Gas block interference 0.002, too much?

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yosemite_sam

Sergeant of the Hide
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Jan 21, 2023
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#1
My WOA SPR gas block journal OD is measuring 0.752 and my Geiselle super gas block ID is 0.750. So looking at 0.002 interference.

According to ChatGPT, if I heat the gas block to 450 degrees, and the barrel is in the freezer overnight, it should gain me 0.0021 clearance for a thermal fit.

Yes I understand that I can hone the gas block and polish the journal.

Anyways, am I crazy to be concerned about the gas block constricting the bore once everything comes back to room temperature? Main concern for constricting is the bore would be affecting accuracy and durability.

I know that a lot of folks have done thermal fits with their WOA barrels but wanted to know what level of interference starts being too much. I presume there is a safe limit.

Flame away.
 
#2
Nope your concern is warranted.. I have found my WOA gas journal fit to my Geissele Super gas blocks just too tight. To the point I stopped using the Geissele super gas blocks on them and used Superlative Arms or BCM, etc.
 
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#4
yosemite_sam said:
I’m not opposed to honing the gas block.

I want to know if 0.002 interference is enough to effect accuracy/durability.

Sometimes I wish I was a mechanical engineer.
Click to expand...
If I had to make a guess, I'd say that, at the least, there is a chance of it. I will tell you that getting that gas block off is going to be a chore, if you need to.

Just based on what I've seen an overly tightened muzzle device do to the size of the exit hole on a barrel, I'd say there's a pretty good chance of it.

Just hone it out or get a gas block with a larger internal diameter.
 
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#5
Go to an auto parts store and get an adjustable brake cylinder hone for about $15. If it isn't cutting fast enough you can use strips of wet and dry sand paper and the hone allows it to apply even pressure.

ETA:
This is literally what Brownell's sold for use as a honing tool for shotgun barrel use. It works fine inside of a gas block and I did the same with a BCM block on a WOA 18" SPR barrel.
 
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#6
This is what I got on Amazon and it worked great before. That being said, what is the ideal interference between the components?
IMG_1628.jpeg

Exactly the same? 1-thousandth?
 
#7
6.5SH said:
Go to an auto parts store and get an adjustable brake cylinder hone for about $15. If it isn't cutting fast enough you can use strips of wet and dry sand paper and the hone allows it to apply even pressure.

ETA:
This is literally what Brownell's sold for use as a honing tool for shotgun barrel use. It works fine inside of a gas block and I did the same with a BCM block on a WOA 18" SPR barrel.
Click to expand...
Thank you for mentioning that. I posted about using a similar tool in another thread and, for the life of me, couldn't remember what I bought it for. It was driving me nuts.
 
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#8
Go slow, flush it with brake parts cleaner and periodically check the fit. I'd not go so tight that it needs more than firm hand pressure to seat it.
You also don't want it so loose that it leaks.
 
#9
I’m aware of how to hone a GB I’ve done it several times.

I want to steer the discussion back towards what do we think is the ideal difference in size between GB and journal is. Is thermal fitting a good practice or should parts fit at room temp with hand pressure.

Also if folks wanna post their stories of what they fitted and what the ID/OD of their parts measured out to.
 
#10
.002" is getting into press fit territory. If the wall thickness of the block is thin enough, it could break. Ideal would be ID of block about .0002-.0005" larger than OD of journal. In that range, thermal expansion during firing would seal it off, and once it cools, can be removed easily if needed. Also, set screw and clamp style blocks naturally seal up the port just by the way the tension is applied to hold the block in place. Assuming the surface finish of both ID and OD are adequately smooth which is something to keep in mind if you try honing to fit.
 
#11
yosemite_sam said:
My WOA SPR gas block journal OD is measuring 0.752 and my Geiselle super gas block ID is 0.750. So looking at 0.002 interference.

According to ChatGPT, if I heat the gas block to 450 degrees, and the barrel is in the freezer overnight, it should gain me 0.0021 clearance for a thermal fit.

Yes I understand that I can hone the gas block and polish the journal.

Anyways, am I crazy to be concerned about the gas block constricting the bore once everything comes back to room temperature? Main concern for constricting is the bore would be affecting accuracy and durability.

I know that a lot of folks have done thermal fits with their WOA barrels but wanted to know what level of interference starts being too much. I presume there is a safe limit.

Flame away.
Click to expand...
Get a clamp on gas block....................it's the easy button.

MM
 
#13
papershredder said:
.002" is getting into press fit territory. If the wall thickness of the block is thin enough, it could break. Ideal would be ID of block about .0002-.0005" larger than OD of journal. In that range, thermal expansion during firing would seal it off, and once it cools, can be removed easily if needed. Also, set screw and clamp style blocks naturally seal up the port just by the way the tension is applied to hold the block in place. Assuming the surface finish of both ID and OD are adequately smooth which is something to keep in mind if you try honing to fit.
Click to expand...
So you would not advocate for any thermal fitting?
 
#14
By press fitting I meant needing an arbor or hydraulic press, but no, thermal fitting of a gas block is overkill, IMO. Just as long as the fit isn't too sloppy loose, like more than a thousandth or two, eventually what's going to happen over time is carbon fouling will seal up the gap between gas block and journal. More than a .002" slip fit, I would find another gas block.
 
#16
I know WOA says to polish the journal but I never liked that logic. How am I supposed to get 0.002 off the journal by hand and still make sure it’s concentric(without a lathe).

IMO I have a much better chance of honing the inside of the gb to maintain concentricity.

 
#18
yosemite_sam said:
Any recs for one that will fit under an aero atlas r-one rail?
Click to expand...
The problem with clamp on gas blocks is that they are typically more chunky. I have a yankee hill clamp on that has a hinge on it. Its probably the least chunky clamp on I've seen.

yhm.net

Hinged Low Profile Gas Block (.750") - YHM-9345

This hinged low-profile gas block is .750 ID, allowing you to install it to a barrel with a pinned and welded muzzle device. Shop now!
yhm.net yhm.net
 
#19
TonyAngel said:
The problem with clamp on gas blocks is that they are typically more chunky. I have a yankee hill clamp on that has a hinge on it. Its probably the least chunky clamp on I've seen.

yhm.net

Hinged Low Profile Gas Block (.750") - YHM-9345

This hinged low-profile gas block is .750 ID, allowing you to install it to a barrel with a pinned and welded muzzle device. Shop now!
yhm.net yhm.net
Click to expand...
I have an unhinged YHM clamp on and DD clamp on and the DD is a smidge smaller and easier to fit under most handguards. Vltor seems to make a decent clamp on but I'm not sure on how bulky they are
 
#22
WeR0206 said:
I have an unhinged YHM clamp on and DD clamp on and the DD is a smidge smaller and easier to fit under most handguards. Vltor seems to make a decent clamp on but I'm not sure on how bulky they are
Click to expand...
Vltor's won't fit most smaller ID handguards...............the design of the screws & their heads will usually interfere.

SLR's, ODIN & Wojtek are your friends..........................but there are plenty of others.

MM
 
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#23
I wanna move the discussion back towards the original post. I appreciate the discussion about clamp blocks though, thanks.

I like to run a coil pinned block on my builds.

What do folks think is an ideal slip/interference between the block and journal? Is thermal fitting a desirable solution.

And yes I think most of us know that carbon fouling will eventually seal the block. But if that’s the standard way then why does WOA want such a tight fit?
 
#24
yosemite_sam said:
This is what I got on Amazon and it worked great before. That being said, what is the ideal interference between the components?
View attachment 8770777
Exactly the same? 1-thousandth?
Click to expand...

Only issue with ball Hones is they tend to hourglass things internally.

Brake hone is better for home shop use as the stones are rigid.

If you have a machine shop in Town with a pin hone, that will be ideal!! Long rigid coolant fed hone. They are very repeatable and a good hone operator can take out a couple of tenths in seconds and get exact to a tenth or better.

Sirhr
 
Last edited:
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#25
sirhrmechanic said:
Only issue with ball Hones is they tend to hourglass things internally.

Brake hone is better for home shop use as the stones are rigid.

If you have a machine shop in Town with a pin hone, that will be ideal!! Long rigid coolant fed hone. They are very repeatable and a good hone operator can take out a couple of tenths in seconds and get exact to a tenth or better.

Sirhr
Click to expand...
Effin awesome advice. Thanks dude:)
 
#26
yosemite_sam said:
I wanna move the discussion back towards the original post. I appreciate the discussion about clamp blocks though, thanks.

I like to run a coil pinned block on my builds.

What do folks think is an ideal slip/interference between the block and journal? Is thermal fitting a desirable solution.

And yes I think most of us know that carbon fouling will eventually seal the block. But if that’s the standard way then why does WOA want such a tight fit?
Click to expand...
There really should not be an "interference" fit. If it's too tight to be able to lightly tap it into place, then it's too tight.

The set screws or a pin, or both, is what is intended to keep it in place.

If I use a WOA barrel, it gets a clamp on block which always gives a tighter fit anyway, by design, if it's a decent GB.

MM
 
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#29
yosemite_sam said:
I’m a little worried about fitting a clamp on under my aero r-one rail as its ID is 1.3 inches.
Click to expand...
Obviously, you've not done many builds...............

Attached is a link to SLR's website & handguards. Scroll to the bottom on the page & look at the Ion series handguards cross section with dimensions.

All the SLR clamp on GB's will fit that handguard which is 1.300" ID.................same as your Aero. Same as BCM, same as Geiselle '14's & 16's.

So it will fit.

So will the Wojtek (link below). They have 2 versions, both will fit..........and both work just fine, tho I prefer the cheaper version.

So will the WMD (link below)

These are all adjustable; if you don't want / need to adjust for different ammo / conditions, find the setting that works for your setup, lock it in, & leave it. Easy, peasy.

There is absolutely zero magic in the Geiselle GB....................it's no better or worse than most others.

SLR

Wojtek

WMD

MM
 
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#30
MontanaMan said:
Obviously, you've not done many builds...............

Attached is a link to SLR's website & handguards. Scroll to the bottom on the page & look at the Ion series handguards cross section with dimensions.

All the SLR clamp on GB's will fit that handguard which is 1.300" ID.................same as your Aero. Same as BCM, same as Geiselle '14's & 16's.

So it will fit.

So will the Wojtek (link below). They have 2 versions, both will fit..........and both work just fine, tho I prefer the cheaper version.

So will the WMD (link below)

These are all adjustable; if you don't want / need to adjust for different ammo / conditions, find the setting that works for your setup, lock it in, & leave it. Easy, peasy.

There is absolutely zero magic in the Geiselle GB....................it's no better or worse than most others.

SLR

Wojtek

WMD

MM
Click to expand...
Screen Shot 2025-09-22 at 10.47.06 AM.png


Read the last part, you're saying this is not the case? The schematic/cross section that SLR has for their .750 gas block does not denote that it is a clamp on or set screw. Unknown if they have the same cross section. $130 is a big investment only to find out it doesn't fit.
 
#31
yosemite_sam said:
View attachment 8772606

Read the last part, you're saying this is not the case? The schematic/cross section that SLR has for their .750 gas block does not denote that it is a clamp on or set screw. Unknown if they have the same cross section. $130 is a big investment only to find out it doesn't fit.
Click to expand...


Im in your same boat, clamp-ons are a no go with all the popular handguards I want to use (Geissele, BCM MCMR,)....

But, the Superlative Arms adjustable set screw went right on my latest WOA Krieger as well as an older Syrac AGB... I am a HUGE user of Geissele super gas blocks but they just dont fit on the last 3 WOA's. They 100% need to be honed/opened up or gas journal honed to use.
 
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#32
yosemite_sam said:
I wanna move the discussion back towards the original post. I appreciate the discussion about clamp blocks though, thanks.

I like to run a coil pinned block on my builds.

What do folks think is an ideal slip/interference between the block and journal? Is thermal fitting a desirable solution.

And yes I think most of us know that carbon fouling will eventually seal the block. But if that’s the standard way then why does WOA want such a tight fit?
Click to expand...
Man, I totally get that you're building something a bit special. You got yourself a nice barrel and you want it to be right. Still, I think you're burning way too many brain cells on this.

I think we've agreed that too tight is bad, so that leaves you with the flip side. I wouldn't worry so much about measuring things and looking for that magic number that will get you the perfect fit. You just don't want to have to use force to get the gas block on.

If you're gonna hone it out to fit, just do so to the point where the gas block slips over the journal. If your wish to go with a clamp on is to have a tight fit, you're wasting your time. It isn't going to get you any sort of benefit and, unless you're running a pinned and welded rig, it can cause fitment problems.

Honestly, I use riflespeed gas blocks these days and they can be on the loose side on some barrels and Ive never had a problem. After a few thousand rounds, the carbon does what it does. Sometimes getting them off means using some sort of carbon cutter and a touch of heat.

I dont know if this will be your first time using that handguard, but I tried the ballistic advantage version with my first riflespeed. Although I was able to get it together with what I thought was a good amount of clearance, it turned out that the handguard had a lot of flex in it and was contacting the gas block when firing. I went with a different handguard. You might want to check that.
 
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#33
TonyAngel said:
Man, I totally get that you're building something a bit special. You got yourself a nice barrel and you want it to be right. Still, I think you're burning way too many brain cells on this.

I think we've agreed that too tight is bad, so that leaves you with the flip side. I wouldn't worry so much about measuring things and looking for that magic number that will get you the perfect fit. You just don't want to have to use force to get the gas block on.

If you're gonna hone it out to fit, just do so to the point where the gas block slips over the journal. If your wish to go with a clamp on is to have a tight fit, you're wasting your time. It isn't going to get you any sort of benefit and, unless you're running a pinned and welded rig, it can cause fitment problems.

Honestly, I use riflespeed gas blocks these days and they can be on the loose side on some barrels and Ive never had a problem. After a few thousand rounds, the carbon does what it does. Sometimes getting them off means using some sort of carbon cutter and a touch of heat.

I dont know if this will be your first time using that handguard, but I tried the ballistic advantage version with my first riflespeed. Although I was able to get it together with what I thought was a good amount of clearance, it turned out that the handguard had a lot of flex in it and was contacting the gas block when firing. I went with a different handguard. You might want to check that.
Click to expand...
This ^^^
 
#34
yosemite_sam said:
View attachment 8772606

Read the last part, you're saying this is not the case? The schematic/cross section that SLR has for their .750 gas block does not denote that it is a clamp on or set screw. Unknown if they have the same cross section. $130 is a big investment only to find out it doesn't fit.
Click to expand...
As I said, the AGB's I mentioned will fit inside Geiselle & BCM & naturally SLR's..................I know that because I've used them there. I have never used an Aero rails in 30 something builds so I cannot guarantee, but both Geiselle & BCM are small.

But the original post about interference on a non-clamp GB is telling.

YMMV

MM
 
#35
I'd never use an interference fit on a gas block... silly idea, more harm than good.
Especially .002" interference fit.

No need for it, no benefit..but makes it harder to disassemble.
Mine are all slip fit...even non standard gas journals, are fitted with a slip fit as shown.

But it's yours... so put a slide hammer pipe on it and pound it on...

It's like my cartridges will shoot better if they have a tight interference fit with the chamber....it's that stupid.
 

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#36
yosemite_sam said:
My WOA SPR gas block journal OD is measuring 0.752 and my Geiselle super gas block ID is 0.750. So looking at 0.002 interference.

According to ChatGPT, if I heat the gas block to 450 degrees, and the barrel is in the freezer overnight, it should gain me 0.0021 clearance for a thermal fit.

Yes I understand that I can hone the gas block and polish the journal.

Anyways, am I crazy to be concerned about the gas block constricting the bore once everything comes back to room temperature? Main concern for constricting is the bore would be affecting accuracy and durability.

I know that a lot of folks have done thermal fits with their WOA barrels but wanted to know what level of interference starts being too much. I presume there is a safe limit.

Flame away.
Click to expand...
I thermally fitted a gas block on a WOA SPR barrel. I first sanded the journal quite a bit, until I could almost tap it on but not quite. I got tired of sanding the journal and heated up the gas block and it slid right on, easily. I actually really like the idea of it. It doesn't leak gas and it makes the set screws almost a notional formality. I've had set screws back out and a gas block start to slide forward. I know a lot of people will say if you properly torque and apply thread locker they will never come loose, but I've seen it. And then there's Ridgeline's take that they theorize that dimpling a barrel for set screws might inhibit accuracy so they went to the expense of making a keyed interface gas block and securing it with a jam nut. So there's all sorts of ideas and theories about the effect of gas block securing on precision barrels, none of them conclusively proven.

As far as my thermally fit gas block barrel. It's the most accurate and consistently accurate AR I own. 6x5 at 100. Those little white squares are about .3" -.5" .

1000008352.png


I recently had a large frame barrel made and asked for a slight interference fit on the journal. It required light tapping with a plastic hammer to seat. Here's how it shoots.

1000007407.jpg


I prefer a slight interference fit. Ideally a gas block doesn't leak and doesn't come loose, right? As long as you have the gun gassed right and accuracy is there...why wouldn't you?
 
#37
Most of my ARs are capable of half inch 5 shot groups or less much of the time.
None has a has an interference fit on the gas block....and never will. As I see No need for it. A nice slip fit does the job as intended.
That's not where the "accuracy" is at...just another gimmick to sell, IMO.

Accuracy begins with barrels, bullets, and bedding.
Plus a bunch of other accuracy enhancements that have limited help, like squaring, centering, gluing, properly torqued barrels, and accessories.

One can shoot an AR with the gas block not even attached, or closed off completely on adjustable types, and work the action by hand and still shoot a good AR very accurately, I've done it many times, with subs in particular where there is not enough gas to work the action.

Over gassed, under gassed it still shoots accurately...the brass may take a beating, or it may not load the next round but accuracy is still there. The jammed cartridge pushing the bullet back or bending the cartridge are an accuracy problem and the shooter changing position to clear the jam are the contribute to inaccuracies. The gas block, not so much, cause the AR can be accurate without its presence. It just won't be an auto loader.


But for those who like it, or it gives you confidence, .... continue on.
It's your rifle, do with it, whatever you want.
 
#38
Such an idiot response. As usual from you.

The argument isn't that an interference fit enhances accuracy. The argument made, that I'm showing oppositional data to, is that it could destroy accuracy.

Since no one said an interference fit is the only way to accuracy, you don't have to say anything at all. Just state your position and let other people show their experience. But as usual...
 
#39
JR1200W3 said:
Such an idiot response. As usual from you.

The argument isn't that an interference fit enhances accuracy. The argument made, that I'm showing oppositional data to, is that it could destroy accuracy.

Since no one said an interference fit is the only way to accuracy, you don't have to say anything at all. Just state your position and let other people show their experience. But as usual...
Click to expand...
If ya "have" to make argument that an interference fit "might Not hurt accuracy"...
You already lost the argument...it's illogical to add a step in AR assembly that might hurt accuracy, although I haven't stated that it would, I do not care to find out...cause I'm not foolish enough to buy into such absurdity.

THERE is No Way for it to help accuracy, so there is no reason to do it...logic.

But if there is even a possibility that something could be harmed by forcing a gas block on a barrel depending on how its done and how much force is required to seat the gas block...it definitely not worth messing with...because it has no added value...but has a possibility of producing negative results, depending on variables...a foolish endevor.

It's just an unnecessary gimmick.

But those of you who are forcing on your gas blocks, and loving it, continue to do so.
It's your gun.
 
#40
The reason to do it is to achieve more security than two shitty little grub screws, without the threat to accuracy of more invasive methods like pinning.

It is amazing to me on this forum that people think they need 100 foot pounds of torque to secure a barrel to a bolt action. But they're totally fine using two little grub screws to secure a gas block.
 
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#44
45-90 said:
I'd never use an interference fit on a gas block... silly idea, more harm than good.
Especially .002" interference fit.

No need for it, no benefit..but makes it harder to disassemble.
Mine are all slip fit...even non standard gas journals, are fitted with a slip fit as shown.

But it's yours... so put a slide hammer pipe on it and pound it on...

It's like my cartridges will shoot better if they have a tight interference fit with the chamber....it's that stupid.
Click to expand...
I don’t really like the idea of interference fit parts. It’s not even a part of the stoner design to need to heat the gas block for installation. I don’t want to use anything bigger than my small roll pin hammer to assemble anything on my AR.

What am I looking at in this jig?
 
#47
There is no reliabity issue with the AR gas block as is if installed properly, that can be attributed to a slight gas leak...which will be plugged up with carbon in no time.

Use an adjustable bleed off gas block, adjusted to the ammunition.... it's a gas leak on purpose. Yet works every time for that particular ammunition...

The average max pressure varies every shot in the chamber to give the same variation for each shot in the gas tube...but more pressure than is needed is used to operate the action each time. A little leak or slight variation in gas pressure will not influence operation. As it's always run a bit over gassed to cover those variations by design.
Nothing further is needed in this design for reliable operation. Just the facts

The shoeshine method is moronic.
A good way to get it out of round, like 36 sided but press on the high spots, leaking more gas than the conventional method.

Clamp on or set screw work just fine. As the clamp screws pull the gap closer together, and tight around the barrel. And set screws force the top of the block radius down on the barrel, reducing any gap.

Need more gas, drill the gas port out to a larger diameter...simple and works.

I've ran a gamer 5.56 AR 15 at 1080 rds per minute in short bursts no malfunctions in a thousand rounds, very hot, very dirty...a good way to waste ammo back in the day.

Interference fit... your just fuckin around with a non existing issue, with respect to reliability.

But you go ahead, do your thing, ...hand sand your gas journal and pound your gas block on. "Stupid is as stupid does."
 
#48
Thanks for the permission, I'll keep thermo fitting gas blocks when the option is available. Just shot one today to season a clean bore. Works great, doesn't inhibit accuracy, and gives peace of mind that the whole contraption isn't relying on two tiny set screws.
1000008599.jpg

And sealing the block against leakage is moot point when your gas tube leaks
1000008596.jpg
 
#49
JR1200W3 said:
Thanks for the permission, I'll keep thermo fitting gas blocks when the option is available. Just shot one today to season a clean bore. Works great, doesn't inhibit accuracy, and gives peace of mind that the whole contraption isn't relying on two tiny set screws.
View attachment 8789765
And sealing the block against leakage is moot point when your gas tube leaks
View attachment 8789766
Click to expand...
How do you like that seekins lower? Was thinking of getting one
 
#50
WeR0206 said:
How do you like that seekins lower? Was thinking of getting one
Click to expand...
It's an SP-10 builders kit. The sole reason I bought it was for the semi-monolithic upper/ handguard. Otherwise I'm pretty dispassionate about it. The right side ambi bolt release is a nice to load without breaking position with firing hand grip. I used to think for years the triangular handguards were fugly as hell but functionally they're really nice to work with. Lot's of room inside for gas blocks and bolt on accessories without having to worry about clearance and a flat bottom without any stupid features back towards the magwell that would interfere with an arca rail or a bag.
 
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