Are you using an Adj gas block?

[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]

Drillboss... We are talking about adjustable gas blocks vis-à-vis suppressors. I am saying they are not essential, but they help. As I understand 52 he is advocating not using them regardless because of increased port erosion. I am saying that is pretty damning advice given their prevalence in the market. So it's the old case of requesting justification...and I am still unconvinced.

I have used both regulated and unregulated blocks with suppressors and have done for a while now. They both work, however regulated gas makes an automatic system more user-friendly. The caveat is the Blackout which is under-gassed as a calibre to start with, so if you want to shoot subsonic 300BLK reliably then you need the port fully open. A fully-open regulated gas block in that case is just a waste.

I was originally issued with the SLR L1A1 (licensed equivalent of the FAL L1A1) in our military. I have never heard of carbon welding in the L1A1. They get carbon stains on the gas parts just like other gas guns but never did any parts 'weld' together.

I think port erosion is a non-issue in the choice between adjustable and non-adjustable gas for an AR. My concern about adjustable is similar to Keystone's however in that when you add moving parts to a system it increases the risk of failure. So far the only issue I have had was the choke screw on a new block out of the box would not move/stuck so Todd at SLR replaced it immediately.

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.

[jonny rotton]

what is the procedure you use to adjust an adjustable gas block?? i am putting one on my new 12". it was the only one i had sitting around

[explorecaves]

Start with it closed and fire one round at a time till it locks back on the empty mag. Then open one more click. Should be good to go on most ammo at that point.

[A5BLASTER]

Start it wide open and load one round in mag fire and lower gas each round till it doesn't lock back then turn back half turn and fire round if it locks back lock it down and shoot ten rounds if no problems happen your set, if it has a problem unlock the block and open anouther half turn and re lock the block it should be set.

That's how I did it, but have done it the way Explorecaves posted and I didn't care for it because it was a pain to extract the empty case because the bcg didn't get any gas and it didn't allow the bolt to completely unlock, but both ways do work fine.

[explorecaves]

I usually do some research to find where people have theirs set (number of clicks or turns) and then close it 1-1.5 turns and work my way open till it locks back

[jonny rotton]

thank you all for your advice!! i appreciate it.

[Klem]

thank you all for your advice!! i appreciate it.

SLR Rifle works advices customers to start in the middle and work up or down. I will add that the best spot is where it locks back on last round. Either stop there or go one further to be sure. So load mags of one round at a time.

I agree with Speleocaves. Fully closed tends to stick the bolt in place and makes it difficult to open with no compound leverage of a charge handle.

[The Profit Joseph Sith]

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....

You shoot their wings off? Thats easy, try and keep em buggers from breeding..

[Kswhitetails]

You shoot their wings off? Thats easy, try and keep em buggers from breeding..

Those Dragon's Breath 12ga shells work great on gnat clouds.

We don't have clouds around here anything like down in LA though. We were traveling to Shreveport for a conference once and the swarms on the side of the highway looked like they could carry off our car if we swerved into one...

[Hansel&Grendel]

FWIW, I've used SLR Rifleworks Sentry 7 adj. gas blocks (clamp-on) on my Criterion 6.5G 16" and 11.5" SBR (the latter with a Law Tactical folding stock adapter). I've also used them on other builds for myself and others. Mark at PF worked his magic on the Criterions including nitriding them. With the SBR, I use a JP LMOS BC with Mark's 6.5G bolt, a carbine buffer (3oz) and a JP Custom Centerless ground/polished carbine buffer spring. The rationale was to use a lower weight BC because the Law Tactical BC insert itself weighs 2.2 ounces. I have the SLR on click 5 from closed.

An SLR gas block adjustment screw on a .223 Wylde build did freeze. I loosened it but SLR replaced it gratis with a newer design (great CS). So, when servicing the barrel, I click the SLR to fully closed to keep solvent out of the gas block and to also loosen any carbon deposits on the gas block adjustment screw.

The SBR shoots very nicely with quick follow-up shots, i.e., recoil is a bit more than my 16" AR 7.62x39. However, the 6.5G SBR annihilates at CQB and is lethal to at least 600 yards I'm sure. Not bad for a truck gun. Hopefully, port erosion won't be an issue although the nitriding does calm the mind. Lastly, 2A Armament makes a regulated BC as a means, in part, to alleviate port erosion; however, it is incompatible with the Law folder.

Hans