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Gas Block Won't Fit Barrel

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I recently took part in the Diamond Head group buy. I ordered the VRS™ T 15.0" Free-Floating Handguard along with a low profile gas block to go along with my BCM 18" SS410™ Barrel found here: BCM 18" SPR SS410 Barrel with Rifle Length Gas


As luck would have it, the gas block doesn’t fit. It hits the second ‘step’ of the barrel, where the gas port is located, then stops dead. I’ve tried wiggling it and rocking it, but it literally won’t budge onto that second step. I’ve even tried lubricating both components to no avail.

In the spirit of full disclosure, I did have the barrel cerakoted, but I wouldn’t think that would add enough to the diameter to prevent the gas block from properly fitting. The stamped writing on the barrel is still clearly visible so it’s not thickly coated.

Should I maybe try a clamp on style gas block such as the YHM-9384, found here: Low Profile Gas Block (Pinch Screw) [YHM-9384] - $33.50 : YHM, Yankee Hill Machine Co., Inc. | Makers of High Quality Firearms, Accessories & Sound Suppressors, Makers of High Quality Firearms, Accessories & Sound Suppressors


Any thoughts, assistance or advice would be greatly appreciated.
 

icyclefar

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You could try putting the barrel in the freezer to cool and shrink it, and heating the gas block in the oven to expand it.

If your only off by a few thousand's it should work.
 
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You could try putting the barrel in the freezer to cool and shrink it, and heating the gas block in the oven to expand it.

If your only off by a few thousand's it should work.

Clever!! I'll give that a shot! Only problem is if it ever needs to come off...
 
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beaker

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The gas block mounting area should not be ceracoated as the clearance is very small. If you have a decent caliper or micrometer measure the diameter if the gas block area to see if is now oversized. You may have to strip off the ceracoat to get a standard gas block on. If it is a split type with screws you may get it on.

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i put a very similar block (your backup one you linked to) on my girlfriend's AR--it has screws but is not the pinch-style. we still had to coat the inside of the block with silicone lubricant to facilitate getting it over the barrel IIRC.
 
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The gas block mounting area should not be ceracoated

Didn't know this! Didn't think it would matter much seeing as how easily they typically seem to go on.

You may have to strip off the ceracoat

I'd rather not...that will suck ass!

If it is a split type with screws you may get it on.

Fingers crossed. I'll strip the cerakote if i have to, but I'd rather not...it looks pissah!


i put a very similar block (your backup one you linked to) on my girlfriend's AR--it has screws but is not the pinch-style. we still had to coat the inside of the block with silicone lubricant to facilitate getting it over the barrel IIRC.

I don't have that block yet, but I just ordered one. Hopefully since it's split, I can get it on. If not, I'll be stripping the cerakote from that section of the barrel.
 
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The gas block mounting area should not be ceracoated as the clearance is very small. If you have a decent caliper or micrometer measure the diameter if the gas block area to see if is now oversized. You may have to strip off the ceracoat to get a standard gas block on. If it is a split type with screws you may get it on.

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This! Cerakote and Duracoat apply at about .002" of an inch thick over the surface - per coat. Meaning on a round part you've added .004" to the diameter of the barrel. That is enough to throw the barrel out of tolerance and keep the gas block from fitting. You're going to have to sand the coating off the barrel in the area of the gas block. In the future install a junker gas block when applying such coatings to cover the area, tape the area off, or paint it with the gas block installed.

To remove the existing coating I would recommend turning the barrel in a lathe at this point and using a fine emery cloth. You want to evenly remove the finish form the barrel at this point - but not any material from the barrel itself.
 
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i think with the split block you'll have much better luck.

Fingers crossed and lesson learned.

If it doesn't work, it's going to be a pain in the buttocks. I don't have a lathe (as Prebanman suggested)...so I'll have to strip it by hand...or scrap it and get another barrel which would be a costly mistake.

- - - Updated - - -

This! Cerakote and Duracoat apply at about .002" of an inch thick over the surface - per coat. Meaning on a round part you've added .004" to the diameter of the barrel. That is enough to throw the barrel out of tolerance and keep the gas block from fitting. You're going to have to sand the coating off the barrel in the area of the gas block. In the future install a junker gas block when applying such coatings to cover the area, tape the area off, or paint it with the gas block installed.

Yeah, it was a dumb idea, I see that now. I should have taped that whole section...or skipped the process in the first place. It looks really nice though...might be the nicest bit of useful scrap I own.
 

01SVTvert

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Take a piece of wet dry 600 sandpaper, cut a long strip and curve it around the barrel at the gas block. Use water and polish it until the coating is gone. Easy enough as long as you rotate the barrel and sandpaper as you go.
 
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Take a piece of wet dry 600 sandpaper, cut a long strip and curve it around the barrel at the gas block. Use water and polish it until the coating is gone. Easy enough as long as you rotate the barrel and sandpaper as you go.

If it comes to this, it's what I'll do. Thanks! I have about a 3" length that will have to be stripped. Dammit, I hate when I go FR.
 
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Don't mess with the barrel. Lighty sand the inside of the gasblock untill it slides on. Better to mess with the finish on the ID of an inexpensive gasblock than ruin a ceracoat job and mess with your barrel.

I know, I'm new here; hopefully that doesn't discredit me.
 

KMS

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Always take material off the inside of the gas block not the barrel,I know it's an AR every AK build I do Romanian Hungarian Saiga ect ect,I have done all the methods.I use a press and gig but still sand a bit.

Sand the inside of the GB with 220 and a wooden dowel the right size.

NSwish is correct.
 
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I would be inclined to agree with removing material from the gas block were we not removing just a finish from the barrel. But paint will remove easier then steel, so I would go after the barrel. Cerakote is just a tough finish, but it's not nearly as difficult to precisely remove as as steel.
 
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I had to polish that part of the barrel with some 600 to get the stock coating of my Spikes barrel to mate up with the Diamondhead block. Had to do the inside of the block as well.

I think cerakote would have a similar applied thickness, more if applied over the stock finish.

If I get my barrel cerakoted, I will leave the block in place I think.
 
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If I get my barrel cerakoted, I will leave the block in place I think.

I didn't think to put it on ahead of time. If I were to do it again, I'd definitely install the gas block first.

First thing I'm going to try is one of those split gas blocks. At least that will give me a little play. If that doesn't work, then I'll try sanding the inside of the block, and lastly sanding the cerakote off the barrel.

My last resort is to scrap the barrel and just buy a new one, but given the price and availability of barrels nowadays, I'd like to avoid that option if at all possible.
 

beaker

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I would just get some 600 grit emory cloth strips, tape off the areas you don't want to strip above and below the gas block diameter. Cut the emory to the right width (same as the block). Wrap the emory around the area you want to strip, maybe about 3 layers thick and spin it with your hand. It will come off, then do the same thing with some 800 emory to clean it up. Shouldn't take too long and you should be able to save the ceracoat finish if you are careful.

Also, if you know anyone with a blast cabinet, you could easily remove it with 120 grit aluminum oxide. Tape off (a few layers) the areas you don't want to clean, and clean up the diameter where the ceracoat needs to be removed. If done carefully, it would also work pretty well.
 
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01SVTvert

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Trying to sand the inside of a circle equally (gas block) is a lot harder than using a strip and carefully burnishing off a couple thou worth of ceracoat on a barrel. If you take your time and go slow so the bore of the gas block doesn't distort that works, but many would try and rush this and end up with an oblong gas block bore.
Tape off everywhere but where the gas block fits on the barrel and it wouldn't be noticeable.

Heat the block up in boilng water and freeze the barrel when you go to fit them if you are still slightly too tight.
 

KMM696

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They only way I'd try enlarging the gas block is if I could find a brake cylinder hone that would work down to 3/4". Maybe motorcycle tool companies?

Otherwise, see 'sand off Cerakote' above. The tolerances between the gas cylinder and barrel are tight for a reason, and I'd hate to muck that up.
 
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They only way I'd try enlarging the gas block is if I could find a brake cylinder hone that would work down to 3/4". Maybe motorcycle tool companies?

Otherwise, see 'sand off Cerakote' above. The tolerances between the gas cylinder and barrel are tight for a reason, and I'd hate to muck that up.

I was going to suggest this (using a hone) but removing the finish from the barrel is just the only way to go in my mind. But if you had to attack the gas block you need to use a tool such as a hone to insure material is removed evenly and the hole does not go out of round. There is absolutely no way that can be done by hand. A hone and a drill press would be the minimum tools required for such a job. Even a hand drill can remove material unevenly and the hole will will no longer be square with the block. You may not knock it off by much, but you'll knock it off.

Removing the finish on the barrel is the only safe method here - without access to a machine shop and/or necessary tools. Beaker had good advice if you do not have access to a machine to turn the barrel.
 

KMM696

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Removing the finish on the barrel is the only safe method here - without access to a machine shop and/or necessary tools. Beaker had good advice if you do not have access to a machine to turn the barrel.


Yep - although I'm not sure taping off is going to help preserve the finish. The block will have to slide over the whole step of the barrel that's gas port diameter, and since the OP suggests that it stuck immediately, I'm thinking the finish will probably have to come off that whole section. Hopefully, Cerakote doesn't have much color variation from lot to lot.
 

beaker

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I think it will come off the area of the barrel pretty easily with Emory. Just cut it in a strip the same width as the gas block and use the gas block step as a stop. Wrap it around that area, put on Chubby Checker and twist away. I give it 10 minutes tops.

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beaker

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Awesome! Glad it worked out well!

Okay, so I bought one of these: Low Profile Gas Block (Pinch Screw) [YHM-9384] - $33.50 : YHM, Yankee Hill Machine Co., Inc. | Makers of High Quality Firearms, Accessories & Sound Suppressors, Makers of High Quality Firearms, Accessories & Sound Suppressors

And it fit fine. It was perfect, I didn't have to muscle it on or anything. It's a bit of a relief, as I was not looking forward to sanding the cerakote from about 4" of the barrel.
 
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