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Maybe a stupid question. Can you use a 14-16 AGB on a 10.4 barrel?

Any issues? Modifications needed?
 

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Maybe a stupid question. Can you use a 14-16 AGB on a 10.4 barrel?

Any issues? Modifications needed?
You have increase the bore of the barrel gas port/vent. I think its out to 1.9mm but I’ve yet to have it done. That is the diameter I believe a regular 14.5/16” gas block needs on a 10.4” barrel. I assume that’s what you would use for the AGB as well. YMMV.
 

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The AGB (adjustable) has selector port sizes of 1.6mm or 1.4mm, thus the barrel port needs to be opened to at least 1.6mm to work as intended. If it isn’t, then the barrel gas port will be more restrictive than the selector. If opened larger, the selector will be the restriction. What does a 1.9mm port do for you if it’s immediately restricted to 1.6mm or 1.4mm?
 

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The 1.6mm and 1.4mm specifications you list are for the 10.4 AGB. It also has a significantly smaller gas vent than a 14.5 GB.

1.6mm unsuppressed, 1.4mm (restricted flow) for suppressed.

A 14.5 GB has a significantly larger vent due to the increased dwell time.

Using a 10.4 AGB on a 14.5/16 barrel will result in massive overpressure regardless of the setting.

It would logically track that an AGB for a 14.5 would have similarly sized vents and gas ports based on the non-AGB specifications to account for dwell time.

That being said, using a 14.5 AGB on a 10.4 would require similar port modification to account for the excess gas bleed off from the larger vent.
 

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I’m referring to the Norwegian AGB intended for longer barrels (not 10.4), they have 1.6/1.4mm selector and 1mm vent. They can be used on a 10.4” barrel provided the barrel gas port is opened to at least 1.6mm like I mentioned. In fact, the vented gas block for the 10.4” barrel uses a 1.6mm gas port and a 1mm vent.

I measured the port sizes I mentioned with pin gauges. Can you post the selector and vent sizes for the 2 AGBs you’re referring to? Thanks.

Edited to add: what factory HK barrel has a 1.9mm gas port?
 

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Sigh. You are mistaken that the AGB's you talk of are for 14.5 guns. They are not.

The vented non-AGB for the 10.4 has a 1.6mm barrel gas port with a 1mm overall vent. Meaning that it retains positive pressure due to the short dwell time, yet does allow bleed off compared to the original non vented 10.4 GBs.

The available 10.4" AGB's have the 1.6mm/1.4mm vent settings with a 1mm overall exit vent, and require a 1.6mm gas port in the barrel. Meaning that regardless of the setting, the system retains positive pressure due to the short dwell time of the 10.4 barrel, yet slightly restricts gas flow on the 1.4mm setting to account for suppressor use.

Now stay with me here....

The non AGB 14.5/16 GB's have a 1.4mm overall vent and require a 1.4mm gas port on the barrel. Meaning that the system reaches a neutral pressure once the vent opens due to the extended dwell time compared to the 10.4 GBs.

To use a non-modified vented 14.5 GB on a 10.4 gun, the barrel gas port MUST be opened up to 1.9mm when using a factory buffer/spring combo otherwise the gun will be under gassed.

Thereby it logically tracks that if an AGB made for a 14.5/16 gun with appropriate dimensions to use the 1.4mm gas port and account for the extended dwell time and has a similarly larger (1.4mm) overall vent, would still require the 1.9mm gas port on the barrel if used on a 10.4" gun.

An AGB for a 14.5 gun would have the large setting of 1.4mm (to match the barrel port) and a smaller setting (most likely around 1.2mm) for running suppressed. Not a 1.6mm "normal" setting and the exact same adjustment port size as gas port size, and retain the 1mm overall vent at the same time.

The mere fact that the AGB's we've seen thusfar have a 1mm overall vent is alone enough information to know that they are not appropriate for a 14.5/16 inch gun.

Especially considering that the Norgs simply changed gas blocks on the 14.5 guns, not barrels, simply for the sake of having a more durable AGB, not for function issues.

To assume that the AGB's you find are suitable for the 14.5/16 barrels is a little silly given the dimensions and dwell time involved. Especially considering that nowhere has HK mentioned opening the gas port on a 14.5/16 barrel to 1.6mm. This has ONLY been the case for tuning a 10.4 barrel to run with a newer vented GB.

We can break it down to a "pressure retention" system.

14.5/16 + standard vented GB = 1.4mm gas port - 1.4mm gas vent = neutral pressure when vent opens.

10.4(original) + standard non-vented GB = 1.4mm gas port - 0mm gas vent = +1.4mm of positive pressure retained(the originally severely overgassed system that lead to excessive bolt speeds and broken discos).

10.4(new) + vented GB = 1.6mm gas port - 1mm gas vent = .6mm positive pressure when vent opens.

10.4 + AGB on unsuppressed setting = 1.6mm gas port - 1mm gas vent = .6mm positive pressure when vent opens.

10.4 + AGB on suppressed setting = 1.4mm restricted gas port - 1mm gas vent = .4mm positive pressure when vent opens.

10.4 (original) + 14.5 standard vented GB = 1.4mm gas port - 1.4mm gas vent = zero positive pressure with minimal dwell time and excess bleed off after vent opens.

10.4(new) + 14.5 standard vented GB = 1.6mm gas port 1.4mm vent = .2mm positive pressure with minimal dwell time and excess bleed off after vent opens.

10.4 (modified) + 14.5 standard vented GB = 1.9mm gas port - 1.4 vent = .5mm positive pressure on vent open. (the minimum required to run well and reliably lock back on last round of the magazine)

The 10.4(modified) with 14.5 vented GB and a 1.9mm gas port run quite well both suppressed and unsuppressed without being over gassed. For those who do not wish to run suppressed, I would suggest a 2mm barrel gas port to get the .6mm retained positive pressure in the system.

Were there to be a dedicated AGB for a 14.5/16 barrel, it would have to have a restricted setting >1.4mm and retain the 1.4mm vent thereby having a negative pressure on vent open to account for the extended pressure spike caused by the use of a suppressor, OR if HK did call for the gas port to be opened to 1.6mm on a 14.5/16 barrel, the overall exit vent on the GB would have to be 1.6mm as well.

Were you to place a 10.4 AGB on a 14.5 barrel, you would lose the neutral pressure vent open system and have 4.1 inches of dwell time at .4mm positive pressure regardless of the setting you placed the selector at. Meaning it would be a wash regarding exit vent and the system would now retain positive pressure beyond what it was designed to handle.

And if you were to open the barrel gas port to 1.6mm, now the system has an extra .6mm positive pressure on the unsuppressed setting thereby overgassing the hell out of it even more.

Logically, your line of thinking simply does not track with the proven operating parameters of the 416 gas system.
 

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^^^^^Just like Goodwill Hunting, “he’s wicked smaat”. ^^^^^

(My attempt at a south Boston accent)
 

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That’s all great in theory, and you have a lot of them, but there’s no facts there. Maybe you could start by posting the valve sizes for the long barrel AGBs? Or even which HK barrel has a 1.9mm port? Or for that matter, any facts at all??

I know, you’re always right regardless. You suggested a 1.9mm gas port for a long barrel AGB without even knowing the port sizes, WTF?!?

Carry on, it’s all yours.
 

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That’s all great in theory, and you have a lot of them, but there’s no facts there. Maybe you could start by posting the valve sizes for the long barrel AGBs? Or even which HK barrel has a 1.9mm port? Or for that matter, any facts at all??

I know, you’re always right regardless. You suggested a 1.9mm gas port for a long barrel AGB without even knowing the port sizes, WTF?!?

Carry on, it’s all yours.
No OEM barrels have a port size of 1.9mm. IT says that is what works with a 14.5”/16” gas block on a 10.4” barrel.

He knows because he does it for a living.

The barrels he's done for me work smooth as butter, with and without suppressor.

I suggest you go do your own homework, get your hands dirty and post a credible rebuttal if you are so sure that IT is so off the tracks here... .

PS - I have a buddy who has been flying through bolts on his shorty because he’s shooting suppressed with a non-vented block and cracking the bolt heads.
 

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Sure, some facts:

IT has no experience with the long barrel AGB. IT shortened a MR and when it wouldn’t run, enlarged the barrel gas port to 1.9mm to get it to run. Not surprising from someone familiar with ARs and not familiar with HKs. Hk does NOT do this, they use the same size barrel gas port and adjust the gas block vent accordingly. If IT was “smaat”, he would have welded the gas block port and drilled it to 1mm. This is what Hk did going from no gas block vent to 1mm on the 10” guns.

I, on the other hand, do have personal experience with the long barrel AGB. I purchased one, just like anyone can from vendors like Hkspecialist or Hurricane Butterfly. I posted the valve and vent sizes above. From both vendors I mentioned, they’re specifically advertised as long barrel AGBs, they’re NOT for the 10” guns. They’re $299 and in stock at both locations.

So, IT, who has no experience with the AGB claims that I somehow got a 10” version instead. IT further speculates what valve and port sizes must be on the long barrel AGB by assuming it’s the same as the non-adjustable long barrel gas block. Worse, IT makes barrel gas port size suggestions to others based on this speculation. This is isn’t “smaat”, it’s dumb. I realize IT has a huge superiority complex, chooses the baffle ‘em with bull**** approach, likes to talk down to others, and thinks that his non adjustable gas block is somehow optimized for both suppressed and unsuppressed, which isn’t possible, but making suggestions to others based on his assumptions is not only dumb, it is also irresponsible!

Is it possible that I somehow got a 10” AGB instead, I suppose, but it certainly doesn’t make any of this any better! In the meantime, I’ll wait for IT to post the valve and vent sizes for the long barrel AGB.

Why don’t you buy a long barrel AGB like I did and clear all this up for everyone? Hopefully, they won’t send you the 10” by mistake!
 

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Sure, some facts:

IT has no experience with the long barrel AGB. IT shortened a MR and when it wouldn’t run, enlarged the barrel gas port to 1.9mm to get it to run. Not surprising from someone familiar with ARs and not familiar with HKs. Hk does NOT do this, they use the same size barrel gas port and adjust the gas block vent accordingly. If IT was “smaat”, he would have welded the gas block port and drilled it to 1mm. This is what Hk did going from no gas block vent to 1mm on the 10” guns.

I, on the other hand, do have personal experience with the long barrel AGB. I purchased one, just like anyone can from vendors like Hkspecialist or Hurricane Butterfly. I posted the valve and vent sizes above. From both vendors I mentioned, they’re specifically advertised as long barrel AGBs, they’re NOT for the 10” guns. They’re $299 and in stock at both locations.

So, IT, who has no experience with the AGB claims that I somehow got a 10” version instead. IT further speculates what valve and port sizes must be on the long barrel AGB by assuming it’s the same as the non-adjustable long barrel gas block. Worse, IT makes barrel gas port size suggestions to others based on this speculation. This is isn’t “smaat”, it’s dumb. I realize IT has a huge superiority complex, chooses the baffle ‘em with bull**** approach, likes to talk down to others, and thinks that his non adjustable gas block is somehow optimized for both suppressed and unsuppressed, which isn’t possible, but making suggestions to others based on his assumptions is not only dumb, it is also irresponsible!

Is it possible that I somehow got a 10” AGB instead, I suppose, but it certainly doesn’t make any of this any better! In the meantime, I’ll wait for IT to post the valve and vent sizes for the long barrel AGB.

Why don’t you buy a long barrel AGB like I did and clear all this up for everyone? Hopefully, they won’t send you the 10” by mistake!
Rereading your post, I actually understand what you are saying.

Would mind posting your measurements again:

Barrel gas port size
AGB intake gas port size
AGB regular gas port sizes

Thanks and glad I reread it.
 

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Further adding to the confusion, the only photos I've been able to find of AGBs with sling loops is on 10.4 inch barrels.
 

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I measured my AGB with pin gauges at 1.6 and 1.4 mm for the valve and 1mm for the vent. I never posted the barrel gas port size, but it’s 1.5mm.
 

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Well, now i'm irresponsible and a dumbass. How cute.

You've clearly convinced yourself of your superiority by measuring out a 10.4 AGB and throwing around the measurements as if it makes you an expert, hilariously so considering your measurements are for a 10.4 AGB.

Welcome to last year, kiddo.

Clearly, reading comprehension, critical thinking, and deductive reasoning are not exactly your best characteristics.

Nobody ever said to open a 14.5/16 to 1.9mm. RIF.

I'd like for you to produce your "facts" that opening a gas port to 1.9mm on a 10.4 barrel for the use of a 14.5 GB is "irresponsible" and doesn't run both suppressed and unsuppressed. With all of your extensive knowlege, this should be easy.

You also did not factually nor logically refute my positive/neutral/negative pressure breakdown of the various gas blocks to barrel setups.

Please explain how HK decided that adding .4mm of positive presure to a 16" barrel that already worked fine, is a good idea. Add to this exactly what the gas port should be on said rifle running an AGB with a 1mm vent and the 1.6mm/1.4mm port restrictions. Since you have all the details, dish the dirt.

Explain why the AGB measurements you have would coincidentally work perfectly with an upgraded 10.4 barrel (1.6mm port), yet you seem to think it's meant to run on a 14.5/16 system.

I challenge you to place said AGB on a 14.5/16 barrel and report back your findings on the difference in function/brass throw/bolt speed on the different settings.

Bonus points if you film yourself shooting it suppressed on both settings as well!

Given that the point of the AGBs are to run with/without a suppressor, i'd like to know your "expert"opinion on gas port vs. restriction settings vs. vent size interaction and what you think they EXACTLY are for a 14.5/16 barrel? Especially considering that you think your magic AGB is for a long barreled gun.

Based on your angry, lack of actual facts and data rantings, i'm going to call your "experience" the tip of the dunning-kruger iceberg.
 

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Can anyone actually say for certain there are different versions of the non-A5 AGBs for different barrel lengths?
 

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Can anyone actually say for certain there are different versions of the non-A5 AGBs for different barrel lengths?
Yes, there are 2 different versions. The one for the 10.4” barrel has a 1mm vent, and the adjustable regulator has a 1.6mm port for unsuppressed shooting and a 1.4mm port for suppressed shooting. The 14.5”/16” barrel version has a 1.5mm vent, and the adjustable regulator has a 1.4mm port for unsuppressed shooting, and a 1.2mm port for suppressed shooting.
 

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Aren't the 10” AGBs marked with the single indent on the side and the longer barrel versions smooth? I know zib offers both.
 
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