Are you using an Adj gas block?

[LRRPF52]

With respect, until there is some hard evidence that either accuracy or barrel life suffers to a greater extent when using adjustable gas blocks then I don't think you can make such a claim. Certainly not with such matter-of-fact authority. Linking port erosion to adjustable gas blocks and then advising that non-adjustable is better than adjustable blocks is a non-sequitur.

I am with Keystone on this one. I have used SLR adjustable blocks in 5.56 and 6.5 uppers. They have all performed flawlessly. I agree however that the newer clamping-style blocks are an inherently better design than the older set screws.

Adjustable gas blocks are not essential for a suppressed AR, but they do help tame the increase in port pressure. This is evidenced by the brass ejection pattern.

I never thought about it until Bill A. mentioned it, based on decades of engineer-level analysis and a 1-2 hour conversation on some of what he's seen with various adjustable gas designs, from the FAL to regulators on machine guns.

Seemed odd to me at first, but then again, every time I doubted him on something, I was wrong in the end, learned the hard way on my own.

He used a lot of his experiences when designing the Ulfberht gas system, as carbon welding is an inevitable that has to be deal with eventually. He said the FAL (L1A1) gas would carbon weld as well, and they had to repair them at that level in MoD.

Adjustable gas systems control how much gas flow there is through the port. When you constrain the flow, it leads to increased erosion. Smaller ports experience less erosion because there is less surface area for the expanding gases to impact and change direction through. It's why LMT uses angled gas ports on the MRP and MWS barrels, like the old AK gas port (only AK gas ports are monstrous in size).

[montana]

I'm going to have to agree with Klem on this subject. All of my Grendels and most of my 5.56 rifles have adjustable gas blocks. My 18" AA barrel needed the adjustable gas block since it came way over gassed and would not function with out it. The only effect with the increase port erosion, "if there is any" would be in accuracy and I doubt there would be enough compared to the life of the barrel in the first place to be concerned with . I too would like to see some hard evidence since my experience has shown differently. I have not had any problems with carbon welding since I clean and move my adjustment screw periodically. The new AK's have switched to the 90 degree port since they had problems with bullet jacket shearing with the 45 degree port. In any case having the ability to adjust my gas for my loads has out weighed any theory based problem with port erosion.

[Klem]

I love all of y'all, but are you possibly talking past each other? I don't have first hand experience with suppressors, but from what I've read, adjustable gas is the way to go with them. I've put together 4 Grendel uppers without adjustable gas (and without suppressors) and they've all ran fine. A properly sized gas port seems to do the trick without suppression.

[2_speed]

What do Y'all think about "bleed-off" gas blocks such as the Superlative Arms?

https://www.rainierarms.com/superlative-arms-adjustable-gas-block-bleed-off

I bought one but haven't tried it out yet. (Sounds like a heck of a theory.)

Tom

[Klem]

What do Y'all think about "bleed-off" gas blocks such as the Superlative Arms?

https://www.rainierarms.com/superlative-arms-adjustable-gas-block-bleed-off

I bought one but haven't tried it out yet. (Sounds like a heck of a theory.)

Tom

Looks like it is a similar principle to the gas system on the FAL L1A1 (mentioned above).


If that vented gas is not performing work; either pushing the bullet, or the BCG then it is being wasted to the atmosphere. If this vented gas does not drop the muzzle velocity significantly then I guess it's no big deal. But, it needs to be of some tangible benefit over existing designs to justify venting gas.

[Sticks]

I watched a promo video for that (Supurlative Arms) AGB. Video showed the gas/smoke coming out with a standard GB and towards the shooter, then the next series with the same rifle (trying to keep all things equal) the shooter commented on no smoke...the wind had changed directions and was coming from behind the shooter, blowing it all down range.

Not sure how to take the effectiveness of a bleed off system.

[keystone183]

I never thought about it until Bill A. mentioned it, based on decades of engineer-level analysis and a 1-2 hour conversation on some of what he's seen with various adjustable gas designs, from the FAL to regulators on machine guns.

Seemed odd to me at first, but then again, every time I doubted him on something, I was wrong in the end, learned the hard way on my own.

He used a lot of his experiences when designing the Ulfberht gas system, as carbon welding is an inevitable that has to be deal with eventually. He said the FAL (L1A1) gas would carbon weld as well, and they had to repair them at that level in MoD.

Adjustable gas systems control how much gas flow there is through the port. When you constrain the flow, it leads to increased erosion. Smaller ports experience less erosion because there is less surface area for the expanding gases to impact and change direction through. It's why LMT uses angled gas ports on the MRP and MWS barrels, like the old AK gas port (only AK gas ports are monstrous in size).

So i guess i need to ask Bill A nicely to explain it to me?

[Bradpierson26]

Adj gas block and rifle gas tube on the way. Waiting on the group buy bolt and of course the 20" group buy barrel due sometime in 2018 haha

[LRRPF52]

Nowhere have I said not to use them, and I think many rifles need them that are suppressed.

I'm saying if the gas system is worked out correctly from the start, there is no need for them.

[Klem]

The main reason not to use adjustable gas if you don't need it is port erosion.

You just took an open port and put a choke over it, turning it into a combustion chamber rather than the outlet for a manifold. There are ways to counteract that with nitriding and other processes, but I personally don't use Adjustable Gas if I don't need it.

OK, I misinterpreted the above statement. I thought you were advising the poster.

I realise there's some back-peddling going on but let's be clear about one thing, port erosion is a non-issue to end-users of the AR15. It's an impressive-sounding topic but as soon as it starts to influence product choices that's when we need to put the brakes on with a reality check. As far as barrel life, accuracy and reliable cycling is concerned port erosion affects none of them. If adjustable blocks erode the port faster than non-adjustable blocks (and I am still unconvinced of this) then this means precisely nothing when compared with normal barrel wear-and-tear. Notwithstanding, the barrel wears more at the throat and early lands, coinciding with the peak pressure spike. Not down at the port when the pressure has dropped.

My advice to the op is get whatever block you like. They all work. With a suppressor an adjustable gas will help govern the gas to a level that is more user-friendly, but it is not critical in most cases. If you suspect your gun is over-gassed even without a suppressor then an adjustable gas will fix that also. Without the need to resort to full-mass BCG's and heavier buffers.

[LRRPF52]

Just having a poorly-cut or ragged gas port in the bore most certainly will affect accuracy, and I've seen it first hand with an SPR barrel that was select match Douglas.

If port erosion changes the geometry of the port, and metal is galling into the lands, it will have unbalanced drag on the jackets as they pass through that portion of the barrel.

Everything I have seen and heard from smiths that look for the utmost accuracy in AR15s indicates that they take time to make sure the port geometry is carefully cut, cleaned, and positioned in the land.

[keystone183]

I'm confused now. Have we decided INCREASED port erosion from an ADJUSTABLE block IS OR ISN'T a real thing?

[explorecaves]

I'm confused now. Have we decided INCREASED port erosion from an ADJUSTABLE block IS OR ISN'T a real thing?

Unless you can shoot the wings off a gnat at 300 yards, you will be replacing the barrel due to chamber erosion long before you will notice an issue due to port erosion irregardless of gas block type. They are just nitpicking the minutia....

[Klem]

I'm confused now. Have we decided INCREASED port erosion from an ADJUSTABLE block IS OR ISN'T a real thing?

To be clear, I doubt the claim that adjustable gas blocks erode faster than non-adjustable. However, given there is no empirical evidence to suggest either way then the correct answer would be to say...we simply do not know (all of us). It is yet to be proven or disproven.

I am also saying that regardless of if it is true I think it is moot. Moot in the decision to buy one type or the other. Both types of block are capable of sealing the area around the port equally. If any erosion is happening it still remains effectively sealed until it is time to replace the barrel for some other reason. All the normal reasons like wear-and-tear on the throat, lands and crown, which for some shooters is going to be years down the track.

As for blocks leaking gas, frankly I think this is moot also. Any venting of gas through imperfect seals is rarely to the extent that reliable cycling or accuracy is affected. As long as reliable cycling happens for the life of the barrel then your block has done its job. I know some of you glue your blocks for a better seal but I don't. I just don't care about minor leaks. I don't believe leaks around a gas block affects accuracy, certainly not to the extent that a block of metal sitting half-way down the barrel and connected to the receiver by a gas tube does. I know marketers have the hide to call AR15's 'Free floating' but that is where the block is going to influence accuracy, by just being there and connected to the receiver, and syphoning gas, not because it might leak. My opinion is different from 52's on this point and I accept that, and respect his.

The idea of the port 'galling' the round as it passes is an interesting one, but moving away from the thread topic of adjustable/non adjustable blocks for suppressors. On this I agree with 52. If the port drilled by the manufacturer to enter the barrel half way on a land and half on the adjacent groove then I can see how this might occur. It certainly makes lapping the drill-hole burrs more difficult (which cheaper barrel manufacturers don't do). If increased port erosion is happening over the life of the barrel however I can imagine it might actually help the gas flow rather than gall the bullet. Port erosion lapping the port?

All that said, I'm quoting Shakespeare on port erosion, 'Much ado about nothing'.

[TCBM]

The main reason not to use adjustable gas if you don't need it is port erosion.

You just took an open port and put a choke over it, turning it into a combustion chamber rather than the outlet for a manifold. There are ways to counteract that with nitriding and other processes, but I personally don't use Adjustable Gas if I don't need it.

I have had to use adjustable gas ports.

In other fields, gas erosion is caused by temperature and mass flow of the gasses. The temp and mass flow rate implies a BTU content that heats small portions of the steel to the melting point, briefly. Restricting the flow rate of the gasses reduces the total heat (BTU) applied to the steel around the gas port. As the flow approaches zero, the gas port conditions approach that of the rest of the barrel. It seems very unlikely that restricting gas flow with an orifice would increase the temp of the walls of the gas port, an orifice itself.

This is less like putting your thumb over a hose end, though both reduce flow, because a gas is compressible and does not increase velocity (almost) proportionally the way water does.