Gas Block question - Yankee Hill Machine suppressor gas block

[zukiphile]

My first rifles and carbines were made with 5 ounce carbine buffers and 7 ounce rifle buffers. I've since tried a Superlative Arms gas block with a lightweight bolt carrier and empty buffer; it was easy to tune and gave bizarrely light recoil. Today I tried an Odin Works adjustable on a 13.7 midlength, and I'm not impressed with the result. Good enough accuracy, but it went from cycling at 4:30 and locking back directly to not ejecting in just one click. When I tune with bolt carriers and buffer weights, I often hit a point at which the rifle cycles but doesn't lock the bolt back.

My question: Has anyone used a Yankee Hill Suppressor gas block without any suppressor, and gotten it to cycle/lock back with just reduced weight bolt carrier and buffer? It has a .054 or .055 gas port. https://yhm.net/new-products/suppressor-gas-block/

 

[FrankenMauser]

That gas port seems a bit small.
The double restriction may be too much, when the gas block is nearly closed.
I have an Aero Precision adjustable on a .936" barrel. Adjustability is just fine. But, I am also working with a 0.106" gas port (big - big by all standards - even chunky rifle-length, .936 standards). The gas block does all of the work on that one, not the gas port.
I tried a YHM, but it seemed to act as too much of a restriction. Made an already barely-cycling action short stroke most of the time - even fully open.

What's the problem with ejecting at 4:30?
The average AR that ejects at 2-3 can be turned into a 5 o'clock ejector with the change of a spring, extractor, or ammo. Don't read too much into the old ejection angle fuddlore.

 

[zukiphile]

4:30 ejection doesn't bother me, but I think it's weird that it went straight from locking the bolt back to not even ejecting in one adjustment. I think it wasn't even unlocking judging by the recoil impulse. The Odin Works GB is a front screw type with 20 clicks of adjustment.

The YHM GB I'm looking at is non-adjustible and I'm a fan of simplicity. Your comment about the double restriction shook a thought loose. I have a BA Hanson barrel with a gas port so small I wasn't able to use a piece of Barilla thin spagetti to find the correct alignment. I'm not sure how I'd align a .055 gas block. Looks like I'll have to source some angel hair.

 

[tangolima]

For adjustable gas block, I prefer non-click type to click type, because of the finite "step size" of the latter.

Each click turns the screw by the same angular amount, say 45 degree. Due to the circular shape of the orifice, percent change in area available to gas flow is not the same for each click. It is finer near fully open or close, and coarse in the middle.

If you 4:30 set point is near the middle, you can move it closer to fully close / open to have finer adjustments. There are a few ways to do it, enlarging the barrel's gas port diameter being one.

Having said that, I would probably leave it alone. If it really bothers you, you may consider getting a cheap non-click gas block. The adjustment is continuous.

-TL

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[zukiphile]

TL, the way you've explained this the concepts are clear, but implementing them would take crossing the limit of my handiness. If I drill a gas block and ruin it, I won't have also ruined a barrel.

I have misgivings about a non-click type moving over time, but I've not spent much time with those. I read the adjustment mechanism in a GB described as a potential failure point, but I'd guess that on the click type by the time the detent ball spring dies from heat cycles the whole mechanism would be fixed by carbon.

Thanks both for your insights.

 

[tangolima]

Non-click block come with 2 screws. The main screw to control the orifice area, and a set screw to lock the main screw. So it is not too bad.

Click or non-click will require re-adjustment as time goes by anyway. Carbon deposit or gas cutting etc. Even going to other load will change things too. I wouldn't lose much sleep over it.

I tend to over gas my guns for better reliability, even with adjustable gas blocks. 2 o'clock doesn't bother me.

-TL

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[FrankenMauser]

I'm not sure how I'd align a .055 gas block. Looks like I'll have to source some angel hair.

For gas block / barrel combinations where alignment is critical, due to very close port diameters, I use a bore scope during installation.

The photo below, for example, was that 0.106" gas port and YHM gas block, which had a port only fractionally larger than the barrel's gas port.
Everything is out of focus, because the scope was set to focus on the hard edges around the gas port in the gas block bore - which are no longer visible after being aligned.

It is possible to still have an alignment issue with the gas tube and gas key in the receiver, after aligning the gas ports as well as possible. But barrels that needed this have had gas key alignment within limits for me, so far.

I normally take a few measurements and use a paint marker to put some alignment marks on the block and barrel for more forgiving combinations (and take a measurement for port distance from the shoulder), and then remove the paint with acetone after installation. But sometimes, it needs to be a little more precise than that.

 

[tangolima]

I thought it was hard to align gas port. It turned not bad. The hole in the gas block is usually significantly larger than the gas port drilled in the barrel. Those 2 circles don't really need to be concentric. It will work the same as long as one circle is not "cutting the cake" of the other.

Dimpled barrel with set screw gas block is pretty hard to miss. Pinned block is slightly trickier. Different methods to align. Bore scope works great. Angel hair is neat.

-TL

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[stagpanther]

Dimpled barrel with set screw gas block is pretty hard to miss.

Assuming the port location on the block lines up properly with the dimple location on the barrel. I recently did an install on an AR where the block in question's set screws location resulted in a mismatch with the barrel's port--no go on the gas system.

 

[tangolima]

Assuming the port location on the block lines up properly with the dimple location on the barrel. I recently did an install on an AR where the block in question's set screws location resulted in a mismatch with the barrel's port--no go on the gas system.

Yeah I heard about that, although I haven't seen one yet. I'd hate that. Worse than pin-on. It would sucks if the dimples are just off slightly.

-TL

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[stagpanther]

For gas block / barrel combinations where alignment is critical,

Now that is a well-done gas port in the bore--brings happiness to my eyes; who did the barrel?

 

[9x19]

I've yet to come across a block where the rear set-screw hole isn't aligned with the port above, but I've only started checking that based on Stag's experience.

Prior, I just figured the rear set-screw hole was the same hole they used to drill the port above it, so....

I've always only dimpled for the rear set-screw because I do find that front screw location can vary based on maker, and I don't want to be tied to just one brand.

 

[zukiphile]

I thought it was hard to align gas port. It turned not bad. The hole in the gas block is usually significantly larger than the gas port drilled in the barrel. Those 2 circles don't really need to be concentric. It will work the same as long as one circle is not "cutting the cake" of the other.

Has anyone tried this intentionally?

I did this accidentally. I tried an Odin Works adjustable with a handguard cap. My guess is that those gas blocks aren't made to stand off a bit from the journal shoulder. At wide open, the rifle would cycle Brown Bear steel cased, but would not lock the bolt back. With full power brass, a lightweight BCG and an empty carbine buffer, it worked nicely.

 

[FrankenMauser]

Now that is a well-done gas port in the bore--brings happiness to my eyes; who did the barrel?

I did.
I shoved a greased, but grit-free BTB 'bore lapping' bullet down the bore to the gas port, drilled incrementally, making sure to dimple the lead slug by about 0.060". Then tapped the slug forward about 0.050" before pushing it out the chamber end (to not screw up the muzzle end, just in case it dragged the chip down the bore, rather than catching it in the 'dimple').

During the process, I found the crown to be tapered. It was not, originally. I believe the idiot (not me) that threaded the barrel ruined it. So, the barrel immediately got pulled and sent off to be cut back and re-threaded. The 'smith did a great job. It has a great crown now.

Assuming the port location on the block lines up properly with the dimple location on the barrel. I recently did an install on an AR where the block in question's set screws location resulted in a mismatch with the barrel's port--no go on the gas system.

I have run into that at least twice.

Another mismatch that I've seen at least twice is with gas block shoulder vs port location in the barrel, combined with gas block port location vs the dimension to the back of the block - where it contacts the shoulder.
I do not recall the brand, but one of them was subsequently discovered to be sold as a "dissipator" gas block (the hidden gas block with no hand guard cap allowance to the shoulder), but none of the retailers listed it as such - only the manufacturer did. Using that gas block with a hand guard cap would close off half the gas port.
(I see now that zukiphile mentioned the same thing in fewer words.)

 

[tangolima]

The handguard cap of course. I can see it would push the gas forward. Then the dimples will be off. How did you fix the problem? I probably will enlarge the hole in the cap so that it goes over the shoulder. The handguard would be tight, which will require shaving plastic off the handguard lips.

All the gas blocks I have monkeyed with have drill hole of 9/64" (minor diameter of #10-24 screw). The gas port in the barrel is 0.09" for AR 15 rifle. That leaves 0.025" margin around the gas port hole for misalignment. If the handguard cap is thicker than that, it will cut the pie.

Another way to fix is to grind the gas block hole oval to make it...more inclusive.

-TL

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[FrankenMauser]

For that one, I went to a different gas block. I think I ended up with a Troy.

The "dissipator" gas block is now on something else that did not require a handguard cap. (I'm not sure which upper. I've done a lot of parts swapping and "remodeling" lately.)

 

[zukiphile]

Shocking result: I tried a YHM suppressor gasblock on a Ballistic Advantage midlength 13.7. It would not kick out the brass even with a lightweight BCG and empty buffer.

The gas port on the block doesn't look that small. I also have a 13.7 carbine gas barrel with a gas port smaller than the port on this gas block. I'll try it there and see what happens.