Gas block interference 0.002, too much?

[yosemite_sam]

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.

 

[padom]

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.

 

[yosemite_sam]

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.

 

[TonyAngel]

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.

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.

 

[6.5SH]

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.

 

[yosemite_sam]

This is what I got on Amazon and it worked great before. That being said, what is the ideal interference between the components?

Exactly the same? 1-thousandth?

 

[TonyAngel]

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.

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.

 

[6.5SH]

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.

 

[yosemite_sam]

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.

 

[papershredder]

.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.

 

[MontanaMan]

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.

Get a clamp on gas block....................it's the easy button.

MM

 

[yosemite_sam]

Get a clamp on gas block....................it's the easy button.

MM

Any recs for one that will fit under an aero atlas r-one rail?

 

[yosemite_sam]

.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.

So you would not advocate for any thermal fitting?

 

[papershredder]

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.

 

[mattc51]

WOA says they lathe them oversized so you can sand them down for a tighter fit. Get some 600 grit and give it a few twists.

 

[yosemite_sam]

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.

 

[WeR0206]

Any recs for one that will fit under an aero atlas r-one rail?

The daniel defense clamp on block is pretty low profile. I just able to get it to fit under a SOLGW M89 rail

Daniel Defense .750 Clamp On ($58)

Or you could get a shorter rail that ends where the gas block sits

 

[TonyAngel]

Any recs for one that will fit under an aero atlas r-one rail?

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.

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

 

[WeR0206]

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.

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

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

• Daniel Defense .750 Clamp On ($58)
• YHM Clamp on 4140 Gas Block ($18)

 

[fedupflyer]

Get a clamp on gas block....................it's the easy button.

MM

Most of those clamp on will not fit properly under a slim line handguard and will contact the hanguard during firing.

 

[MontanaMan]

Most of those clamp on will not fit properly under a slim line handguard and will contact the hanguard during firing.

There are plenty that will fit, that is absolutely not a constraint today with rails as small as 1.35 ID's.

MM

 

[MontanaMan]

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

• Daniel Defense .750 Clamp On ($58)
• YHM Clamp on 4140 Gas Block ($18)

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

 

[yosemite_sam]

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?

 

[sirhrmechanic]

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?

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

 

[yosemite_sam]

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

Effin awesome advice. Thanks dude

 

[MontanaMan]

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?

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

 

[yosemite_sam]

I’m a little worried about fitting a clamp on under my aero r-one rail as its ID is 1.3 inches.

 

[yosemite_sam]

For those interested, according to this dude who’s seen the schematic it should NEVER be an interference fit or even a line to line fit for that matter.

 

[MontanaMan]

I’m a little worried about fitting a clamp on under my aero r-one rail as its ID is 1.3 inches.

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

 

[yosemite_sam]

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

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.

 

[padom]

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.

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.

 

[TonyAngel]

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?

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.