View Full Version : 11.5" Barrel Optimum Gas Port Size
Is there any data that even suggests an optimum size?
It seems companies are mostly unwilling to even share these specs...
With many shooters reporting over gassing issues it seems like the metrics companies are using to determine gas port size have more to do with ensuring cycling instead of actually determining optimum performance.
Bob Sacamano
07-25-18, 06:36
Port size is a critical spec and should be disclosed. For a 10.5” carbine gas, .070” is “the standard”. 11.5” should be slightly smaller. I am not aware of any 11.5 barrels with a port smaller than .070”. Iirc, Colt sells a .070” 11.5” and Sionics sells their RGP barrel with a .071” port.
Either would be good choices to start. Order a few BRT ports then work down in size until you are happy.
https://www.m4carbine.net/showthread.php?197085-Gas-Port-Data
I have a Colt 11.5" upper with a .063" BRT Micro Port. It locks back without a suppressor.
Is there any data that even suggests an optimum size?
Unsuppressed: .070" would be pretty good.
Suppressed: I'd probably run .063-.065"... I don't think my .063" 11.5 would lock back without the can unless I shot some smoking hot Black Hills 5.56 ammo. Anything weaker, and I was starting to lose reliability.
I've got a Triarc barrel with a .055" port that will cycle XM193 but not lock back on empty. Runs perfect with a can (Saker 556 and Sandman-K).
Jwknutson17
07-25-18, 11:20
You will be fine in the low .062-4 range on an 11.5 with quality ammo, Auto carrier, and an A5H2.
.070/1 is too large for any suppressed only application.
I also have a 11.0 barrel with .0625 and it cycles with an H3 carbine spring, and also with an A5H3 Colt spring unsuppressed with m193 and mk262s. Doesn't lock back about half the time on empty mag unsuppressed.
.070/1 is too large for any suppressed only application.
It's pure heaven unsuppressed though. That's my house gun.
And here I thought we were all talking about our new BRT 11.5" OPTIMUM CQB Barrel (http://www.blackrivertactical.com/concrete5/store/#!/BRT-11-5-OPTIMUM-CQB-Barrel/p/110110072/category=1852006)
https://dqzrr9k4bjpzk.cloudfront.net/images/812059/855364694.jpg (https://www.blackrivertactical.com/concrete5/store/#!/BRT-11-5-OPTIMUM-CQB-Barrel/p/110110072/category=1852006)
Furbyballer
07-25-18, 13:16
And here I thought we were all talking about our new BRT 11.5" OPTIMUM CQB Barrel (http://www.blackrivertactical.com/concrete5/store/#!/BRT-11-5-OPTIMUM-CQB-Barrel/p/110110072/category=1852006)
https://dqzrr9k4bjpzk.cloudfront.net/images/812059/855364694.jpgGas port size? Why is this threaded for a 30 cal can and not a 556? When will it be available?
Sent from my SM-G950U using Tapatalk
Bob Sacamano
07-25-18, 15:20
Looks good Clint. I see you have a standard and a suppressed option. What are ports for each? Wish they were 1/2-28. Its easy to get someone to recut 5/8-24 to 1/2-28 on SS, not sure on the QPQ.
Looks like these will be compatable with a standard FSB?
Is there any data that even suggests an optimum size?
Every barrel length has an Optimum gas system length and every combination has an Optimum gas port size.
11.5" carbine happens to be one of those OPTIMUM configurations.
Availability in the fall.
Yes on FSB compatibility.
The port sizes aren't set until final testing, but we expect they'll likely be in the high .06x for the standard and low .06x for the suppressor version.
Rest assured they'll NOT be over gassed.
The larger threads are to make the barrel stronger and more accurate.
1/2-28 threads leave very little meat at the critical muzzle crown.
These two M4C threads cover most of the discussion.
https://www.m4carbine.net/showthread.php?205786-5-8x24-threads-on-5-56-223
https://www.m4carbine.net/showthread.php?205690-Taper-Shoulder-Barrels
https://dqzrr9k4bjpzk.cloudfront.net/images/812059/628419704.jpg
Every barrel length has an Optimum gas system length and every combination has an Optimum gas port size.
11.5" carbine happens to be one of those OPTIMUM configurations.
Availability in the fall.
Yes on FSB compatibility.
The port sizes aren't set until final testing, but we expect they'll likely be in the high .06x for the standard and low .06x for the suppressor version.
Rest assured they'll NOT be over gassed.
The larger threads are to make the barrel stronger and more accurate.
1/2-28 threads leave very little meat at the critical muzzle crown.
These two M4C threads cover most of the discussion.
https://www.m4carbine.net/showthread.php?205786-5-8x24-threads-on-5-56-223
https://www.m4carbine.net/showthread.php?205690-Taper-Shoulder-Barrels
https://dqzrr9k4bjpzk.cloudfront.net/images/812059/628419704.jpg
Very interesting!
1. What is the criteria for optimum? Reliability to cycle properly, ejection, recoil impulse, mitigate barrel erosion and bolt wear, etc.
2. How is the testing done? Do start with a particular barrel and gas port size and incrementally go smaller while capturing data?
OPTIMUM gas drive starts with matching the gas system length with the barrel length for the cartridge pressure curve to maintain timing ratios in a certain range within the limits of available gas drive.
This is capped off with the final port sizing, with the objective being the widest operational envelope, lowest stress and soft recoil impulse.
More discussion in the mega thread.
https://www.m4carbine.net/showthread.php?189677-BRT-16-quot-OPTIMUM-Barrel-w-Extended-Length-Gas-System
Very interesting!
1. What is the criteria for optimum? Reliability to cycle properly, ejection, recoil impulse, mitigate barrel erosion and bolt wear, etc.
2. How is the testing done? Do start with a particular barrel and gas port size and incrementally go smaller while capturing data?
OPTIMUM gas drive starts with matching the gas system length with the barrel length for the cartridge pressure curve to maintain timing ratios in a certain range within the limits of available gas drive.
This is capped off with the final port sizing, with the objective being the widest operational envelope, lowest stress and soft recoil impulse.
More discussion in the mega thread.
https://www.m4carbine.net/showthread.php?189677-BRT-16-quot-OPTIMUM-Barrel-w-Extended-Length-Gas-System
Sooo...when will we get the 10.3? Lol
Sent from my iPhone using Tapatalk Pro
Sooo...when will we get the 10.3? Lol
Sent from my iPhone using Tapatalk Pro
.....ported for dedicated suppressor use.
Furbyballer
07-26-18, 06:54
Clint, are you going to tune your barrel to a specific 556 load and suppressor? I would be interested to know which 30 cal cans you use in your testing and which performs the best with your barrel. As of now, I can't think of any dedicated 556 cans off the top of my head that use 5/8 x 24 threads.
The Griffin M4SD series of 5.56 suppressors will attach to the muzzle devices in 5/8 x 24. I'm not sure about other manufacturers.
A 30 cal can on an SBR has some appeal. I like the idea of extra baffle diameter for reduced risk of baffle strikes and reduced back pressure.
The Suppressor Gas Drive barrels will be setup for normal function with 7.62 suppressors, which tend to be lower back pressure.
Cycling will speed up a bit if used with higher back pressure 5.56 suppressors, but should still be in a good range.
Clint, are you going to tune your barrel to a specific 556 load and suppressor? I would be interested to know which 30 cal cans you use in your testing and which performs the best with your barrel. As of now, I can't think of any dedicated 556 cans off the top of my head that use 5/8 x 24 threads.
snackgunner
07-26-18, 20:40
Clint would the aac 7.62-sdn-6 suppressor work with this barrel?
Edit : Im reading 5/8x24 i think thats what the 51t 7.62 mount thread is so should be good I think
I like this. I have a sdn6 but dont use it for anything since i dont have any rifle caliber but 5.56 since Im poor. Will go with one of these barrels then
Yes, just about any 7.62 suppressor with a 5/8-24 mount will work.
There are a lot of good 30 cal suppressors available these days.
Q
Sig
SilencerCo
Rugged
Dead Air
AAC
Griffin
These are all suitable, especially in the shorter lighter versions geared towards 300 BLK applications.
A large portion of the innovation in the suppressor industry is currently centered around 30 cal applications.
There are several 5.56 suppressors that have 5/8-24 QD mounts available for them.
The 5/8-24 AAC 51T mount works with the M4-2000, 556-SD and Mini-4.
The 5/8-24 SilencerCo ASR Mount works with the Specwar 556, Specwar 556K, Saker 556, Saker 556K.
The 5/8-24 Griffin Taper mount works with the Reece 5 and Optimus Micro w/ optional taper mount interface.
There may be others.
In addition, several of the modular 7.62 suppressors have dedicated 5.56 End Caps available.
-Rugged Surge, Razor, Micro30 End Cap
-SiCo Saker, Omega, Hybrid End Cap
-DeadAir Sandman End Cap
-Griffin Optimus End Cap
I just dont understand eliminating a ton of suppressors for the sake of something that's never been shown to be an issue except in theory or extremis (torquing muzzle devices to 100#, etc)
I just dont understand eliminating a ton of suppressors for the sake of something that's never been shown to be an issue except in theory or extremis (torquing muzzle devices to 100#, etc)
There's a lot more to it than just that. 1/2"x28 just isn't best baseline, hindsight is always 20/20.
I just dont understand eliminating a ton of suppressors for the sake of something that's never been shown to be an issue except in theory or extremis (torquing muzzle devices to 100#, etc)
I can’t think of many suppressors I would want today that wouldn’t work with these barrels. Maybe some older ones, so I can certainly see your point if you already own a non-compatible can. However, Sionics RGP is still an option for those.
Btw, @Clint, I decided to hold off on this barrel because I saw that y’all have gas tubes now, and I’m considering using one on a 10.3 instead of the 11.5 plus insert we discussed. More to follow when I make up my mind.
There's a lot more to it than just that. 1/2"x28 just isn't best baseline, hindsight is always 20/20.
What problems have actually been encountered? Not just in theory or in the drawing room, but actual observable issues in absence of material and manufacturing error?
Openly known are the harmonic radius issues that can come up, among others. We would probably rethink some things now, like 5/8" diameter gas blocks with less mass and different retention for the lighter barrel profiles.
Think of what type of defection curve you would get from a whip if you reduced the diameter at the end and added more mass on top of that.
1/2-28 isn't really that bad on its own with an A1/A2 flash hider, its what we can add to that for the above example. We can balance out extension and compression better with the larger diameter thread and look into another way to get a better end goal for possible options.
How are the 11.5” KAC mod 2 barrels? I’ve read mixed claims that their gas ports are smaller, or that they’re standard spec. I’d assume with their newer gas system that they could get away with a smaller port.
Furbyballer
07-30-18, 10:20
How are the 11.5” KAC mod 2 barrels? I’ve read mixed claims that their gas ports are smaller, or that they’re standard spec. I’d assume with their newer gas system that they could get away with a smaller port.
Mine runs like a champ, but is very gassy when suppressed with a KAC QDC can. I can't imagine that it has a smaller gas port.
Unless KAC is doing something differently now, all of my KAC 11.5" barrels from earlier on through MOD 2's have been ported on the leaner side than other offerings. I prefer their porting over most others, they have been my go to recommendations for a lot.
Thanks for the info. My 11.5” BCM with Saker has a lot of gas blowback. So I’m going to shoot more and see if it’s a real issue, but I’m a left handed shooter and end up blinded by the blowback sometimes. I can fight through it but it’s far from ideal.
The Sionics RGP looks the most promising.
It's about minimizing variables and choosing the best design possible to eliminate possible issues.
Sure 1/2 threads work. But are they the best option?
Heavy barrels shoot better because they are thicker and stronger.
Larger 5/8 threads are just an extension of that design intent.
This is especially useful when attaching a suppressor, as the muzzle thread will often be near the center of mass for the combined barrel/suppressor system.
The whole point is to make a better performing barrel.
Sometimes that requires breaking compatibility with conventional options.
In this case, we're just switching to the next larger standard, which is actually very well supported by the market.
If compatibility with a legacy 5.56 suppressor is a requirement, there are other options.
If maximum performance is the goal, these barrels can help take it up a notch.
I just dont understand eliminating a ton of suppressors for the sake of something that's never been shown to be an issue except in theory or extremis (torquing muzzle devices to 100#, etc)
What problems have actually been encountered? Not just in theory or in the drawing room, but actual observable issues in absence of material and manufacturing error?
It's about minimizing variables and choosing the best design possible to eliminate possible issues.
Sure 1/2 threads work. But are they the best option?
Heavy barrels shoot better because they are thicker and stronger.
Larger 5/8 threads are just an extension of that design intent.
This is especially useful when attaching a suppressor, as the muzzle thread will often be near the center of mass for the combined barrel/suppressor system.
The whole point is to make a better performing barrel.
Sometimes that requires breaking compatibility with conventional options.
In this case, we're just switching to the next larger standard, which is actually very well supported by the market.
If compatibility with a legacy 5.56 suppressor is a requirement, there are other options.
If maximum performance is the goal, these barrels can help take it up a notch.
This sounds excellent in theory, but has it ever been expressed with numbers, and quantified? I am unaware of any systemic failures even with the NT4's under heavy heavy (break contact) use. That said, I am sure there is a lot I am unaware of, but would like to know, if it has been a problem.
There have been issues. Might be better to send me a PM WS6.
Sooo...when will we get the 10.3?
.....ported for dedicated suppressor use.
No problem.
https://dqzrr9k4bjpzk.cloudfront.net/images/812059/871651417.jpg (https://www.blackrivertactical.com/concrete5/store/#!/BRT-10-5-OPTIMUM-SGD-Barrel-Suppressor-Gas-Drive/p/112313428/category=1852006)
What is considered full pressure ammo?
What is considered full pressure ammo?
5.56 such as M193/M855
No problem.
https://dqzrr9k4bjpzk.cloudfront.net/images/812059/871651417.jpg (https://www.blackrivertactical.com/concrete5/store/#!/BRT-10-5-OPTIMUM-SGD-Barrel-Suppressor-Gas-Drive/p/112313428/category=1852006)
(Partially deleted after re-read of earlier posts) I think this is the barrel I’ve been looking for.
Why do you feel the need to cut a negative relief between the shoulder and rear of the barrel threads?
Two main reasons.
While most muzzle devices feature a relief cut,
must suppressor mount devices require shims for timing.
Shims such as the Precision Armament have a square shoulder and will interfere with any radius greater than the major thread diameter.
This prevents the shims from seating flush against the shoulder.
Secondly, fundamentals of engineering point toward reducing this diameter under the minor thread diameter for more uniform stress flow and a defined elastic region for the threaded connection.
Why do you feel the need to cut a negative relief between the shoulder and rear of the barrel threads?
Yeah and what about the shims that fall into this relief cut? Like Surefire shims?
I got tired of playing the 11.5” barrel / gas port / 10.X” rail game and put myself on a waiting list for an 11.5” SR-15 with matching KAC silencer this week. Just ****ing tired of it.
snackgunner
08-09-18, 13:04
I got tired of playing the 11.5” barrel / gas port / 10.X” rail game and put myself on a waiting list for an 11.5” SR-15 with matching KAC silencer this week. Just ****ing tired of it.
You seem really upset by this. You only edited your posts 15 times.
Should have bought yourself a colt hrt barrel.
snackgunner
08-09-18, 13:04
I got tired of playing the 11.5” barrel / gas port / 10.X” rail game and put myself on a waiting list for an 11.5” SR-15 with matching KAC silencer this week. Just ****ing tired of it.
You seem really upset by this. You only edited your posts 15 times.
Should have bought yourself a colt hrt barrel.
You seem really upset by this. You only edited your posts 15 times.
Should have bought yourself a colt hrt barrel.
Because I am. And so are a bunch of other people. I wrote a whole essay on this about 6 months ago on here.
I did almost buy an 11.5” HRT barrel. By the time I would have had the front sight base milled down to fit under the abundance of quality 10.X” rails that don’t exist on the market, it was easier to order an SR-15 instead.
Of course Colt can’t release their M5 11.5” upper with Geissele Mk1 10” rail to the public.
snackgunner
08-09-18, 14:58
I asked Shark arms to remove the FSB from my hrt barrel and they did it for me.
SLR Rifleworks 10.7" rails are top notch.
Link to your essay?
Dumb question here, but how would use of an enhanced carrier like the LMT effect optimal gas port sizing?
Because I am. And so are a bunch of other people. I wrote a whole essay on this about 6 months ago on here.
I did almost buy an 11.5” HRT barrel. By the time I would have had the front sight base milled down to fit under the abundance of quality 10.X” rails that don’t exist on the market, it was easier to order an SR-15 instead.
Of course Colt can’t release their M5 11.5” upper with Geissele Mk1 10” rail to the public.
I have been pleased well from the KAC SR-15 11.5" variants over most other offerings. They can be a simpler solution, than messing with changes on others.
Dumb question here, but how would use of an enhanced carrier like the LMT effect optimal gas port sizing?
We've messed with these combinations with no real significant findings. In the time that it takes to quickly swap BCGs, you lose the quick comparability. I really don't find the Ecarriers to do much, and don't run any in any of my guns. Pappabear runs 2 or 3, and they're fine. Getting the gas right is important, and the BCG is a less significant parameter in my opinion.
I got tired of playing the 11.5” barrel / gas port / 10.X” rail game and put myself on a waiting list for an 11.5” SR-15 with matching KAC silencer this week. Just ****ing tired of it.
Are these DI guns?
snackgunner
08-09-18, 18:40
Mark you or papabear run any of the bootleg adjustable bcgs?
Got a link?
Because I am. And so are a bunch of other people. I wrote a whole essay on this about 6 months ago on here.
nightchief
08-09-18, 21:13
Got a link?
https://www.m4carbine.net/showthread.php?202833-Who-s-Genuinely-in-for-a-Geissele-Mk14-10-75-rail/page3
Post #26
I asked Shark arms to remove the FSB from my hrt barrel and they did it for me.
SLR Rifleworks 10.7" rails are top notch.
Link to your essay?
You and I have different philosophies on how do build guns. I’ll leave it at that.
Very generally, the enhanced carrier requires a smaller gas port.
But the effects are a bit variable depending on the particular gas system configuration.
An Optimal configuration such as the 11.5 carbine will see little to no benefit from anything other than a quality mill spec carrier.
how would use of an enhanced carrier like the LMT effect optimal gas port sizing?
For normal use, adjustable gas widgets are unnecessary if the barrel is ported correctly in the first place.
Mark you or papabear run any of the bootleg adjustable bcgs?
Our philosophy is that a quality BCG and quality gas block in combination with an OPTIMUM barrel configuration will yield the best overall performance.
snackgunner
08-10-18, 19:40
You and I have different philosophies on how do build guns. I’ll leave it at that.
Why dont you explain??
KAC 11.5" Mod 2 GP is 0.070"
Don't use paper thin shims.
The PA shims are .060"+ thick.
Yeah and what about the shims that fall into this relief cut? Like Surefire shims?
snackgunner
08-11-18, 18:00
You and I have different philosophies on how do build guns. I’ll leave it at that.
Care on sharing your philosophy?
I just see a bunch of whining from you in here and in your "essay" that was linked.
Just to add emphasis to what Clint is saying. One rotation is just shy of .036", 1/8 of a turn is just shy of .0045". Getting to your desired tension span with required alignment maybe in very small increments of shim thickness. You would never want to use an individual shim that adds 2/3 or less of rotation to a base shim. You want to use a individual shim ideally, or a combination of shims that are thicker than 2/3 of a rotation. When the shims get too thin, they can fall into places that can cause all kinds of trouble.
As for the prior post on the KAC MOD2 11.5" gas port size. I hope that is a measured deviant rather than a newer spec. Deviations happen during manufacturing, KAC does like to drill holes. Not my ideal way, but I understand why they chose their process and I'm fine with it. It's also possible that they changed some other things that would require that port change, it's not a huge difference no matter what. I can't drop a .070" gauge in any of mine, with one exception for their legacies, Christmas Cheers, MOD1, or MOD2 barrels. One MOD1 could drop that gauge, but that particular one shot accurate enough that I would rather mask it with a step up in buffer mass than send it back. That example was only one of very many without that issue.
Clint, I am planning on getting one of your BRT-11-5-OPTIMUM-CQB-Barrels (http://www.blackrivertactical.com/concrete5/store/#!/BRT-11-5-OPTIMUM-CQB-Barrel/p/110110072/category=1852006) that has the barrels gas port sized for **both suppressed and unsuppressed use.** I will also be using the new Surefire optimized long stroke bolt carrier group in this build when they become available along with the new BCM enhanced upper when they are released. For now the suppressor I will be using will be the Silencerco Omega 300, with the Plan B adaptor and Cherry Bomb muzzle brake by Q. My question to you is, when using a bolt carrier group that has a non standard cam pin slot/track like the Surefire or LMT enhanced carrier that increases the dwell time of the bolt unlocking, do these type carriers have any bearing on the barrel's ideal gas port size for my application and (buffer weight and spring assembly), which would be both suppressed 90% and unsupprerssed 10% of the time. Also, could I preorder this barrel now ? Are we looking at September or October availability on these barrels ? Thanks
I'm not Clint, but I can help you with some of your questions.
Delaying the cam timing does reduce the gas port size required to cycle the action to a satisfactory full stroke with a margin the same being for either being equal for the action mass and spring selected.
The production Surefire offering for the standard bolt isn't really in the wild yet, but I do not expect major changes. The Surefire offering for this has a cam timing delay in between the standard and the LMT enhanced. The LMT enhanced BCG stroke length is the same as a normal BCG. With the LMT enhanced offering, the extended cam path increase the AOL of the extended BCG. Having a longer AOL with the standard stroke distance reduces the distance in the bolt face over stroking the magazine. Reducing that distance can decrease the amount of time for the magazine to function, that can hurt reliability when we aren't careful about using an action system that aids in the time delay of that event. The Surefire standard bolt offering has the extended delay that is between the standard and LMT offering, the Surefire uses a longer BCG stroke length that gives more distance in travel in magazine over travel over the standard BCG, that helps with magazine reliability issues as it it gives the magazine more time to properly present the round for chambering. The Surefire system requires a shorter lower mass buffer, the buffer mass is complimented by an internal buffer in the carrier to bring the total reciprocating mass up. The longer stroke for relatively equal masses can increase the gas required for a full stroke slightly.
For the application above, dedicating buffer mass to either suppressed or not individually would be best. That can be highly variable due to the selected ammunition and condition requirements.
There are many pros and cons going with any of the options available. We want to keep the bolt locked for as much time as we can, we want more time in bolt over travel to the magazine, ideally no less than a 20" RLG rifle action. With all of our available options, you would want to address major concerns over more minor ones for the combination chosen.
Sooo...when will we get the 10.3?
.....ported for dedicated suppressor use.
yes please, but in 1/2x28 for use with a brevis direct thread
.
That sounds like a real nice combo, especially with the Cherry Bombed Omega.
Special carriers have somewhat limited utility in Optimum configuration barrels.
We're shooting for October availability on all 5 of these new OPTIMUM series barrels.
We've got a couple things to line up and then we'll open up pre-order for them.
Clint, I am planning on getting one of your BRT-11-5-OPTIMUM-CQB-Barrels (http://www.blackrivertactical.com/concrete5/store/#!/BRT-11-5-OPTIMUM-CQB-Barrel/p/110110072/category=1852006) that has the barrels gas port sized for **both suppressed and unsuppressed use.** I will also be using the new Surefire optimized long stroke bolt carrier group in this build when they become available along with the new BCM enhanced upper when they are released. For now the suppressor I will be using will be the Silencerco Omega 300, with the Plan B adaptor and Cherry Bomb muzzle brake by Q.
My question to you is, when using a bolt carrier group that has a non standard cam pin slot/track like the Surefire or LMT enhanced carrier that increases the dwell time of the bolt unlocking, do these type carriers have any bearing on the barrel's ideal gas port size for my application and (buffer weight and spring assembly), which would be both suppressed 90% and unsupprerssed 10% of the time.
Also, could I preorder this barrel now ? Are we looking at September or October availability on these barrels ? Thanks
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.