Quick Tip: AR-15 Gas Block Alignment
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- Опубліковано 9 лют 2025
- Brownells Gun Tech™ Caleb Savant is here to set the record straight once and for all about AR-15 gas block alignment. Getting the gas block correctly aligned IS important, but it's not as difficult or fiddly as you might think it is. Some folks insist that when you're installing a gas block on a free-floating barrel, you should not push it tight against the barrel's gas block shoulder. They say you should leave a small gap between the gas block and the shoulder so there's room for the ring on a two-piece snap-on M4- or A2-type handguard. You should do this even when you're not using that type of handguard because the gas block is actually DESIGNED to require the gap. If you don't provide the gap, they say, the gas hole in the block won't line up with the gas port in the barrel.
This is actually NOT TRUE for gas blocks on 5.56 / .223 AR-15s. The gas hole in the gas block is larger than the barrel's gas port, so you don't have to be OCD precise about lining up the holes. Caleb uses his handy borescope to show us what's going on inside the barrel when he pushes the gas block right up against the shoulder of the barrel. Yep, the holes line up with no obstruction of the gas flow.
If the barrel you're working with has a dimple for a gas block setscrew, go ahead and align the block based on the dimple. But if the barrel is not dimpled OR if you're using a clamp-on gas block, it's totally OK to run the gas block all the way up against the shoulder. The gas will still flow, and your AR will cycle. NOTE: This rule applies consistently only to AR-15s chambered in 5.56 NATO / .223 Remington.
Gas block alignment can make or break a build, but there is more room for error than you think!
So, how do I find, for example, the bore scope Caleb used at Brownells? I tried “digital bore scope” and other permutations in Search at the new and improved web site and only got a little Lyman scope and one other. Harbor Freight, maybe?
@@CaveWyatt Ask your local proctologist.
@@CaveWyatt Search "Teslong" or "borescope" on Brownells
@@mostlypeacefulmisterputin Aircraft engine mechanics, industrial and electric generation gas turbine mechanics as well.
Crazy bc I was just looking for videos like this
I just use a piece of dry spaghetti to align the holes. When it is all done, break and remove the spaghetti with cleaning rod.
I recently bought my first AR-15 and had no idea how they work internally, but after watching your videos and a few other UA-cam videos I think I understand what's happening inside. Thank you for explaining things in a way even I can understand.
Good on you for taking the time to learn about it. Not everyone does. You’ll be a better shooter and safer if you know how the gun works.
It’s a very simple firearm which is why I love it. The only firearms I know of that’s simpler are Glocks, and I love them too. Hell I have 7 “ghost gun” Glocks, not to mention two AR15s and an LR-308 “ghost guns” as well. TOO EASY and many more to come 😊
While the AK’s functionality is simpler than an AR, building one from parts kits is a lot harder than ARs unless you know what you’re doing and have the right tools, and the tools can get expensive along with the parts kits, depending on what parts kit you get.
Welcome to the Stoner family!
I’ve done a lot of uppers with the set screw bottom and the easiest way to tell where you need to position the gas block is just hold the set screw hole along side the barrels gashole to see if you need the space or not. It’s quick and you can do it by sliding the block on the barrel and flipping the gas block upside down to center the hole because the set screw should be right in line with the gas port in the block or hold it along side the barrel. Assuming everything else was made right it should line up nice and easy. (Obviously this wouldn’t work with the particular gas block in the video but I think the clamp on style isn’t used as much)
Roll the gas block over 180 degrees, center the gas port in the screw hole of the gas block, and use feeler gauges to determine how far off the shoulder you should be.
My theory is that if you get the fore/aft alignment optimized, there’s more room for error in the right/left alignment.
Thank you for clearing up the myth that you MUST leave space between the gas block and shoulder. So many people just repeat something they heard someone else say but dont actually know the information for themselves.
Depends on the gas block design, some are designed to fill the gap.
I personally never put different metal alloys butted against one another when he becomes involved. I like to give thermal expansion a little room. Other than that I cannot think of an issue.
Don’t be a gashole!!!Myth confirmed.
1:41 to hear it again
I was soooo stressed out about gas block alignment when I built my first ar. I must have done it right though, because It shoots perfectly. (And I did push it all the the way against the shoulder)
Lol yes I stressed the hell out of this myself, until I finally got a thorough observation of the gas block and noticed the porthole size was about three times bigger. I think what a lot of us do, is watch videos of people overthinking this process. I know I did!
In the end, the holes gotta line up. If you did that you are good
Good timing.
I'm swapping barrels and gas blocks this week.
I always click on uze gyz when you pop up.
Your info is always of value........
I'm just here for the "reeee!" responses.
A picture is worth a thousand words ! Thanks for clarifying positioning of a 223 gas block.
Either way is correct. I like the Kaw Valley jig and recommend it highly if you're using a gas block with set screws on the bottom. It allows you to easily perfectly center the gas block hole over the gas port in the barrel. I know that it being perfectly centered is not "necessary" but that's what I prefer.
Doing God's work Caleb, whether it's your first build or tenth can always learn something new!
That is genuinely helpful information. Thank you.
It would be interesting to take 3 or 4 barrels and 3 or 4 common gas blocks and see if that standard applies across the board.
It applies for many, but not all. Ask me how I know lol.
SOLGW FCD for instance come with knurled set screws in the bottom, dimpling pre-drilled into the barrel to line up properly. They also make a jig you can buy, or 3d print, for dimpling any barrel.
@@xSP3CTREx Pretty common features of any mid tier upper and above, even low tier.
With that said, those features don't change the question of whether there is enough variance in barrel and gas block manufacturing that putting the gas block tight against the shoulder versus 0.025" out would misalign the gas port/gas block. Which the first poster seems to confirm does happen.
@@JimYeats You've answered your own question. If these are common enough features across the board then there shouldn't be any deviation unless you buy literal blocks meant for airsoft replicas which wouldn't even need ports. Notice how they don't say what block barrel combo 'trust me bro'. My theory is the mounting hardware matters more, if the block isn't pinned to the barrel it can rotate without knurled screws into a dimple counteract. The type Caleb has in the video would shift real easy if not torqued and high temp threadlocker.
@@xSP3CTREx Oh hey you're right, everyone makes perfect products with no errors, deviations, tolerance stacking, or poor QC! No bad/different products out there at all! With the literal hundreds upon hundreds of barrel and gas block makers out there, no chance of issue at all.
It's anticipated that you are responsible for lining up your gas block. Personally I both measure and use the first set screw hole to confirm. The point of the comment is for people who are just blindly assuming what the depth of the gas block should be and not actually checking themselves and only ensuring the vertical alignment is correct.
This video came at just the right time for me! I have a new .300 Blackout upper that wasn't ejecting the spent casing, so I took the handguard off and found that the gas block hadn't been locked down. I was wondering how far back I needed to set it, and your video answered my question. Thanks! 😊
I had one block that when tight against the shoulder the BCG would not go all the way forward without a lot of resistance. It positioned the gas tube too far back and it was bottoming out in the carrier key. Left a gap between the block and shoulder and it solved the problem. Probably a tolerance stacking issue but it can matter.
This is the reason why it does matter...
Your videos are always so straightforward and helpful. Thank you.
Thank you for sharing the secrets of the gashole
Back when I started my addiction, I read somewhere that unless I was using the 2 piece hand guard, that I just butt the gas block to the shoulder. Lately, I read that I was supposed to be leaving a gap. But they all shoot fine. Thank you for clearing that up.
Some gas blocks are longer than others which will put the gashole closer or farther away from the gas port in the barrel some are made to go against the shoulder and some are made for the handguard plate to go between them an the shoulder have seen when the wrong one was used it wouldn't let inproper alignment of the gas port hole
With the exception of Yankee Hill clamp ons that have the flip up front sight. It's really a good idea to get it aligned proper. And I tell you I have a barrel from another sporting goods store that if you slide the gas block back on it it does block the barrels gas hole enough to cause cycling issues. This brand suffered this alot in their earlier offerings. Reading the comments and ratings page shows that as there were a lot of people drilling them out lager on the barrels. I was and still am using a low profile block on that particular barrel. If I didn't space it I would have had to in large the gas hole on the barrels. Barrel shoots well..
That's why I get dimpled barrels! Don't gotta worry about all that
Excellent video and information. I use a borescope for the same reason and for barrel inspections and for quality control reasons. Thanks.
Is the borescope just the rod that inserts into the barrel and plugs/connects to your phone or is a borescope an entire unit. What type of borescope do you use and what type is being used in this video?
Brownells does it again, thank u bro, very helpful feasible and direct. I have been doing alot more builds lately and revamping some older guns and it dawned on me to check into this before i start breaking them all down to check for dead on alignment. Whew...thank u sir
Great "Show Me" demo - good job, young man!
That is the cleanest gas hole that I have ever seen; they usually have some kind of crap on them.
First off, let me say it may have been my combination however, when I installed an Aero gas block on my AR the gun would barely run so I started investigating the cause. When I pulled the block back off the gun, the carbon ring around the gas hole in the barrel told the story. Butted against the stop on the barrel only about half the gas hole was exposed. After I repositioned the gas block down the barrel about the width of the ring everything worked fine.
Thanks for the video!
I always did this blind with a coat hanger and a slight 90 at the end. Bore scope is way to go though.
A trick a friend of mine showed me is put a spegitti noodle in the gas hole, knock the noodles flush with the top of the barrel. Install gas block, flip the barrel and let the noodle stop the gas block in place. Set your set screws and flip the barrel upright and knock the noodle out.
Hey Caleb, Here's a quick tip for you. Get another shirt. Or make up a Smyth Busters video on the myth "powdered laundry detergents destroy Brownells flannels faster than liquid detergents."
Will you be less salty if we send you one next year BEFORE we sell out?
My mind wasn't in the gutter until Caleb told me to get it out of the gutter.
Hey, my mind wasn’t in the gutter until you brought It up.
Thanks that explains the difference of opinion I had seen in doing my research.
This may apply to a .223 or 5.56x45 barrel, but you'd best ensure precisely correct alignment for the much larger gas max diameter port on a properly made .300 AAC Blackout barrel which is made to deliver max gas to the impingement system.
This is my problem I’m shooting 300blk but it doesn’t eject the casing and shell gets jammed
Up against the shoulder or not depends LARGELY on the gas block itself. The YHM-9383 goes all the way to the shoulder. You verify with the set screw-gas hole technique.
I have used several of the Strike Industries indexable gas blocks on AR15's and LR-308's... perfect alignment every time as you visually line the ports up, due to how the are made and install.
Good to know. I used to stress over that but now, I use dimpling jigs on my barrels for a perfect alignment.
this video was super helpful thank you caleb.
I was taught the the port (gashole😄) on the GB is usually 30% larger (50% in some cases and applications but not usually) than the port on the barrel...thus giving it leeway on alignment...unless it's a sight style GB.
Awesome tip. I’ve always wondered how important that is
I just bought the jig to dimple my barrels that didn’t come with one, no further hassle.
I have a little tool that dimples the barrel while lined up with the gas port. Works without a hitch. No fuss no muss !
Kind of another myth buster. Good one. Thank you.
Itd be super if industry standard was a notch in the shoulder that alinged with a peg in the block or vice versa.
BTW that chrome lined barrel looks nice on the inside!!!!
I love that seems to be an AT-4 in the gunsafe.
I use a piece of dry spaghetti noodle as a gas block alignment tool. I break off the spaghetti in in the gas port and the put the gas block on and turn the barrel upside down. The spaghetti falls into the gas block and locks the gas port hole with the gas block hole. Tighten everything down and turn the barrel right side up and use a cleaning rod to break the spaghetti and push it out of the barrel.
I wish Brownells would align their A1/A2 front sight posts better. The last few I installed had the rifle’s front sight to be canted quite a bit.
You don't say? Hmmmm
Videos like this don't inspire great confidence.
You need to check with your barrel manufacturer and they will help you out. I know Ballistic Advantage has gone away from the gap for the handguard and an SOLGW tells you to push it to the shoulder! I love using a bore scope for checking alignment.
....I used pencil marks on the barrel and gas block to align them and used a length of fish tank air hose attached to the gas tube to blow air intoit to ensure I had the hold aligned properly...BTW I noticed that the hole in the block was larger than the gas port in the barrel...
I can see what Caleb is saying, for a clamp on style. But, you can get a gas block dimple jig from SLR Rifleworks that aligns the gas port on the barrel to the propper placement of the dimple underneath. Set it up and see if its a true alignment. If the barrel doesnt have a dimple already use a drill and bam! Dimple achieved! Just my 2 cents
I had always thought/assumed that, but it’s good to know for a fact!
I had an upper that wouldn't run, pulled the GB, there was an off center burn mark in the inside of the GB. Shifted it forward 2mm, upper started working.
"I'm saying GAS HOLE. Get your minds out the gutter."
*my mind diving deeper into the gutter because it's still a gas hole*
When I have a problem with my gashole, I blame the dog. Love my borescope too.
I've encountered more than one gas block that you could not but it against the shoulder of the barrel always inspect the alignment of the whole never use one specific rule
Superlative arms adjustable gas blocks "gas hole" is a lot smaller than most "gas holes". Now I don't have a bore scope, but I do believe the gap matters on that brand
Specifically the clamp on style from superlative arms
True with mil spec front site post, not aftermarket blocks.
Always great content!
GOLD Caleb, pure GOLD
And even further than that if the gas block is tight on the shoulder it makes everything more ridged and is better for harmonics, if you don't know about harmonics look into them because they are everything
My set screw ones always left that gap if I used the dimple. But I recently got an SI clamp-on toolless adjustable gas block and to install that you align the ports on that gas block to the barrel's port first, which left that gap also. I just leave the gaps. Someone should make a shim to fill that gap so crud doesn't get in there if its a known dimension. I'd buy that.
Great video and well executed stray to the point.
I had tacos last night and my gas hole is feelin slightly misaligned
I never thought of the spacing .
Do a video of how to make sure these things don't move ....
Thanks. Reassuring.
Excellent video, thanks!
Awesome videos
I am not so sure that this is accurate advice for many gas blocks. A 0.030" barrel shim places the gas block in the correct location, and they come in the different barrel ODs. I also use a borescope for alignment checking on custom builds. I also engineered the robotic assemblers for the barrel index pin and gas block installation on AR barrels.
I do appreciate the advice to check the alignment with the borescooe. The shim may or may nit be needed.
keep about a quarter gap between the journal of the barrel and rear of the gas block, use canned air with a straw on the gas tube from inside the receiver and verify you feel the air out of the muzzle... done...
Not true, you can have over half the gas port covered and still get air through..Better ways to test but the bore scope is still the best way to verify..
@@hairydogstail sure; but why make it more susceptable to failure by having the least amount of port coverage as possible? The more of the port that is covered the more likely you are to have failure with lighter loads. If you are building a dedicated suppressor platform, maybe covering a portion of the port makes more sense if it's not a pass through design can, since there will be more back pressure help with cycling; but otherwise it's just less reliable... also regarding the bore scope, I agree... im simply talking about a way that most people can at least verify they have flow, being that people rarely have bore scopes...
@@boss350z5 I think we got lost in transition. I agree the port should not be covered. What I was trying to say is if gas blows through the port like you suggested, the port could still be blocked by half..Best way to verify port alignment is with a bore scope or remove after use and verify carbon ring around gas port..
@@hairydogstail Ah... gotcha, so were saying the same thing, you're just pointing out that using canned air isnt the optimal method of testing, I'm simply listing it as a quick and dirty method that is fairly effective, though not as effective, admittedly, as a bore scope or checking for carbon ring deposit after test firing... fair. Simple misunderstanding.
They should put a little divot in the top of the barrel and GB manufacturers should leave a small piece that inserts into the divot. Would make things much simpler. I've never had an issue with it for the most part but installing an FSB...well...getting that alignment just right without repeated eyeballing would be nice.
Very cool video! Thanks!
Gas hole. Cracked me up.
Outstanding! Thank you 👍🏻😊
Thanks for this information!!! Great video.
Outstanding!
So, the moral of the story is when you're dealing with a gashole,just remember: It's a bigger gashole than you think!
Thank you 😊
Awesome, thank you!!!
While it may still work pushed all the way back it's not optimal, correct, or Mil-Spec to be. There's supposed to be a 0.025" gap in order to fit the hand-guard cap. You don't sell them but there are 0.025" spacer washers available elsewhere in 0.625" and 0.750" diameter as well as some others. This is specifically for clamp on gas blocks and removable fold down clamp on FSBs like the Yankee Hill Machine....love that one in particular (YHM-9394). On set screw style blocks your gas port and dimpling jig will align the gas block correctly being off the shoulder. I don't bother with the spacer washer with them. On any of the variety of clamp on gas blocks or clamp on FSBs you really should use them. That way your forward and rearward movement is irrelevant and all you need to worry about is side to side. It also gives extra piece of mind that with careless or rough handling the gas block won't be going anywhere causing misalignment issues.
I've noticed this myself with my cheapo bore scope. I use dimple jigs and rocksett on all my gas blocks. An I always check alignment before I add the Rocksett. An the room for error is not insignificant.
thanks
Excellent
All my life Ive been pursuing gasholes.
Did not know that about the alignment on the shoulder. Thought you had to offset it.
Crap. Now I want a bore scope.
"Gas hole." Maybe that's what my wife's been calling me for years, and all this time I thought she was calling me something else! How 'bout that!
Thank you for the video.
“The more you know.” 🎉
When all else fails, I just use a piece of dry spaghetti. So much cheaper than a borescope but they are a nice tool to have.
and I thought that was my secret / Mac Gyver to do.......BUZZ
@@johnd843I can’t figure out how on earth you would use a piece of spaghetti ???
@@robertlipsey6056 Break off a piece in the barrel where it's in the bottom of the bore. Then you can add your gas block and turn 180 degrees and let it fall into the gas block. Drop a cleaning rod down the bore to break the noodle. Then you know they are in alignment. A country boy way of doing things & not a NASA lab tech doing the work...IMO
@@johnd843 Thanks for the comment. I would have never thought of something like that. I can see how it would work though. It might be easier to just buy dimpled barrels. lol
That's so funny, that's what I call one of my bosses
A Gas-Hole
Good info. Now I need a bore scope, haha.
We have several gasholes that are misaligned in the whitehouse
I installed a gas block recently and the directions from the manufacturer actually said to leave a gap (can't remember the exact distance). It was for an AR-10 so maybe it makes a difference. I'll have to pull out my borescope and check.
.025 inches.
@@ShortArmOfGod thanks. I knew it was .02 something but couldn't remember.
I chuckled a bit when he said "gas hole" the first time
A dumpling jig isn’t complicated to figure out. Though first time drilling into a $500 barrel you choc starfish will pucker something fierce.
Thx
Bottom line, measure it. I've seen tapered and flat edges on both the barrel and the gas block. It might be flush, it might be floating over the two tapered edges, it could be set back like if there were a handguard plate between the parts.
Gasshole lmao
I did not know that 😳. Thanks
Or you just buy a Monobloc barrel from HM Defense where the gas block is actually CNC machined as an integral part of the barrel itself, eliminating the need for proper gas block alignment or having to hassle with set screws, dimpling, or pinning altogether. 😉
That's interesting. Didn't even know that was an offering. I could see why some people who might want to install an adjustable gas system to pair with specific suppressors wouldn't want that. But for other people that would be a solid solution and you still could run a low backpressure suppressor I suppose. Options are good.