. He gets it. I stated that. Literally all you offered was telling him he was wrong and to replace the system.
How about share some knowledge from all those slides about porting and dwell times so the community can take something away from this.
I don’t know why you seem to think that telling someone that they’ve made a mistake that can not be reliably corrected is telling them to piss off. Part of being trusted in your field is knowing when to tell people no to a bad idea.
+1 to this!
Sparky5019
10-16-23, 15:03
+1 to this!
That’s not strictly what I said. What I said was he’s been told that. He gets it. We’re past that. I refused to tell him too bad I can’t help you. I was looking for some objective technical information that would help us work with what we have.
Looks like I’m shit outta luck.
That’s not strictly what I said. What I said was he’s been told that. He gets it. We’re past that. I refused to tell him too bad I can’t help you. I was looking for some objective technical information that would help us work with what we have.
You wrote:
I respect that you have extensive knowledge given what you do for a living but I’m sorry, I will not be telling a friend to f*ck off buy a new upper because you did not ask questions. He learned from this experience and fixing his issue will solidify him as a future customer. I’m sure y’all have done the same thing.
Jim D's response which I quoted is a logical reply to this. It is not "telling him to f*ck off" to inform him that the barrel cannot be economically resuscitated to a reliable condition. It is your choice to cast it that way.
Sparky5019
10-16-23, 16:04
You wrote:
Jim D's response which I quoted is a logical reply to this. It is not "telling him to f*ck off" to inform him that the barrel cannot be economically resuscitated to a reliable condition. It is your choice to cast it that way.
Fair enough. The tone and intended meaning that I took from his post was tell him he made a mistake and to start over. There was no further assistance given or support for his opinion that one could not make a 10” barrel reliable.
I addressed the fact that he had been told and he acknowledged that he’d made a mistake. We then set to the task of attempting to properly open the gas port to make the barrel reliable within his parameters. That was my question to everyone here.
I’m sorry but I do not accept an answer of “just buy a new barrel” without some objective supporting data as an acceptable answer.
This is a technical sub forum. I’m looking for technical data.
I’m sorry I don’t fall into the “just scrap it and buy a new one” crowd.
I was searching for experience that people had experience with different sizes of ports and maybe some dwell time thoughts.
If it matters to anyone at this point…
The port is at 0.078” currently and the barrel is gaining unsuppressed reliability as it is locking back on the S42H2 with several different types of ammo.
Not everything in life can be un-F’d, no matter how much you want that to be. Also see sunk cost fallacy.
Tell him it’s X dollars to replace the barrel, or X dollars per hour for you to mess with it.
I would stop chasing the gas port and figure out what else might be causing the problem before drilling any more. Check the gas tube, try a regular gas block, swap in a known good BCG, check for hammer drag…
I used to make AR barrels for a living and never had any occasion to try to make a 10” run. I doubt there is SME who can give you the right gas port size.
Sparky5019
10-16-23, 16:48
Not everything in life can be un-F’d, no matter how much you want that to be. Also see sunk cost fallacy.
Tell him it’s X dollars to replace the barrel, or X dollars per hour for you to mess with it.
I would stop chasing the gas port and figure out what else might be causing the problem before drilling any more. Check the gas tube, try a regular gas block, swap in a known good BCG, check for hammer drag…
I used to make AR barrels for a living and never had any occasion to try to make a 10” run. I doubt there is SME who can give you the right gas port size.
Thanks for the info.
Everything otherwise is in good working order. We’ve had the cost discussion; I’m not concerned about that at this point.
I was thinking that 1/4” of length wouldn’t be that difficult to compensate for in port size.
Does anyone have data on what pressure loss that 1/4” might account for?
IIRC the port pressure for a carbine length has system was something like 15k psi. I can’t recall but I read it on here years ago.
One item that is significantly reduced with very short power time (dwell time) configurations is the ability to function well suppressed and un-suppressed without any other changes.
Drilling out the port without any idea of what size it should be for a given configuration is not recommended.
It is now larger than anyone would have recommended, so don't do any more of that.
The upper may be able to run suppressed and un-suppressed by swapping out the extra strong S42 and or H2 buffer for something normal.
The AGB should be dialed down when the suppressor is attached.
Sparky5019
10-16-23, 16:56
One item that is significantly reduced with very short power time (dwell time) configurations is the ability to function well suppressed and un-suppressed without any other changes.
Drilling out the port without any idea of what size it should be for a given configuration is not recommended.
It is now larger than anyone would have recommended, so don't do any more of that.
The upper may be able to run suppressed and un-suppressed by swapping out the extra strong S42 and or H2 buffer for something normal.
The AGB should be dialed down when the suppressor is attached.
The initial plan was get it reliable unsuppressed then allow the AGB to be adjusted slightly when suppressed.
Would you recommend dropping to an H buffer or dropping to a mil spec spring or both? I typically favor dropping oscillating mass before reducing spring pressure but…
This is the type of info I was looking for. THANK YOU!
Someone with the title Subject Matter Expert title here doesn't mean they're a SME on ARs. Pretty sure it really just means that they are/were verified SOF.
I’m not sure they even do that anymore. I asked about it two years ago and never received a reply. Then I noticed that almost no one had it anymore.
Edit: at that time, I discussed this with ST911, and he explained the thing, and told me to contact username: STAFF . STAFF is who did not reply.
I’m sorry but I do not accept an answer of “just buy a new barrel” without some objective supporting data as an acceptable answer.
This is a technical sub forum. I’m looking for technical data.
Fair enough. :-)
Sparky5019
10-16-23, 18:43
I’m not sure they even do that anymore. I asked about it two years ago and never received a reply. Then I noticed that almost no one had it anymore.
They may not. To be fair my interactions with them years ago were in hyper technical discussions so I may have formed the wrong impression. lol
Clint is definitely an expert on this exact topic and we’ve had similar discussions in years past.
I’m not sure they even do that anymore. I asked about it two years ago and never received a reply. Then I noticed that almost no one had it anymore.
There are a few of us around still. We are all verified SOF. Most have left and I know the last guy to get added. and that was a very long time ago. There are two reasons for this.
1. the MOD that was actually able to Vet people no longer is here.
2. Most of us do not post much as a bunch of retards love to argue about sh!t they know nothing about, and that gets old real quick.
OP: Just take the hit and get a new barrel. With all of the stuff done to it at a minimum the barrel harmonics are trashed. Unless, it is just a range toy, then keep messing with it and have fun.
Sparky5019
10-17-23, 07:25
There are a few of us around still. We are all verified SOF. Most have left and I know the last guy to get added. and that was a very long time ago. There are two reasons for this.
1. the MOD that was actually able to Vet people no longer is here.
2. Most of us do not post much as a bunch of retards love to argue about sh!t they know nothing about, and that gets old real quick.
OP: Just take the hit and get a new barrel. With all of the stuff done to it at a minimum the barrel harmonics are trashed. Unless, it is just a range toy, then keep messing with it and have fun.
1. Copy that. Thanks.
2. Agreed and I appreciate the info.
We may still get a new barrel but after ADCO recrowned it, it groups better at 50 that before so we’ll play for a bit and see. If the groups had opened up, I’d have shit canned it already but since they got better, we figured it was worth the attempt. Lol
There are a few of us around still. We are all verified SOF. Most have left and I know the last guy to get added. and that was a very long time ago. There are two reasons for this.
1. the MOD that was actually able to Vet people no longer is here.
2. Most of us do not post much as a bunch of retards love to argue about sh!t they know nothing about, and that gets old real quick.
OP: Just take the hit and get a new barrel. With all of the stuff done to it at a minimum the barrel harmonics are trashed. Unless, it is just a range toy, then keep messing with it and have fun.
1. The .mil provides piles of documentation that’d be easy to redact a bit and use for vetting. But I guess a suitable nerd could make a convincing forgery.
2. That’s actually the only reason I was interested in getting the SME thing here. Dudes that want to argue shit because they took a two day class and wore armor once for fun. Then some poor dude lands on that page via internet search and gets bad advice because he can’t tell who is who. “That dude says he went to a class and deltas (lololol) said this, so it must be right”.
1. The .mil provides piles of documentation that’d be easy to redact a bit and use for vetting. But I guess a suitable nerd could make a convincing forgery.
2. That’s actually the only reason I was interested in getting the SME thing here. Dudes that want to argue shit because they took a two day class and wore armor once for fun. Then some poor dude lands on that page via internet search and gets bad advice because he can’t tell who is who. “That dude says he went to a class and deltas (lololol) said this, so it must be right”.
Based on a conversation I had with other people it can be faked very easily....... All of our Como prior to getting vetted was via my SOC.MIL email account.
Sparky5019
10-17-23, 08:10
1. The .mil provides piles of documentation that’d be easy to redact a bit and use for vetting. But I guess a suitable nerd could make a convincing forgery.
2. That’s actually the only reason I was interested in getting the SME thing here. Dudes that want to argue shit because they took a two day class and wore armor once for fun. Then some poor dude lands on that page via internet search and gets bad advice because he can’t tell who is who. “That dude says he went to a class and deltas (lololol) said this, so it must be right”.
Gospel.
Based on a conversation I had with other people it can be faked very easily....... All of our Como prior to getting vetted was via my SOC.MIL email account. Fair enough. I think for the most part, we know who’s legit around here. Its usually pretty obvious to anyone that knows. Unfortunately, with the flight of SMEs from here, I think fewer and fewer new members will come here for the signal/noise ratio* and hands-on expertise this site was once known for, and we’re looking at a culture shift in this circle.
*ironically, I’m polluting that a bit right now, but there is a reason I haven’t moved this convo to IM or text. And that reason is transparency.
Sparky5019
10-17-23, 08:21
Based on a conversation I had with other people it can be faked very easily....... All of our Como prior to getting vetted was via my SOC.MIL email account.
That’s good info.
Honestly there’s too many people out there who their because they are in “the industry” that think that they either are or should be SMEs. JMHO, but what actually makes one an expert is knowing that there is always more to know and understand and that they themselves do not know it all.
I do appreciate everyone’s input on this. Even the ones I have disagreed with.
I’ll do some work and test firing and report back later this week or this weekend with the results.
jackblack73
10-17-23, 09:23
Your buddy made a dumb mistake cutting his barrel for aesthetics. Choosing to open the gas port more just so he could stick with an S42H2 seems equally dumb to me.
Legit SMEs leaving here and Alias scamming a bunch of instructors and collapsing were both major hits IMO. I actually got an infraction for responding to a SME thread a long time ago since I didn’t realize they were the only one that could respond. Atypical for sure but a neat concept, despite the fact that I’ve publicly disagreed with at least two other SMEs.
We also used to have labeled industry professionals too IIRC, so both in one thread could provide a lot of real info. RIP to when we really focused on shooting.
Sent from my iPhone using Tapatalk Pro
Sparky5019
10-17-23, 11:40
Legit SMEs leaving here and Alias scamming a bunch of instructors and collapsing were both major hits IMO. I actually got an infraction for responding to a SME thread a long time ago since I didn’t realize they were the only one that could respond. Atypical for sure but a neat concept, despite the fact that I’ve publicly disagreed with at least two other SMEs.
We also used to have labeled industry professionals too IIRC, so both in one thread could provide a lot of real info. RIP to when we really focused on shooting.
Sent from my iPhone using Tapatalk Pro
I remember the industry pro title. I’m seeing that most forums are ending like fb groups now just bickering and no objective discussion around facts and data. It’s unfortunate because there were some really great discussions here that we all came out better knowing more. Now it’s just bickering. Sad.
Fair enough. The tone and intended meaning that I took from his post was tell him he made a mistake and to start over. There was no further assistance given or support for his opinion that one could not make a 10” barrel reliable.
I addressed the fact that he had been told and he acknowledged that he’d made a mistake. We then set to the task of attempting to properly open the gas port to make the barrel reliable within his parameters. That was my question to everyone here.
I’m sorry but I do not accept an answer of “just buy a new barrel” without some objective supporting data as an acceptable answer.
This is a technical sub forum. I’m looking for technical data.
I’m sorry I don’t fall into the “just scrap it and buy a new one” crowd.
I was searching for experience that people had experience with different sizes of ports and maybe some dwell time thoughts.
If it matters to anyone at this point…
The port is at 0.078” currently and the barrel is gaining unsuppressed reliability as it is locking back on the S42H2 with several different types of ammo.
I don't know how else to put this but can you point to a single sub-10.3" 5.56mm barrel, with a carbine length gas system, from a manufacturer you trust or recommend?
BCM doesn't even offer 10.3/10.5" at all, and starts at 11.5".
There's mountains of data out there on how 10.3" works... and most everyone with any measure of experience in making reliable SBR's will advise to go 11.5" if there's any way possible to do so.
You've got about 2.75" of dwell on a 10.5" rifle... and something like .4" of that was removed. Side note, but it really makes me wonder what process they used to cut the new threads since the threads on that barrel were .6".
Roughly 15% of the dwell was robbed from a system that quality manufacturers try not to even do unless they have to... you're literally on an island now for data. No one has figured out how to make the gun run with so little dwell. You're not getting technical data or numbers to try because there isn't any, no one wants to do this. Those of us who understand how critical dwell is are seeing the writing on the wall here. You've already added about 25% more gas than it had before and it's still not enough to compensate for the ~15% reduction in dwell.
If you're able to get this thing to run at all, it's going to be recoiling excessively hard, and be one of the pickiest eaters of any upper you can imagine. The cost of test fire ammo, labor, and new components is going to eclipse a barrel/gas block swap by a lot. In the end the product he'll end up with is going to be incredibly high maintenance, and be highly sensitive to component wear with respect to reliability. You can expect accelerated wear on gas rings, action spring, extractor and extractor spring, hammer pin, bolt catch, bolt and cam pin, and the upper receiver at the cam pin track.
Things like ejector spring condition, extractor condition, magazine spring condition and gas ring condition could shut down reliable operation (if it's ever established) since your margins for errors are going to be so slim.
What you're trying to do is fight against all of this to try and pioneer reliable function in a system with less dwell than anyone who does this professionally would probably ever agree to attempt for someone.
Practically speaking, cutting bait and starting over is in everyone's interest.
Sparky5019
10-17-23, 15:25
I don't know how else to put this but can you point to a single sub-10.3" 5.56mm barrel, with a carbine length gas system, from a manufacturer you trust or recommend?
BCM doesn't even offer 10.3/10.5" at all, and starts at 11.5".
There's mountains of data out there on how 10.3" works... and most everyone with any measure of experience in making reliable SBR's will advise to go 11.5" if there's any way possible to do so.
You've got about 2.75" of dwell on a 10.5" rifle... and something like .4" of that was removed. Side note, but it really makes me wonder what process they used to cut the new threads since the threads on that barrel were .6".
Roughly 15% of the dwell was robbed from a system that quality manufacturers try not to even do unless they have to... you're literally on an island now for data. No one has figured out how to make the gun run with so little dwell. You're not getting technical data or numbers to try because there isn't any, no one wants to do this. Those of us who understand how critical dwell is are seeing the writing on the wall here. You've already added about 25% more gas than it had before and it's still not enough to compensate for the ~15% reduction in dwell.
If you're able to get this thing to run at all, it's going to be recoiling excessively hard, and be one of the pickiest eaters of any upper you can imagine. The cost of test fire ammo, labor, and new components is going to eclipse a barrel/gas block swap by a lot. In the end the product he'll end up with is going to be incredibly high maintenance, and be highly sensitive to component wear with respect to reliability. You can expect accelerated wear on gas rings, action spring, extractor and extractor spring, hammer pin, bolt catch, bolt and cam pin, and the upper receiver at the cam pin track.
Things like ejector spring condition, extractor condition, magazine spring condition and gas ring condition could shut down reliable operation (if it's ever established) since your margins for errors are going to be so slim.
What you're trying to do is fight against all of this to try and pioneer reliable function in a system with less dwell than anyone who does this professionally would probably ever agree to attempt for someone.
Practically speaking, cutting bait and starting over is in everyone's interest.
What do you want me to say? You’re right? Then…YOU ARE RIGHT. Happy?
I disagree with because you did not answer my initial questions not because your point is not valid. As I told before, he has been told of his error he gets it and he wanted to see if it could be made to work. What he paid the other guy or me is not part of this discussion. The above info is valid and we are all aware of it. I appreciate you giving some data on the reliability of the 10.5/10.3.
This guy is a good shooter and he cares very little about a minor increase in recoil.
Not sure why your head is exploding over what someone else wants to do. When I built this upper group we had the discussion and he is very educated on all the above info. He and I agreed on that. All the components are currently serviceable and in excellent shape. Of course we’ll be watching the wear patterns going forward and will replace the barrel when we start seeing issues. I may even order one for him shortly just to have on hand but that has no bearing on the original question that was asked and that was seeking technical data.
Defaultmp3
10-17-23, 15:37
I'm just confused at how the gun becomes overgassed after a barrel chop, and to the extent that it's outrunning the magazine spring for locking back. Conventional wisdom would dictate that it would become undergassed, no?
If he wants to keep the barrel, a muzzle booster (i.e. Noveske KX3) should help restore some needed back pressure.
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I'm just confused at how the gun becomes overgassed after a barrel chop, and to the extent that it's outrunning the magazine spring for locking back. Conventional wisdom would dictate that it would become undergassed, no?
Ports have to get opened to compensate for the dwell reduction. 10.5" suppressed is always fast/ gassy/ violent... now even more so.
Sparky5019
10-17-23, 15:44
If he wants to keep the barrel, a muzzle booster (i.e. Noveske KX3) should help restore some needed back pressure.
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He’ll shoot it suppressed with an RC2 most of the time that’s stated in the OP.
jackblack73
10-17-23, 16:27
I'm just confused at how the gun becomes overgassed after a barrel chop, and to the extent that it's outrunning the magazine spring for locking back. Conventional wisdom would dictate that it would become undergassed, no?
He already opened the port up from 0.069 to 0.078.
Sparky5019
10-17-23, 16:47
I'm just confused at how the gun becomes overgassed after a barrel chop, and to the extent that it's outrunning the magazine spring for locking back. Conventional wisdom would dictate that it would become undergassed, no?
It was overgassed with his JP SCS. That unit had 1000s of rounds on it and was worn TF out.
Sparky5019
10-17-23, 16:47
He already opened the port up from 0.069 to 0.078.
Incorrect at that point. See above.
Defaultmp3
10-17-23, 16:50
Ports have to get opened to compensate for the dwell reduction. 10.5" suppressed is always fast/ gassy/ violent... now even more so.
He already opened the port up from 0.069 to 0.078.My remark was specifically in context of the fact that it was stated that the gun was overgassed with only the barrel chop, without opening up the port any, when it had previously been normally gassed prior to the barrel chop. The port was only opened up after it was established at the gun was not locking back consistently with both the JP SCS and the Geissele Super 42 with an H2.
It was overgassed with his JP SCS. That unit had 1000s of rounds on it and was worn TF out.Are you saying that it was overgassed and failing to lock back on an empty mag prior to the chop, too, given that the SCS would also be worn out by then? Again, it doesn't make any sense to me that the gun would become overgassed with only the barrel chop, and all other things being equal.
Sparky5019
10-17-23, 17:03
My remark was specifically in context of the fact that it was stated that the gun was overgassed with only the barrel chop, without opening up the port any, when it had previously been normally gassed prior to the barrel chop. The port was only opened up after it was established at the gun was not locking back consistently with both the JP SCS and the Geissele Super 42 with an H2.
Are you saying that it was overgassed and failing to lock back on an empty mag prior to the chop, too, given that the SCS would also be worn out by then? Again, it doesn't make any sense to me that the gun would become overgassed with only the barrel chop, and all other things being equal.
This has all been explained but…
Gun ran fine. See parts list in the OP. Barrel was cut by ~1/4”. Failed to lock back suppressed on the afore mentioned JP SCS but the BCG was moving very fast and ejecting at 1:30-2:00. Switched to S42H2 and things calmed to be “under gassed” and ejecting at 3:00. Not locking back unsuppressed. Begin port work and testing unsuppressed. As more gas drive was added, ejection moved further forward. Now ejecting at 3:00 and occasionally locking back on S42H2.
Will probably drop to an H and see how things are from there. There are the Cliff Notes and everyone is up to speed.
He’ll shoot it suppressed with an RC2 most of the time that’s stated in the OP.
In case you guys haven't already considered it, that barrel is probably right on the line of minimum barrel length for the RC2. I don't know how much it'll matter because it'd be close, but worth noting.
Sparky5019
10-17-23, 17:58
In case you guys haven't already considered it, that barrel is probably right on the line of minimum barrel length for the RC2. I don't know how much it'll matter because it'd be close, but worth noting.
Yeah. We know. Given how the barrel shoots at 50 I think the rounds are stabilizing ok at this point. If it degrades, we’ll replace it so he doesn’t get a baffle strike or have any other issues.
BufordTJustice
10-19-23, 21:25
Not everything in life can be un-F’d, no matter how much you want that to be. Also see sunk cost fallacy.
Tell him it’s X dollars to replace the barrel, or X dollars per hour for you to mess with it.
THIS. I have had to tell friends this difficult thing: "You f'd up. I can't fix it. The end."
I actually have a friend chasing an unrelated, but just-as-silly goal of trying to convert his FNH-made PSA 10.3" FSB upper with A2 HG's into a free-floated setup with an AGB or a BRT EZ-tune gas tube.
-Want a superb Centurion FSB-cutout FF handguard? Nope.
-Want to shave your FSB? Nope.
-Want to swap gas tubes for a BRT EZ-Tune? Nope.
-Want to buy a new barrel that is designed for a lo-pro GB? Nope.
-Want to just sell this upper and buy one that isn't a pos PSA? Nope.
So, you know what I did? I stopped helping him. Told him to get a known-quality barrel like Sionics, BCM, LMT, SOLGW; a known quality GB and HG, etc....or to just BUY a known good upper. He told me that this "was a waste". I told him that my time (and his) was more valuable than this low-ROI effort and my diagnostic efforts were now concluded.
You know what? We are still very close friends. We don't discuss it....which is great, because IDGAF. He knows his clear path to success. He makes plenty of money....whenever he gets emotionally motivated enough to stop F-ing around and just do it right, he knows who to call.
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THIS. I have had to tell friends this difficult thing: "You f'd up. I can't fix it. The end."
I actually have a friend chasing an unrelated, but just-as-silly goal of trying to convert his FNH-made PSA 10.3" FSB upper with A2 HG's into a free-floated setup with an AGB or a BRT EZ-tune gas tube.
-Want a superb Centurion FSB-cutout FF handguard? Nope.
-Want to shave your FSB? Nope.
-Want to swap gas tubes for a BRT EZ-Tune? Nope.
-Want to buy a new barrel that is designed for a lo-pro GB? Nope.
-Want to just sell this upper and buy one that isn't a pos PSA? Nope.
So, you know what I did? I stopped helping him. Told him to get a known-quality barrel like Sionics, BCM, LMT, SOLGW; a known quality GB and HG, etc....or to just BUY a known good upper. He told me that this "was a waste". I told him that my time (and his) was more valuable than this low-ROI effort and my diagnostic efforts were now concluded.
You know what? We are still very close friends. We don't discuss it....which is great, because IDGAF. He knows his clear path to success. He makes plenty of money....whenever he gets emotionally motivated enough to stop F-ing around and just do it right, he knows who to call.
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We all have that one buddy. Mine has O-Lights on his DD rifles.
BufordTJustice
10-20-23, 11:27
We all have that one buddy. Mine has O-Lights on his DD rifles.
Do we have the same buddy? lol.
He has a bone stock DD M4v7 with an Olight. Hhahahahahaha
Like I said, he's not poor....he's STUBBORN.
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titsonritz
10-22-23, 22:11
THIS. I have had to tell friends this difficult thing: "You f'd up. I can't fix it. The end."
I actually have a friend chasing an unrelated, but just-as-silly goal of trying to convert his FNH-made PSA 10.3" FSB upper with A2 HG's into a free-floated setup with an AGB or a BRT EZ-tune gas tube.
-Want a superb Centurion FSB-cutout FF handguard? Nope.
-Want to shave your FSB? Nope.
-Want to swap gas tubes for a BRT EZ-Tune? Nope.
-Want to buy a new barrel that is designed for a lo-pro GB? Nope.
-Want to just sell this upper and buy one that isn't a pos PSA? Nope.
So, you know what I did? I stopped helping him. Told him to get a known-quality barrel like Sionics, BCM, LMT, SOLGW; a known quality GB and HG, etc....or to just BUY a known good upper. He told me that this "was a waste". I told him that my time (and his) was more valuable than this low-ROI effort and my diagnostic efforts were now concluded.
You know what? We are still very close friends. We don't discuss it....which is great, because IDGAF. He knows his clear path to success. He makes plenty of money....whenever he gets emotionally motivated enough to stop F-ing around and just do it right, he knows who to call.
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Absolutely, I have a good friend that I told I would not build guns for him because of the dog shit parts he buys. I’ll let him use my tools and I’ll stand and watch him but I won’t wrench on it. I told him the only way I’ll build a gun for him is if he buys the parts I tell him to buy.
Absolutely, I have a good friend that I told I would not build guns for him because of the dog shit parts he buys. I’ll let him use my tools and I’ll stand and watch him but I won’t wrench on it. I told him the only way I’ll build a gun for him is if he buys the parts I tell him to buy.
I had a neighbor ask me to help he and his brother build several ARs for them and their boys. They gave me a budget and I gave them a parts list of decent, quality parts to buy (with options and explanations.) They pretty much ignored my advice and bought the cheapest shit they could find. When they asked me to help them put it all together I politely declined.
BufordTJustice
10-23-23, 16:05
I had a neighbor ask me to help he and his brother build several ARs for them and their boys. They gave me a budget and I gave them a parts list of decent, quality parts to buy (with options and explanations.) They pretty much ignored my advice and bought the cheapest shit they could find. When they asked me to help them put it all together I politely declined.
Yep.
So many people mistakenly think that good advice scales. "I'll just do 80% of what this smart guy said, and I'll get 80% of the results!"
People who are dumb enough to believe that advice scales are *slow learners*; it's honestly better for them to learn the hard/expensive way once you've made a single good faith attempt to educate them.
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